ELECTROCATALYTIC AMMONIA SPLITTING WITH MONO-CATIONIC RUTHENIUM COMPLEXES By Mona Maleka Ashtiani A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of Chemistry – Doctor of Philosophy 2023 ABSTRACT The increasing concentration of greenhouse gases in the atmosphere is an inevitable consequence of an energy infrastructure that relies on the combustion of fossil fuels. Thus, finding solutions that reduce or eliminate emissions of CO2 is desirable. Renewable energy sources such as wind and solar are promising solutions; however, storing the intermittently generated energy and distributing the energy for use on demand remains a challenge. Converting energy to high energy-density liquid fuels is preferable for ease of distribution. Ammonia is an attractive fuel option because it is produced from nitrogen which is the most abundant molecule in the atmosphere. Since the reaction of N2 and H2 to produce ammonia is effectively thermoneutral at ambient temperature and pressure, the thermodynamic penalties for storing H2 in ammonia, transporting, and then regenerating H2 at distribution points are acceptable. This would close a zero-carbon fuel cycle. There are two methods for converting ammonia to N2 and H2. The first one is the thermal cracking of ammonia. However, most catalysts have high activation energies and are only effective if the process is run continuously. The second method is electrolysis of ammonia which includes oxidation of ammonia at the anode and reduction of proton at cathode electrodes. One of the main issues in ammonia electrolysis is a requirement of very high potential (~1 V) compared to the thermodynamically determined one, in order to drive anodic and cathodic half-reactions at typical electrodes. This discrepancy between two potentials is referred to overpotential (η) which is needed to drive a reaction at a specific rate. The overpotential can decrease by employing suitable catalysts. The focus of this study is on homogeneous catalysts that can facilitate the ammonia oxidation half-reaction. In a homogeneous electrocatalytic system, a transition metal complex, which dissolves in ammonia solution, is oxidized to a higher oxidation state intermediate by applying potential on an anode. Then, the intermediate oxidizes NH3 in the bulk solution (at the redox potential (E1/2) of the metal complex) and undergoes reduction to the original oxidation. If the E1/2 of the metal complex is lower than the onset potential of ammonia, it can catalyze the oxidation reaction by lowering the overpotential of ammonia. Thus, by designing catalysts with low E1/2, we can decrease the overpotential of ammonia oxidation toward its thermodynamic limit which is 0.1 V vs NHE. In this regard, several well-defined homogeneous catalytic systems for ammonia oxidation have been reported. For example, Habibzadeh et al showed [Ru(trpy)(dmabpy)(NH3)][PF6]2 (1b), which contains a single NH3 ligand, along with tridentate terpyridine (trpy) ligand and bidentate 4,4´-bis(dimethylamino)-2,2´-bipyridine ligands (dmabpy) can catalyze ammonia oxidation to dinitrogen by reducing the overpotential of ammonia over 300 mV. Relative to the parent complex, [Ru(trpy)(bpy)(NH3)][PF6]2 (1a, bpy = 2,2’-bipyridine), substituting H at the 4 and 4´ positions of bpy with NMe2 lowered E1/2 by 350 mV. In this work, a series of Ru complexes are synthesized with phpy (2-phenyl pyridine), which bonded to the Ru metal center with the carbon and nitrogen of phenyl and pyridine rings, respectively. Because of the introduction of phpy, which is a negatively charged substituent, the net charge of the Ru complexes lowered by one in comparison with 1a and 1b complexes. In this new system, we evaluated the effects of lowering RuII/III E1/2 values by replacing bpy with an electron-donating substituent (phpy) in parent complex 1a. The structure, coordination chemistry and mechanistic implication of this new Ru chemistry in N2 evolution reactions will be discussed. Copyright by MONA MALEKA ASHTIANI 2023 For my parents who have always been the wind beneath my wings, helping me soar towards the sky of my dreams. v ACKNOWLEDGMENTS I would like to express my sincere gratitude to Prof. Smith for allowing me to work in his research laboratory and for his support throughout my Ph.D. program. I would also like to thank Prof. Hamann for his contributions and guidance, which shaped the electrochemistry part of my project. I am deeply thankful to Prof. Timothy Warren for his invaluable feedback in writing my thesis, as well as his constant support and patience during my time in graduate school. Furthermore, I extend my heartfelt appreciation to my committee members, Prof. Odom, Prof. McCusker, and Prof. O'Halloran, for their insightful comments, encouragement, and willingness to address my questions. I am particularly indebted to Dean Duxbury, Prof. Ralston, Prof. Reguera, and Prof. Dagbovie for their unwavering and continuous support during my Ph.D. I would also like to express my gratitude to Dr. Staples for his assistance in collecting X-ray crystallography data and to Dr. Holmes for his support in conducting NMR experiments and engaging in valuable data discussions. Alongside my mentors and advisors at MSU, I am immensely thankful to my dear friends and lab mates - Reza, Morteza, Alex, Pauline, Chris, Anshu, Pin, Olivia, Yu-Ling, and Tim - who fostered a friendly and productive environment, contributing to an incredible experience during my time in graduate school. I would also like to acknowledge the ammonia project team members, Dr. Quing, Dr. Miller, and Dr. Mi, for their willingness to provide assistance whenever needed. I am grateful for the funding support provided by the U.S. Department of Energy (DOE), Basic Energy Sciences (DE-SC0016604), and MSU's Graduate School. Finally, I want to express my deepest appreciation to my family, whose love and support were instrumental in my completion of this program. Thanks for always believing in me and encouraging me to pursue my dreams. vi TABLE OF CONTENTS LIST OF ABBREVIATIONS…………………………………………………………………viii Chapter 1. INTRODUCTION AND REVIEW THE PREVIOUS WORKS ON CATALYTIC AMMONIA SPLITTING REACTION .......................................................................................... 1 Chapter 2. GENERAL EXPERIMENTAL PROCEDURES ...................................................... 19 Chapter 3. CATALYTIC AMMONIA OXIDATION BY MONO-CATIONIC RU-AMMINE COMPLEXES SUPPORTED BY PHPY & TRPY LIGANDS ................................................... 26 Chapter 4. STUDY OF PLAUSIBLE INTERMEDIATES FOR AMMONIA OXIDATION; [RuIII(trpy)(phpy)(NH3)][PF6]2 & [RuII(trpy)(phpy)(N2H4)][PF6] ................................................ 53 Chapter 5. SYNTHESIS & CHARACTERIZATION OF OTHER POTENTIAL RU CATALYSTS FOR AMMONIA OXIDATION .......................................................................... 59 Chapter 6. CONCLUSION & FUTURE DIRECTIONS ............................................................ 65 Chapter 7. SYNTHESIS & CHARACTERIZATION ................................................................ 69 REFERENCES ............................................................................................................................90 APPENDIX A: FOR CHAPTER 3............................................................................................ 98 APPENDIX B: NMR, IR, UV-Vis SPECTRA……………………………………………….105 APPENDIX C: CRYSTALLOGRAOPHIC DETAILS……………………………………..121 vii LIST OF ABBREVIATIONS A Absorption Ag Elemental silver AgNO3 Silver Nitrate Ar Elemental Argon ATR Attenuated Total Reflectance B Pathlength of light, 1 cm BE Bulk Electrolysis bpy 2,2’-bipyridine C Coulomb, Concentration (M), Temperature (Celsius) CE Counter electrode cm Centimeters (1 × 10-2 meters) CO2 Carbon Dioxide CV Cyclic Voltammogram, or Cyclic Voltammetry D Diffusion Coefficient (cm2s-1) DBU 1,8-diazabicyclo [5.4.0] undec-7-ene DCM Dichloromethane DMF N, N-Dimethylformamide DMSO Dimethyl Sulfoxide dmabpy 4,4´-bis(N,N-dimethylamino)-2,2´-bipyridine e– Electron ε Molar Absorptivity (M-1 cm-1) Eo Formal Potential viii E1/2 Half-wave potential Ep Peak potential F Faraday constant (96485.3321233100184 C mol-1) Fc Ferrocene Fc+ Ferrocenium Fc* Decamethylferrocene Fc*+ Decamethylferrocenium Fe Elemental iron FOWA Foot-of-the-wave Analysis FT Fourier Transform GC Glassy Carbon H+ Free Proton H2 Molecular Hydrogen H2 O Water He Elemental Helium Ip Peak Current IUPAC International Union of Pure and Applied Chemistry J Joule K Kelvin kg Kilogram (1 × 103 grams) KPF6 Potassium hexafluorophosphate L Liters mA Milliamperes (1 × 10-3 amps) ix mL Milliliters (1 × 10-3 Liters) M Molar (moles solute divided by liters solvent) MHz Mega Hertz mM Millimolar (millimoles of solute divided by liters of solvent) MS Mass Spectrometry mV Millivolts (1 × 10-3 volts) n Integer Number of Electrons η Overpotential N2 Molecular Nitrogen NH3 Ammonia NH4+ Ammonium ion NH4OTf Ammonium trifluoromethanesulfonate NH4PF6 Ammonium hexafluorophosphate NHE Normal Hydrogen Electrode NMR Nuclear magnetic resonance NMe2-phpy 2-(3-(dimethylamino)phenyl)pyridine NMe2-trpy 4,4′,4″-tris(dimethylamino)-2,2′:6′,2″-terpyridine NO3– Nitrate Anion NHE Normal Hydrogen Electrode O2 Molecular Oxygen OH– Hydroxide Anion OTf– Trifluoromethanesulfonate anion PF6– Hexafluorophosphate anion x pH Negative base ten logarithm of the molar concentration of protons ppm Part Per Million phpy 2-phenyl pyridine Pt Elemental platinum QTOF Quadrupole Time-of-Flight RE Reference Electrode Ru Elemental ruthenium s Seconds Sat’d Saturated SWV Square Wave Voltammetry T Temperature trpy 2,2':6',2''-terpyridine TBAPF6 Tetrabutylammonium hexafluorophosphate THF Tetrahydrofuran Triflate Trifluoromethanesulfonate UV Ultraviolet V Volts Vis Visible vs. Versus WE Working Electrode XPS X-ray Photoelectron Spectroscopy °C Degrees Celsius 298.15 K DGrxn Change in Gibbs free energy for a chemical reaction at 298.15 K xi Abbreviation Chemical Structure bpy Me2N NMe2 dmabpy N N phpy N NMe2 NMe2-phpy N trpy NMe2-trpy F O F S O F O Fc*OTf Fe Fc Fe xii Chapter 1. INTRODUCTION AND REVIEW THE PREVIOUS WORKS ON CATALYTIC AMMONIA SPLITTING REACTION 1 1.1. The Importance of Carbon-free Fuels To date, fossil fuels are the main source of energy in many different sectors. This leads to the significant emission of greenhouse gases like methane (CH4) and carbon dioxide (CO2).1 According to NASA, the world climate currently holds 418 parts per million of carbon dioxide (the highest levels seen in 650,000 years).2 Figure 1.1 shows fossil fuel-related carbon dioxide emission and their social cost for different sectors in the United States (2019).a1This alarming release of CO2 gasses is a significant threat resulting in significant changes to the climate such as the thawing of permafrost in the Arctic, rising sea levels, extreme weather, and species extinction.3,4 In the United States, global warming has intensified wildfires in California, prolonged droughts in Iowa, and strengthened hurricanes both on the Eastern Seaboard and in the Gulf of Mexico. Moreover, climate change is expected to cause even more damage as time progresses, with major cities like Charleston, SC set to experience a 16-fold increase in flooding by 2045.5 Besides, the long-term effects of carbon-based fuels, specifically the public health consequences of burning fossil fuels, include respiratory illness, cancer, cardiovascular disease, and death. These health effects are immense in terms of unnecessary human suffering, and the total economic impact of health damage is estimated to be $13-29 billion each year.6 Therefore, there is a strong need to develop environmentally benign and sustainable alternatives to fossil fuels. The most effective method is the immediate decarbonization of the power grid and the developing of renewable energy conversion systems that are able to produce clean energy on demand. a1 The social cost of carbon is a measure of the economic harm caused by the emission of CO2 which express as the dollar value of the total damages. The current estimation of the social cost of carbon is over $50 per ton. 2 Figure 1.1 Fossil fuel-related CO2 emission and social cost in US for different sectors7 Societies are only able to achieve this feat by improving their ability to generate power from the sun, wind, and other renewable resources, and distribute this energy by advancing renewable energy storage systems. However, storing and distributing renewable energies like solar and wind are the main challenges in the mainstream adoption of these energies, as they are intermittent energy resources and are not constantly available and predictable. One of the approaches to this issue is carbon-free compounds that store renewable energy in their chemical bonds and supply the stored energy on demand. 1.2. Carbon-free Energy Carriers Among non-carbon-based energy carriers, hydrogen is an effective and clean alternative to the use of fossil fuels to produce energy by using fuel cells.8 Since water is the only byproduct from the combustion of hydrogen, storing solar energy in the molecular hydrogen bond (through photoelectrochemical water splitting or electrolysis) is an attractive option for researchers around the world.9,10 The disadvantage of using hydrogen gas as a fuel source is the relatively low energy density (energy per unit volume) in comparison with other potential fuels. Besides, the main challenge in the future implementation of hydrogen is its storage and transportation.11 Hydrogen’s low density makes it considerably harder to store than fossil fuels. These days, hydrogen is typically shipped in ready-to-use liquid or gas form, but the liquifying process 3 consumes 35% of its eventual energy content, and further losses occur from the inevitable boil- off in transit.12 The low density also makes hydrogen expensive to transport via roads or ships. For instance, if hydrogen were to replace natural gas in the global economy today, 3-4 times more storage infrastructure would be needed at a cost of $637 billion by 2050 to provide the same level of energy security. Nevertheless, there are other interesting compounds, such as synthetic fuels, that are not only easy to synthesize but can also be stored in a liquid form at ambient or near-ambient conditions. Among these compounds, ammonia stands out as one of the most promising options. Ammonia can store energy in the form of hydrogen to be used on demand. Ammonia splitting has several critical advantages over hydrogen technology: (i) ammonia is non-flammable and significantly safer than hydrogen. It is even safer than gasoline and propane;13 (ii) the infrastructure for the storage and transportation of ammonia already exists in the United States since it is the second largest chemical produced annually and can be stored at relatively low pressures;14 (iii) ammonia gas can be liquefied either at low pressures (around 10 atmospheres) or at room temperature and ambient pressure by mixing it with ammonium salts,15 which leads to almost three-fold larger energy density than hydrogen.16 Figure 1.2 shows an ideal carbon-free fuel cycle where energy stored in the ammonia N-H bond can be released through the ammonia splitting process. N2 and H2 are the products that are produced by ammonia splitting, which both further used up in this cycle. H2 can be fed to a hydrogen fuel cell car, combusts with O2, and generates water as a byproduct. Coupling photoelectrochemical water splitting with reduction of N2 in the NH3 synthesis would close the cycle. 4 Figure 1.2 Carbon-neutral ammonia-based fuel cycle 1.3. Ammonia Decomposition in Power Generation 1.3.1. Ammonia Decomposition in Fuel Cells Fuel cells are capable of continuously generating electricity while fueling them. Common commercialized fuel cells which differ in terms of electrolyte, fuel, and working temperature are solid oxide fuel cells (SOFC), proton exchange membrane (PEMFC), and alkaline (AFC) fuel cells.17 In AFCs ammonia does not decompose easily because of the low operation temperatures, and therefore an external reformer is necessary. However, it can tolerate ammonia concentrations of up to 9% in the hydrogen stream.18 In SOFCs which operate at high temperatures (500- 700 °C), the decomposition occurs directly at the anode.19,20 However, in addition to the need for high operating temperatures, the use of SOFC for onboard applications is limited by the poor catalyst stability, brittleness of SOFCs ceramic components, cathode poisoning, and the possibility of forming unwanted NOx byproducts.21,22,23 Ammonia supply SOFCs have been tested on a pilot scale in a 1 kW application at Kyoto University, Japan.24 In PEMFCs, any residual ammonia (an alkaline gas) damages the acidic Nafion membrane, through the formation of NH4+ ions.25,26 Also, it poisons the Pt/C anode catalyst, which 5 significantly reduces proton conductivity. Thus, the effectiveness and lifetime of the fuel cell is diminished. Therefore, PEMFCs are not suitable for ammonia. However, recently, high- temperature PEMFCs have shown a greater capacity to resist poisoning by other compounds such as CO, and they have also the potential to resist higher concentrations of ammonia.27 1.3.2. Ammonia Combustion in Engines or Gas Turbines as a Fuel Ammonia can be combusted directly in engines or gas turbines as a fuel, exploiting its high- octane number (110-130).16 The primary challenge of these technologies lies in the emission of NOx that occurs during the combustion of ammonia. The amount of NOx (nitrogen oxides) released from ammonia combustion can vary depending on several factors, including the combustion conditions, ammonia-to-air ratio, temperature, residence time, and the efficiency of emission control technologies. Initially, ammonia has been utilized in gas turbines in various forms, such as mixtures with air24 or water steam28, and in combination with other fossil fuels. This approach enables a decrease in carbon emissions while maintaining energy efficiency levels. Pilot plants in Japan, operated by IHI Corporation, have conducted tests on gas turbines directly fueled by ammonia.29 Nevertheless, the use of ammonia as a vehicle engine fuel is currently limited to prototype stages. In this regard, two possibilities have been explored: direct combustion of ammonia either by itself or in combinations, and the decomposition of ammonia to utilize the produced H2 as a fuel source onboard. Ammonia Casale Ltd. developed the first ammonia combustion engine in 1905, and it was later patented in Italy during 1935-36.30 Subsequently, in 1933, Norsk Hydro constructed a prototype vehicle featuring a hydrogen combustion engine, generated through ammonia decomposition. Another method of utilizing ammonia in a combustion engine involves mixing it with hydrogen. Research has demonstrated that ammonia mixtures containing at least 10% hydrogen by volume are highly efficient.31 In 6 2013, the Marangoni Toyota GT86-R Eco Explorer presented as a hybrid car prototype utilizes a mixture of ammonia and hydrogen as its fuel source. The hydrogen was obtained via decomposition of the same ammonia in a separate catalytic reactor utilizing the heat generated by the exhaust gases.32 1.4. Ammonia Splitting to Hydrogen and Nitrogen Thermal cracking and electrolysis are the two common approaches for ammonia splitting into hydrogen and nitrogen. 1.4.1. Thermal Cracking of Ammonia In the thermal cracking method, ammonia flows through a heterogeneous catalyst at a high temperature (400 to 800 °C) in a reactor. Ni and Ru supported on inorganic oxides and improved by various types of promoters are the most common catalysts used for this process.33,34 While Ru is the most active catalyst for ammonia decomposition at the lowest temperature (400 °C), Ni- based catalysts can yield a similar result but at a higher temperature (500-600°C) and are widely used in industry due to their lower cost.35 Because of the high price of ruthenium, other non- noble metal catalysts such as Fe, Co, or Mo can be considered an alternative for Ru-based catalysts even if they currently do not reach the activity of Ru-based catalysts.36 For ammonia decomposition, besides the active phase of the catalyst, the basicity, high conductivity, and thermal stability of support, along with the promoters play key roles in the reaction. Basicity improves the ammonia decomposition efficiency by increasing the dispersion of the active metal, enhancing ammonia dehydrogenation and desorption of surface N atoms which are the most likely rate-limiting steps of the reaction. In general, the promoters have an indirect interaction with the support, and can modulate the basicity of catalysts by increasing the electron-donating properties of the catalyst. Thus, the combination of properties like basicity and a high electron 7 donation capacity of the support and promoters are integral for the development of efficient catalysts for NH3 decomposition. Another parameter that is important in ammonia cracking systems is designing efficient reactors with different volumes. Structured reactors are superior to fixed-bed reactors in terms of portability, higher heat and mass transfer capacity, and uniform flow distribution. Despite the huge advances in developing catalysts in ammonia cracking systems, reaching practical catalytic systems still needs great effort. For having a practical ammonia decomposition system not only the type of catalyst but also the type of reactor should be considered.17 1.4.2. Electrolysis of Ammonia On the other hand, electrolysis of ammonia is an alternative that can generate on-demand hydrogen and nitrogen at room temperature. In an electrolysis cell, a potential applied between a positive (anode) and negative (cathode) electrodes while they are placed in an ammonia solution. During the electrolysis of ammonia, N2 and H2 are evolved at anode and cathode electrodes, respectively. The thermodynamic potential for ammonia electrolysis is -0.06 V, which is much lower than water electrolysis (1.23 V vs SHE). However, some additional potential is needed to drive the electrolysis called an overpotential (Figure 1.2). Mostly all studies of electrolysis of ammonia are in aqueous media. The most promising one was reported by Botte et al. in 2005.37 At the anode, the oxidation of 1 M NH3/5M KOH solution catalyzed by a Pt/Ir alloy generates 500 mAcm-2 current densities with applying 500 mV overpotential. At the cathode, Pt/Ru has been used for reducing water to H2. They reported 60% efficiency for hydrogen production under these conditions generating 400 mAcm-2 current density via applying 150 mV overpotential (Scheme 1.1) 8 Scheme 1.1 Overall reactions of ammonia electrolysis in an aqueous alkaline media Anode: 2 NH3 (aq) + 6 OH Pt/ Ir N2 (g) + 6 H2O + 6 e E = - 0.77 V (vs SHE) Pt/Ru 3 H2 (g) + 6 OH E = - 0.83 V (vs SHE) Cathode: 6 H2O + 6 e Net: 2 NH3 (aq) N2 (g) + 3 H2 (g) E = - 0.06 V (vs SHE) Due to the highly corrosive nature of alkaline media, less concentration of hydrogen, and the potential formation of NOx electrolysis of pure ammonia in a liquid state could be more favorable. The primary example of ammonia electrolysis in its liquid state was reported by Hanada et al. in 2010.38 They applied 2.0 V potential between two platinum electrodes at 9.63 bar and 25°C and achieved 7.2 mAcm-2 current density. In this electrolysis, potassium amide (KNH2, 1 M) has been used as an electrolyte which was further considered as a species oxidized at the anode and produced N2. They also attributed the generation of H2, and NH2- to the reduction of NH3 at the cathode. Although they demonstrated the generation of hydrogen and nitrogen through gas chromatography, the mechanism for this gas production was not justified. Besides, the overpotentials for these two half-reactions were not identified since only two electrodes were used. In 2015, Hamann et al. reported a more detailed study of NH3 (l) electrolysis and revised Hanada’s proposed mechanism.39 They established the two half-reactions involved in the electrolysis of liquid ammonia using Pt electrodes. At the anode, ammonia undergoes oxidation to generate NH4+ which results in poisoning the surface of the electrode and introducing an additional 500 mV overpotential in comparison with aqueous media. At the cathode, before evolving hydrogen, NH4+ species reduces to NH4• via one-electron transfer which also resulted in 9 an additional 500 mV overpotential (Scheme 1.2). They also reported a formal potential for ammonia electrolysis reaction in its liquid state which is 0.1 V vs NHE. Scheme 1.2 Overall reactions of ammonia electrolysis in a dry liquid state Anode: 4 NH3 (l) Pt 1/2 N2 (g) + 3 NH4 + 3 e E0 = 0.1 V (vs NHE) Pt 3 NH4 E0 = 0.0 V (vs NHE) 3 NH4 + 3 e Cathode: 3 NH4 Pt 3 NH3 + 3 H 3H Pt 3/2 H2 Net: NH3 (l) 1/2 N2 (g) + 3/2 H2 (g) E0 = 0.1 V (vs NHE) To reduce the kinetic overpotential, selecting an anode electrode providing a catalytic interface can be considered. As an example, Dong et al. employed an alloy of Rh-Pt-Ir as an anode electrode for reducing the overpotential of ammonia in its liquid state to 0.47 V.40 However, the performance of the electrode diminishes at higher current densities due to poisoning caused by adhering NHx species on to the surface of the electrode. This is observed in cyclic voltammetry as the current drops by successive scans (Figure 1.2). Current (A) Current (A) Over Potential Eonset Eexp Eonset Potential (V) Potential (V) Figure 1.2 Schematic representation of overpotential (left), and electrode poisoning (right) 10 An alternative for preventing the deactivation of the electrodes and facilitating the kinetics of the electrolysis process is using homogeneous catalysts dissolving in the solution of ammonia. A homogeneous catalyst is a molecular substance facilitating the electron transfer for ammonia oxidation through the bulk solution and uses electrodes as a platform of electron delivery/removal instead of involving the surface of the electrodes in bond-breaking and bond- forming electron transfer during the process of electrolysis. Besides, with these molecular systems, the steric and electronic properties of the active site for ammonia oxidation can be controlled by synthetic methods. And at the end, we can probe the mechanism involved through detailed structural and spectroscopic studies. More details and examples of these molecular systems are discussed in the next section. 1.5. Transition Metal Complexes for Ammonia Oxidation Catalysis In designing and developing molecular catalysts for ammonia oxidation reactions, the cleavage of strong N-H bonds in NH3 (BDFEN−H = 99.4 kcal/mol) and the formation of N-N bonds represent great challenges that need to be overcome.41 There are different approaches that can mediate the cleavage of N-H bonds by using transition metal complexes.42 These approaches include homolytic activation of NH3 and NH2 groups coordinated to metal center electrochemically43 or via hydrogen atom abstraction (HAA),44,45 bimetallic N-H bond activation,46 N-H oxidative addition,47 metal-ligand cooperative addition,48,49 and coordination- induced bond weakening of bonded NH3 to the metal center.50 Regarding N-N bond formation in ammonia oxidation systems, two general scenarios are considered, which include 1) coupling of two nitrogen ligands as nitride,51,52,53,54 imide, or amide,55,56 and 2) nucleophilic attack on an 57,58 electrophilic nitrido, imido, or amido ligand59 (Scheme 1.3). 11 Scheme 1.3 Proposed Pathways for N-N Bond Formation in Catalytic NH3 Oxidation bimolecular coupling [Mn] NH2 1 e oxidation H2 N [Mn] [Mn+1] NH2 - H+ nucleophilic attack [Mn] NH2 + H+ NH3 H2 N 2 e oxidation nucleophilic attack H [Mn] [Mn+2] NH [Mn] NH NH3 NH3 - 2 H+ NH2 nitride coupling [Mn] N N [Mn] 3 e oxidation [Mn+3] N -3 H+ -3H nucleophilic attack [Mn] N N [Mn+2] N NH3 NH3 Although stoichiometric oxidation of ammonia is well precedented, there are few molecular systems that have been reported to catalytically oxidize NH3 to N2.60,61,62,63,64 Some initiating work in ammonia oxidation is related to Buhr and Taube in 1979 when they reported 2+ [Os(NH3)5(CO)] as molecular complexes that oxidized ammonia both chemically and electrochemically in aqueous solution and formed μ-N2-bridged product 4+ [(Os(NH3)4(CO))2N2] .52 In 1981, Meyer and coworkers reported electrochemical oxidation of 2+ + [Ru(trpy)(bpy)(NH3)] to [Ru(trpy)(bpy)(NO2)] via a nucleophilic attack of H2O on the RuIV imido complex in an aqueous solution (Scheme 1.4).65 Although they identified the RuII-NO2 complex by spectrophotometric and cyclic voltammetry experiments, they did not isolate the RuIV-imido intermediate. 12 Scheme 1.4 Meyer’s proposed mechanism for NH3 oxidation in an aqueous solution In 1994, they reported analogous amine complexes with osmium [OsII(trpy)(bpy)NH3]2+. They showed the oxidation of OsIII-ammine by two electrons followed by rapid complex disproportionation pathways to OsII-NH3 and OsIV-NH results in N-N bond formation in the presence of a secondary amine. By exhaustive oxidation of an OsII-NH3 in the presence of excess secondary amine at pH 7.0, they isolated [OsV(trpy)(bpy)(NNR2)]3+ from electrolyzed solution. They also traped and isolated [OsIV(trpy)(bpy)(NNR2)]2+ by exhaustive reduction of [OsV(trpy)(bpy)(NNR2)]3+ at 3 V (Scheme 1.5) 66 Scheme 1.5 Meyer’s proposed mechanism for NH3 oxidation with an excess secondary amine In 2019, inspired by the 8 e- oxidation of [Ru(trpy)(bpy)(NH3)][PF6]2 (1a) where the NH3 ligand is converted to a NO3 ligand under acidic aqueous conditions, Hamann and Smith et al. envisioned that N–N bond formation would generate a hydrazine complex [Ru(trpy)(bpy)(N2H4)][PF6]2 (1h) if 1a was oxidized in the presence of NH3 under anhydrous conditions. Then subsequent oxidation of the hydrazine complex could evolve N2 and regenerate 1a to close a catalytic cycle. However, cyclic voltammetry of 1a in THF revealed a reversible peak at 1.03 V vs NHE (attributing to RuII/III redox couple), which was too positive in 13 comparison with the onset potential for noncatalytic ammonia oxidation (0.88 V vs NHE). Thus, it was ambiguous to evaluate 1a catalytic role in ammonia oxidation due to the interreference of background NH3 oxidation. Then, they focused their study to lower the E1/2 for the RuII/III redox couple to enhance their insight into the catalysis mechanism. The adjustment of electron density at the ruthenium metal center through structural alterations of the polypyridyl ligands has long been recognized as an effective method to fine-tune the catalytic activity of ruthenium polypyridyl catalysts.67,68 By incorporating electron-donating substituent groups onto the trpy and bpy moieties, the redox potential of the complex is directly influenced, consequently enhancing the accessibility of higher oxidation states of the metal and thereby impacting the catalytic activity. Previously, Berliguette et al. enhanced the efficiency and turnover frequencies (TOF) of [RuII(trpy)(bpy)OH2]2+ (as water splitting catalyst)69 by substituting electron-donating methoxy groups to the 4 and 4’ positions of bpy ligands.70 By employing the same idea, Hamann and Smith et al. changed the electronic properties of the spectator ligand through the substitution of the 4,4´-hydrogens in bipyridine (bpy) with electron-donating NMe2 groups and synthesized [Ru(trpy)(dmabpy)(NH3)][PF6]2 complex (1b). The E1/2 of RuII/III couple for 1b (0.68 V vs NHE) is 350 mV lower relative to the value for 1a and 190 mV more negative than the onset potential for NH3 oxidation on the glassy carbon electrode. Complex 1b has been shown to catalyze ammonia oxidation to dinitrogen at room temperature and ambient pressure with ca. 300 mV lower overpotential compared to the uncatalyzed oxidation at a glassy carbon electrode.57 They proposed a hydrazine/hydrazido mechanism based on Meyer’s works. In this mechanism 2 e– oxidation and proton transfer from an amine complex yield a RuIV-imido intermediate, then is disproportionate to RuII-NH3 and RuIV=NH. In the next step, a nucleophilic attack of NH3 on the imido complex results in N-N bond formation to yield a RuII-N2H4 complex. Hydrazine 14 complexes can be oxidized to their diazene counterparts, while further oxidation can generate dinitrogen and close the cycle by the loss of N2 via displacement of amine to the metal center (Scheme 1.6). Scheme 1.6 Proposed hydrazine/hydrazido mechanism for ammonia oxidation NH3 NH NH3 2+ 2+ 2+ III N IV N II N Ru N - e- Ru N Ru N - e- N N N N N 2 +H+ --H N -H+ N N N R R R R R R = H (1a) R R = H (1d) R = H (1f) R = NMe2 (1b) R = NMe2 (1e) R = NMe2 (1g) redox disproportionation NH3 N2 N NH2 NH3 N H 2N 2+ 2+ N II N II Ru N - 4 e- Ru N N N N N - 4 H+ N N R R R R R = H (1j) R = H (1h) R = NMe2 (1k) R = NMe2 (1i) Najafian and Cundari’s detailed DFT analysis also supports the originally proposed mechanism of electrocatalytic reaction mediated by [Ru(trpy)(dmabpy)(NH3)][PF6]2.71 Similarly, in 2019, Nishibayashi et al. reported catalytic chemical oxidation of ammonia, using a molecular ruthenium system with 2,2′-bpy-6,6′-dicarboxylate ligand (1c). They proposed a nitride pathway mechanism for their work based on characterizing the N2-bridged bimetallic Ru complex as the intermediate. They also observed N2 production when the Ru catalyst reacted with ammonium 15 salt in the presence of triarylaminium radical as an oxidant and 2,4,6-collidine as a base (Scheme 1.7).51 Scheme 1.7 Proposed nitride mechanism for ammonia oxidation N L N O O Ru O O L - e- 1c + N L N O O - 1/2 N2 Ru NH3 O O L L = N L 2+ + O2C N N N L N 1/2 Ru O CO2 Ru L N O O O NH3 O O N L L Ru N CO2 N L + N L N - 3 H+ O CO2 Ru - 3 e- O N L In the proposed nitride pathway, a nitride intermediate generates by consecutive 3e– oxidation and proton transfer from the metal-ammine complex. And the N-N bonds form through bimolecular coupling. The stability of nitride complexes presents a potential obstacle for the nitride pathway due to the increased energy barrier of the proposed catalytic cycle. Thus, designing a catalyst that has a lower net charge would be crucial to overcoming the barrier. 16 In recent years, homogenous (electro)catalytic ammonia oxidation has been intensively investigated through a variety of mono or bimolecular metallic systems including Ru,57,51,72,73,58,74 Fe,75,76,77 Cu.56 However, up to date, there are only a few mono-metallic Ru (electro)catalyst complexes have been reported, and some of them have been shown in Scheme 1.8. Scheme 1.8 Previously reported Ru catalysts for NH3 oxidation NH3 2+ N 2+ NH3 + N II N L N Ru N O O N IV O N Ru Ru N N II N N Ru O O N o N O N N NMe2 L o N NMe2 L = N Hamann, Smith 2019 Nishibiashi 2019 Llobet 2021 This Work Eonset (V) = 0.68 V vs NHE Eonset (V) = 0.64 V vs NHE Eonset (V) = 1.15 V vs NHE TON (t/h) = 2 TON (t/h) = 14 TON (t/h) = 7.5 The goal of this work is to evaluate the effects of i) replacing bpy with an electron-donating substituent (phpy) in parent complex [RuII(trpy)(bpy)(NH3)][PF6]2 (1a) and ii) reducing the net- charge by one in the RuII cationic compound [RuII(trpy)(phpy)(NH3)][PF6] (10) on the E1/2 of RuII/III couple and the overpotentials of ammonia oxidation. A formal carbanion is a stronger donor than an isoelectronic N lone pair which makes phpy a better donor than bpy.78 A stronger donor ligand in combination with the reduction of the net charge on the complex will make the Ru center more electron-rich; therefore, facilitating its oxidation to the higher oxidation state intermediates and stabilizing them in the N-H bond activation step. Thus, in this work, the synthesis and characterization of mono-cationic Ru catalysts that can catalyze ammonia are 17 reported. The electrochemical behavior of them has been evaluated in the absence and presence of ammonia in different solvents, supporting electrolytes, and reference electrodes. In the end, the electrochemical behavior of 10 is compared to 1a and 1b in the presence and absence of ammonia. Additionally, the synthesis of another mono-cationic Ru complex [Ru(trpy)(NMe2- phpy)NH3][PF6] (NMe2-phpy = N,N-dimethyl-3-(pyridin-2-yl)aniline (19) is shown. In this complex NH3 is placed in a trans position to the phenyl ring of phph ligand as well. This complex was characterized by 1H NMR and X-ray diffraction. The goal for the synthesis of this complex was (i) making Ru more electron rich through placing an NMe2 ligand in the para position of the phenyl ring, and (ii) comparing it with complex 10 regarding shifting the onset potential of ammonia and its substitution rate. 18 Chapter 2. GENERAL EXPERIMENTAL PROCEDURES 19 2.1. General Materials and Methods for Synthesis and Characterization All syntheses were performed under a dry, oxygen-free nitrogen atmosphere using standard Schlenk techniques. Acetonitrile and dichloromethane were dried by passing through a column of activated alumina under nitrogen. THF and pentane were dried by refluxing over sodium and benzophenone and stored under a nitrogen atmosphere.79 Ruthenium trichloride hydrate, RuCl3·xH2O, was purchased from Sigma-Aldrich (USA) or Spectrum Chemical. 2,2′:6′,2′′- Terpyridine (trpy), 97% was purchased from Alfa Aesar (USA). Tetrabutylammonium hexafluorophosphate [Bu4N][PF6] 97% was purchased from Alfa Aesar (USA) and was recrystallized from ethanol following a similar procedure used for trpy. Ammonium hexafluorophosphate 99.5% [NH4][PF6] purchased from Alfa Aesar recrystallized and dried in a vacuum oven set at 50 °C for 48 h. Phenylpyridien (phpy) purchased from Sigma-Aldrich (USA) used without further purification. Nuclear magnetic resonance (NMR) spectra were recorded on a Varian 500 MHz DD2 spectrometer equipped with a Pulsed Field Gradient (PFG) Probe. Variable temperature NMR experiments were performed on a Varian Unity Plus 500 MHz spectrometer equipped with a NALORAC 5 mm PFG probe. Crystal structures data were collected using a Bruker CCD (charge-coupled device) based diffractometer equipped with an Oxford Cryostream low-temperature apparatus operating at 173 K. CHN analyses were performed by Midwest Micro Lab (IN, USA). High-resolution mass spectra (HRMS) were obtained at the Michigan State University Mass Spectrometry Core using quadrupole time-of- flight instruments (QTOF). IR spectra were collected using a Jasco FT/IR 6600 spectrophotometer equipped with ATR PRO ONE Single-reflection ATR Accessory. 20 2.2. Electrochemistry 2.2.1. Instrument All the electrochemical experiments were conducted under an inert atmosphere using a Metrohm Autolab potentiostat. 2.2.2. Cyclic Voltammetry (CV) The CV experiments were taken in three-electrode electrochemical cells containing a counter electrode (CE), working electrode (WE), and reference electrode (RE). In all CV experiments, a glassy carbon disk electrode (surface area = 0.07 cm2) and a Pt mesh electrode have been used as working electrode, and counter electrode respectively. To obtain a reliable potential for the working electrode during a redox experiment, different customed reference electrodes have been made which their preparation will be described in the next sections. In a three-electrode configuration, WE could serve as the anode or the cathode that either oxidation or reduction reaction can occur on its surface. The type of the reaction would depend on the potential that is being set with respect to the RE. A reference electrode acts as a reference in measuring and controlling the working electrode potential without passing any current. The reference electrode should have a constant electrochemical potential at low current density. Thus, the potential at the surface of the working electrode is known since the potential difference between WE and RE is known, and the potential of the reference electrode is constant. The counter electrode in this configuration only serves the purpose of passing all the current needed to balance the current observed at the working electrode, and it will often swing to extreme potentials to accomplish this task (Figure 2.1). 21 0.015 10 mV/s Current Density (mA/cm) 2 0.010 Current (A) 0.005 0.000 -0.005 Potentiostat -0.010 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Potential (V) Potential (V vs. NHE) AUTOLAB Potential:Potential: AUTOLAB 0.5 V 0.5 V Current: 20 !A Current: 20 !A Potentiostat CE CE WE RE ground WE RE ground WE WE CE RE CE RE Gas Outlet Gas Inlet Gas Inlet Gas Outlet Electrochemical Cell Electrochemical Cell Figure 2.1 Schematic representation of a three-electrode electrochemical cell (with two side arms) used for electrochemical experiments under inert atmosphere 2.2.3. Reference Electrodes 2.2.3.1. Preparation of Ag/AgNO3 Reference Electrode A custom Ag/AgNO3 reference electrode was prepared by inserting a silver wire into the open end of a ¼ inch glass tube which was sealed on the other end with a fused Pt wire. Then the glass tube was filled with a saturated silver nitrate/methanol solution containing 0.1 M [Bu4N][PF6] as a supporting electrolyte and sealed the open end with a rubber septum (Figure 2.2). The potential of the reference electrode was measured vs. ferrocene/ferrocenium (0.095 V vs. Ag/AgNO3) in THF and then converted to NHE by adding 0.53 V.80 22 Silver wire Septum Glass tube 0.1 M TBAPF6 Methanol Pt wire Silver Nitrate Figure 2.2 Schematic representation of the custom Ag/AgNO3 reference electrode 2.2.3.2. Preparation of Fc*/ Fc*OTf Reference Electrode Fc*/Fc*+ reference electrode prepared by immersing a Pt wire into a 1/4-inch glass tube with CoralPor tip containing THF, 1 M of NH4OTf as supporting electrolyte, 3 mM of Fc*, and 6 mM of Fc*OTf. The reference electrode was prepared under an inert atmosphere and sealed properly to prevent air oxidation. The best way to prepare this reference electrode is dissolving Fc*OTf in THF with 1M NH4OTf then mixing it with Fc* that is already dissolved in pure and dry THF. 2.2.4. Controlled Potential Coulometry (CPC) To assess the catalytic activity of [Ru(trpy)(phpy)(NH3)][PF6] (10) toward ammonia oxidation CPC or Bulk Electrolysis (BE) was performed. This experiment was conducted in a 4- neck gas-tight electrochemical cell that accommodates three electrodes and one sampling port. Sampling port was kept close with a 3-layer, 1/2-inch diameter HAMILTON 76006 septum for sampling injection. A stir bar was also placed in the cell for stirring the solution during bulk electrolysis for better mass transport. Besides, the cell is equipped with two side arms for Ar gas inlet and outlets (Figure 2.3). BE performed using a 1.5 x 4.5 cm2 graphite plate working 23 electrode (dangling from a Pt wire connected to a copper wire inside a 1/4-inch diameter glass tube) with Pt mesh (connected to a copper wire), and Ag/AgNO3 as counter and reference electrodes, respectively. The top part of the glass tubes was sealed with a glue gun. For BE of ammonia in the presence of a catalyst, a constant potential at around E1/2 of the catalyst was applied to the working electrode that allows oxidation of ammonia to N2 and protons. Then the Pt mesh as a counter electrode reduces the protons and facilitates H2 evolution. Figure 2.3 The 60 mL pear-shaped electrochemical cell used in controlled potential coulometry 2.3. Product Analysis through Gas Chromatography (GC) For quantification of the final products which are N2 and H2 gases, the headspace was analyzed via gas chromatography (GC). For the GC experiment, an Agilent 7820A GC System incorporated a 30 m HP-PLOT/U column (for separating NH3 from N2 and H2), a 50 m long 5 A Molsieve column (for separating N2 from H2), and a thermal conductivity detector (TCD). The TCD can identify N2, and H2 mixed with carrier gas based on changes in the thermal conductivity of the carrier gas in the outlet. Thus, the sensitivity of different gases relies on the type of carrier gas employed. The thermal conductivity of argon and dinitrogen at 400 K are 22.6 and 32.3 (mW/mK) while for hydrogen it is 230.4 (mW/mK). That means the sensitivity of the 24 GC-TCD toward the detection of hydrogen is much higher than dinitrogen when argon is used as a carrier gas. Thus, if Ar uses as the carrier gas, the TCD sensitivity for N2 is very low due to the similar thermal conductivities of Ar and N2.39 The opposite is true for H2 detection when He uses as carrier gas. So, at the same time, the real quantity of N2, and H2 in the product cannot be detected with either Ar, or He as the carrier gas. For gas analysis, the instrument was calibrated by injection of a known volume of gaseous mixture (5% hydrogen and 95% nitrogen) to the GC (Figure 2.4). The moles of produced gases were calculated based on n = PV/RT while P is 1 atm, and T is 293 K. Figure 2.4 Gas chromatography calibration lines obtained for N2 and H2 25 Chapter 3. CATALYTIC AMMONIA OXIDATION BY MONO-CATIONIC RU-AMMINE COMPLEXES SUPPORTED BY PHPY & TRPY LIGANDS 26 3.1. Synthesis of Mono-Cationic [Ru(trpy)(phpy)(NH3)][PF6] (10) In order to evaluate the catalytic activity and electrochemical properties of mono-cationic [Ru(trpy)(phpy)(NH3)][PF6] (10), three different synthetic pathways were attempted for its preparation. In the previously reported first attempt81, Ru(III)(2,2',2"-terpyridine)Cl3 (2) was synthesized, then it was reacted with 2-phenylpyridine in DMF for 4 hours under reflux (Scheme 3.1).81 However, the desired product, [Ru(trpy)(phpy)(Cl)][PF6] (3), was produced in 3% yield instead of the reported 51%. The major product of this reaction was [Ru(trpy)(Cl)(CO)(DMF)][PF6] (4) as determined by X-ray crystallography (Figure 3.1). Scheme 3.1 Synthesis of [Ru(trpy)(phpy)(Cl)][PF6] Cl PF6 Cl 1) DMF, 4 h, reflux N Ru N N Ru N N N N N 2) TlPF6, 1 h, reflux Cl Cl 2 3 yield: 3% N O H PF6 N Ru N N Cl C O 4 Figure 3.1 Crystal structure of [Ru(trpy)Cl(CO)(DMF)][PF6] 27 CO coordination to the Ru metal center was not surprising since the reaction was refluxed in DMF for 4 hours. The DMF is the source of CO, and it decomposes in the presence of base and heat. There are some reported examples of the decarbonylation of DMF which are shown in Scheme 3.2.82,83,84 Scheme 3.2 Examples of the formation of decarbonylation of DMF Because the first attempt did not yield the desired product, a second method reported by Berlinguette and co-workers85 was tried. In this procedure, 2 was reacted with 2-phenylpyridine and N-ethylmorpholine in methanol/water solution (5:1 v/v) and refluxed for 4 hours (Scheme 3.3). After 4 hours the solution was cooled down to room temperature and then filtered. The dark purple precipitate was washed with diethyl ether (30 mL) to remove excess phpy. Solids were collected and dissolved in methanol (10 mL) and filtered to remove impurities. After filtration, solvent was removed by rotary evaporation, and the final product [Ru(trpy)(phpy)(Cl)] (5) with 28 Cl is in trans position the phenyl ring of phpy was supposed to be yielded in 24% according to the reported procedure.85 However, the 1H NMR of the final product in methanol-d4 showed two sets of isomers. In one of the isomers, Cl was trans to the phenyl ring of phpy (trans-C, reported by Berlinguette and co-workers as the sole isomer of the reaction) (5), and in the other one Cl was trans to the pyridine ring (cis-C) of phpy ligand (6) (Scheme 3.4). The later isomer (cis-C) was called impurity in Berlinguette’s work. Since this method ended up with two isomers and a low yield, a modified method was developed to isolate one isomer. In the modified method, the whole reaction and its work-up were run under a N2 atmosphere. Complex 2 was reacted with phpy, and triethylamine in methanol/water solution (5:1 v/v) and refluxed for 4 hours. After 4 hours, the precipitate was filtered and washed with cold methanol and diethyl ether. Trans-C [Ru(trpy)(phpy)Cl] (5) was obtained as a purple powder in 55% yield (Scheme 3.5). Scheme 3.3 Synthesis of [Ru(trpy)(phpy)(Cl)] with Berlinguette method85 Cl Cl methanol: water N N N 5: 1 Ru N Ru N 1.25 3 N N N 4 h, reflux Cl N O Cl 2 5 yield: 24% In the third method, phenyl pyridine was first reacted with previously reported benzene ruthenium(II) chloride dimer86 in the presence of KPF6 under basic conditions to form [Ru(phpy)(MeCN)4][PF6] (7) (Scheme 3.6).87 For further synthesis of trans-C [Ru(trpy)(phpy)(MeCN)][PF6] (8), 7 and terpyridine were refluxed for 24 h in methanol.88 Two isomers, trans-C [Ru(trpy)(phpy)(MeCN)][PF6] (8) and cis-C [Ru(trpy)(phpy)(MeCN)][PF6] (9) 29 were observed in the NMR spectrum of crude product with the ratio of 4:1, respectively (Scheme 3.7). Scheme 3.4 1H NMR of the final product from the Berlinguette method Cl Cl * * Cl Cl ** * * N N * Ru N * Ru N * * * * NN Ru NN * * * * * N N Ru N * * * N* * * * * N N * * ** * * N ** * * * * * ** * * * * * N * * * * * * * * * * 6 * * * 5 * * * Berlinguette isomer * * * * Scheme 3.5 Synthesis of trans-C [Ru(trpy)(phpy)(Cl)]; Berlinguette modification method Cl Cl methanol: water N N 5: 1 Ru N Ru N 2 8 Et3N N N N 4 h, reflux Cl N Cl 2 5 yield: 55% In complexes 8 and 9, the coordinated MeCN is in the trans and cis position to the carbon of the phpy, respectively. Since carbon is a better σ-donor than nitrogen, the Ru center is more electron-rich. Due to the trans effect, the ligand trans to the carbon is more labile and easier to be 30 replaced by other ligands. Because it is desirable to replace MeCN with NH3, only the trans-C isomer (8) was isolated and fully characterized. Scheme 3.6 Synthesis of [Ru(phpy)(MeCN)4][PF6] PF6 MeCN Cl Cl N MeCN Ru Ru + 4 KPF6 + 2 NaOH + 2 MeCN Ru Cl Cl N 20 h, 50 oC MeCN NCMe 7 yield: 68% Scheme 3.7 Synthesis of Trans-C [Ru(trpy)(phpy)(MeCN)][PF6] N PF6 N PF6 N PF6 MeCN PF6 1) MeCN/ Pentane N N N N Methanol Ru N Ru N 3:5 Ru N N N + N N MeCN Ru + N N N N 24 h, reflux 2) Excess Ether N MeCN under N2 NCMe atmosphere 7 8 9 8 yield: 60% The synthesis of trans-C [Ru(trpy)(phpy)(NH3)][PF6] (10) developed via two different routes is highlighted in Scheme 3.8. In method 1, complex 10 was synthesized through the substitution of the coordinated Cl of 5 with NH3 in water saturated with ammonia in a sealed pressure flask. This reaction was completed in 2 hours at 90 °C. The final product (10) was precipitated by addition of saturated aqueous solution of NH4PF6 in 95% yield. In method 2, acetonitrile ligand undergoes rapid replacement by NH3 in DCM saturated with ammonia. In this method, 10 was yielded in 80%. Acetonitrile rapidly displaces the NH3 ligands at ambient temperature in the absence of excess NH3; therefore, MeCN-d6 was avoided as the NMR solvent. The 1H NMR spectrum of 8 displays a single resonance at δ 2.01 ppm in DCM-d2 attributed to the protons of 31 coordinated MeCN (Appendix B, Figure B.7). Upon substitution of MeCN with NH3, the resonance at δ 2.01 ppm disappears and a singlet resonance at δ 1.26 ppm, attributed to coordinated NH3, appears in DCM-d2. A single crystal of 10 suitable for X-ray crystallography was grown by diffusion of pentane in the DCM solution of the complex. Crystal structure of complex 10 is shown in Figure 3.2. Scheme 3.8 Synthesis of trans-C [Ru(trpy)(phpy)(NH3)][PF6] with two different methods Cl NH3 PF6 N N Ru N 1) H2O/NH3, 90 oC, 2 h Ru N Method 1: N N N N 2) NH4PF6 5 10 yield: 95% N NH3 PF6 PF6 N N Ru N NH3 (Excess) Ru N Method 2: N N N N DCM 8 10 yield: 80% 32 Figure 3.2 Crystal structure of trans-C [Ru(trpy)(phpy)(NH3)][PF6] (10) 3.2. Cyclic Voltammetry of trans-C [Ru(trpy)(phpy)(NH3)]PF6 (10) For comparing the electrochemical properties of mono-cationic 10 with di-cationic 1a & 1b and investigating the effect of complex charge on the oxidation potential of Ru center and its further electrocatalytic behavior toward NH3 oxidation, it is imperative to conduct cyclic voltammetry experiments in the same condition as 1a, and 1b were taken. Thus, THF was primarily used as a solvent containing 0.1 M TBAPF6 as supporting electrolyte. The cyclic voltammogram (CV) of complex 10 was taken in a three-electrode system which includes a glassy carbon as working electrode, Pt mesh as counter electrode, and Ag/AgNO3 reference electrode. While 1a and 1b showed one reversible peak under the same conditions, complex 10 showed three anodic peaks with oxidation potentials of 0.57, 0.85, and 0.94 V vs. NHE, respectively (Figure 3.3). 33 E = 0.85 V E = 0.93 V 0.10 0.5 mM 4 in THF b 0.5 mM 4 in THF Scan rate: 100 mV/s b c Scan rate: 100 mV/s c 0.1 M TBAPF6 0.025 0.1 M TBAPF 6 Current Density (mA/cm2) Current Density (mA/cm2) 0.05 10 E = 0.55 V 0.020 a 0.00 a 0.015 -0.05 0.010 -0.10 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Potential (V vs. NHE) Potential (V vs. NHE) Figure 3.3 CV (left) and SWV (right) of 0.5 mM of 10 in THF containing 0.1 M TBAPF6 as supporting electrolyte. WE: GC, CE: Pt mesh, RE: Ag/AgNO3; scan rate: 100 mV/s For determining the nature of peaks marked as b and c in Figure 3.3, and to see if these peaks are attributed to any species adsorbed on the surface of the electrode, the CV of the complex was taken at different scan rates (Figure 3.4). 0.15 b c 10 mV/s 50 mV/s 0.10 100 mV/s Current Density (mA/cm2) 200 mV/s 300 mV/s 400 mV/s 10 0.05 a 0.00 -0.05 -0.10 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Potential (V vs. NHE) Figure 3.4 CV of 0.5 mM of 10 with different scan rates in THF with 0.1 M of TBAPF6 as supporting electrolyte; WE: Glassy carbon electrode, RE: Ag/AgNO3, and CE: Pt mesh 34 Ip in both b and c are linearly correlated with 𝜈½ confirming both peaks are under diffusion control rather than adsorption (Figure 3.5). So, this data suggested that no species were adsorbed on the surface of the electrode. Peak b Peak c 0.15 0.15 0.15 Current Density (mA/cm 2) 2) Current Density (mA/cm2) Current Density (mA/cm 0.1 0.1 0.1 y = 0.0064x + 0.0068 y = 0.0064x + 0.0068 R² = 0.999 y = 0.0064x + 0.0068 R² = 0.999 R² = 0.999 0.05 0.05 0.05 0 0 0 5 10 15 20 25 0 0 5 10 15 20 25 0 5 10 15 20 25 Square root of scan rate (V/s) Square root of scan rate (V/s) Square root of scan rate (V/s) Figure 3.5 Left: plot of current density vs square root of scan rate for peak b, Right: plot of current density vs square root of scan rate for peak c The other hypothesis that needed to be addressed was the reaction of 10 with THF. In other words, peak b can be related to the oxidation of Ru2+ to Ru 3+ and peak c can be due to the oxidation of the product of the reaction of 10 with THF. To test this hypothesis, the electrochemical experiment was conducted at two different time intervals of the same mother liquor. The mother liquor was stored in a sealed tube under inert atmosphere in the glovebox to eliminate the possibility of oxidation. As shown in Figure 3.6, peak b attributed to the oxidation of 10 is decreasing while peak c attributed to the oxidation of the THF adduct is not only increasing but also getting more reversible after keeping the complex in THF for about one month. Also, comparing the 1H NMR spectrum of 10 stayed in the THF for one month with the fresh batch of the complex in CD2Cl2 (Figure 3.7) reveals emergence of a new set of the peaks. 35 0.08 Fresh mother solution One Aftermonth a whilelater 0.06 Current Density (mA/cm2) 0.04 10 0.02 0.00 -0.02 -0.04 -0.06 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Potential (V vs. NHE) Figure 3.6 Comparison between the cyclic voltammogram of 10 in a THF solution containing 0.1 M TBAPF6 (Scan rate: 100 mV/s) at two different time intervals. WE: Glassy carbon electrode, RE: Ag/AgNO3, and CE: Pt mesh 10 10 Remain in THF for one month Figure 3.7 1H NMR of 10 in CD2Cl2 prepared freshly (Top), and after staying in THF for one month (Bottom) To test that this new set of the peaks are related to the THF adduct of 10, an attempt was made to substitute the coordinated Cl in [Ru(trpy)(phpy)Cl] (5) with THF. To do this, AgPF6 was 36 added to 10 mL THF solution of 5 and stirred for 30 min at room temperature. AgCl was filtered and the filtrate was evaporated. The final product was isolated in 30% yield and characterized as [Ru(trpy)(phpy)(THF)][PF6] (11) by 1H NMR spectroscopy and X-ray crystallography. The synthesis method of 11 is highlighted in Scheme 3.9. The single crystals of 11 suitable for X-ray crystallography were obtained by diffusion of pentane into its THF solution. 1H NMR was taken in CH2Cl2-d2 and THF-d4 (Figure 3.8). Scheme 3.9 Synthesis of trans-C [Ru(trpy)(phpy)(THF)][PF6] PF6 O Cl N N THF Ru N Ru N + AgPF6 N N N + AgCl N rt, 30 min 5 11 Yield: 30% 1 H NMR spectrum of 11 matches well with the new set of the peaks that emerge after keeping 10 in THF for prolong period of time (Figure 3.8). This clearly suggests that THF slowly substitutes NH3 in 10 at room temperature. Because THF cannot be regarded as an innocent solvent for studying the electrochemical behavior of 10, other solvents were tested for this purpose. 37 Ru_trpy_ppy_THF_in_CD2Cl2_PROTON_01 10 Remain in THF for one month PF6 O N Ru N N N 11 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 f1 (ppm) Figure 3.8 Top: 1H NMR of 10 in CD2Cl2 after staying in THF for one month; Bottom: 1H NMR of 11 in CD2Cl2 The next solvent that was used was DCM. The CV of 10 in DCM exhibited two anodic peaks at 0.6 V and 0.85 V vs NHE, while the third peak observed in THF was absent (Figure 3.9). The other test that was conducted at this step was addition of the different aliquots of THF to the DCM solution of 10 to see how CV of this complex changes. Figure 3.9 shows that by addition of various amounts of THF to the DCM solution of the complex, the third peak starts to emerge which is in consistent with substitution of NH3 by THF hypothesis. Regarding the first peak, the first hypothesis was about an impurity in the complex; however, the CHN analysis result showed it was a pure complex. Anal. Calcd for [Ru(trpy)(phpy)NH3][PF6] (10), (C26H22N5F6PRu): C, 48.00; H, 3.41; N, 10.77. Found: C, 47.81; H, 3.57; N, 10.66. 38 0.20 0.5 mMDCM 4 in DCM 0.15 Scan rate: DCM: 100THF mV/s (5:1 v/v) 0.15 DCM: THF (5: 2 v/v) 2 0.1 M TBAPF ) 2) 6 DCM: THF (5: 5 v/v) 10 Current density(mA/cm Current density (mA/cm 0.10 0.10 20 Cycles Pre-peak 0.05 0.05 0.00 0.00 -0.05 -0.05 -0.10 -0.10 -0.15 -0.15 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 -0.2 0.0 0.2Potential 0.4 (V 0.6 vs. 0.8 NHE) 1.0 1.2 1.4 Potential (V vs. NHE) Figure 3.9 Overlay the CV of 10 in DCM, and different aliquots of THF solution containing 0.1 M TBAPF6 (Scan rate: 100 mV/s), WE: Glassy carbon electrode, RE: Ag/AgNO3, and CE: Pt mesh The CV of 10 also was taken in 1,2-difluorobezene (DFB), and 1,2-dichloroethane (DCE). Figure 3.10 shows the CV of 10 in DFB, and DCE respectively. As is shown in this Figure, the pre-peak still exists at 0.5 V vs NHE in both solvents. The emergence of the pre-peak is reproducible in various solvents including THF, DCM, DFB, and DCE. Thus, another factor needs to be changed to figure the nature and source of this pre-peak. 1,2- difluorobenzene (DFB) 1,2- dichloroethane (DCE) 10 5 Pre-peak 10 Pre-peak Current ( µA) Current (!A) i (µA) 0 -5 -10 1 -0.6 1 -0.4 -0.23 5 0.0 0.27 0.49 10.61 1 1 3 5 7 9 E (V vs Ag/AgNO Potential ) (V vs NHE) 3 Potential Potential(V (Vvs vs NHE) NHE) Figure 3.10 CV of 10 in 1,2-difluorobenzene (Left), and in 1,2-dichloroethane (Right) containing 0.1 M TBAPF6 (Scan rate: 100 mV/s), WE: Glassy carbon electrode, RE: Ag/AgNO3, and CE: Pt mesh 39 To investigate the effect of supporting electrolyte on the CV of 10, NH4OTf was used instead of TBAPF6. Figure 3.11 shows the CV of 10 in THF (100 cycles) containing 0.9 M of NH4OTf as a supporting electrolyte. As is shown in Figure 3.11, there is still a pre-peak at around -0.25 V vs Ag/AgOTf. However, the ratio of the pre-peak to the main peak is much less than the other CVs with TBAPF6 electrolyte, and it doesn’t grow after 100 cycles. For comparing the two electrolytes, two different aliquots of TBAPF6 solution were added to the NH4OTf solution. Figure 3.12 shows the growth of the pre-peak with increasing concentration of TBAPF6. 10 Figure 3.11 Cyclic voltammogram of 10 (1 mM) in THF, with 0.9 M NH4OTf (Scan rate: 100 mV/s), WE: Glassy carbon electrode, RE: Ag/AgOTf, and CE: Pt disk electrode 40 10 Figure 3.12 Left: overlay the CVs of 10 with 0.9 M NH4OTf (blue), and 0.5 M TBAPF6 (black); Right: overlay the CVs of 10 with 0.9 M NH4OTf and different concentrations of TBAPF6 (0.1 M and 0.5 M); both CVs were taken in THF with scan rate of 100 mV s-1; WE: Glassy carbon electrode, RE: Ag/AgOTf, and CE: Pt disk Due to the existence of the pre-peak in CVs of 10 in the THF solution of NH4OTf even with very low intensity, we hypothesized that the PF6 counter ion of the complex may have some effects on the formation of this pre-peak. Our primary idea was about the possibility of coordination of PF6 counter ion to the Ru center and formation of different electroactive species. So, we aimed to replace the PF6 counter ion with OTf through the synthesis of [Ru(trpy)(phpy)(NH3)][OTf] (14). This complex has been made via two different methods; however, in both methods, the final product contained 10% of [Ru(trpy)(phpy)(OTf)] (15) because of the lability of coordinated NH3. The synthetic methods for 14 and 15 are described in (Appendix A, Scheme A.1). Although 14 was not isolated, CVs of the mixture of 14, and 15 (10:1) were taken in THF in the presence of NH4OTf as supporting electrolyte. As is shown in Figure 3.13, the CV and SWV of this mixture, which mainly contains 14, reveals two peaks while the pre-peak is still visible. The CV of this mixture was compared with the CV of 10 with PF6 as counter ion. Interestingly 41 the CV of both complexes showed the same peaks with the same potential vs Ag/AgOTf (Figure 3.14). Moreover, 15 was synthesized and isolated separately (Appendix A, Scheme A.3) and its CV was taken in the same condition to compare with the CV of the mixture of 14, and 15 (10:1). The reason for this experiment was to make sure if the pre-peak in the CV of the mixture was related to 15. In Figure 3.14, 15 shows two peaks which are not at the same potential as the pre- peak of 14. Since this pre-peak showed up in the CVs of both 10 and 14 with either PF6 or OTf counter ions, the other parameters had to be changed to find the pre-peak source. OTf NH3 OTf N N Ru N + Ru N N N N N 14 15 Figure 3.13 CV (left), and SWV (right) of a mixture of 14, and 15 (10:1) in THF, with 0.9 M NH4OTf (Scan rate: 100 mV/s), WE: Glassy carbon electrode, RE: Ag/AgOTf, and CE: Pt disk 42 NH3 PF6 N Ru N (10) N N 0.17 V NH3 OTf N Ru N N (14) N OTf N Ru N N (15) N 0.33 V 0.46 V Figure 3.14 Overlay the CVs (Left), and SWV (Right) of 10 (blue), 14 & 15 mixture (red), and 15 (black) containing 0.9 M NH4OTf in THF (Scan rate: 100 mV s−1); WE: Glassy carbon electrode, RE: Ag/AgOTf, and CE: Pt disk The last attempt for identifying the nature of pre-peak was trying a new reference electrode for eliminating the possibility of the reaction of 10 with Ag+ which leaks off the ion permeable tip of the silver reference electrode. The reference electrode designed for this purpose was the Fc*/Fc*+ reference electrode which completely removes silver. Fc*/Fc*+ redox couple was chosen as reference instead of Fc/Fc+ since the E1/2 of Fc was close to the E1/2 of the 10. Also, unlike Fc/Fc+, Fc*/Fc*+ was inert toward the addition of NH3 to the solution in terms of shifting the potential.89,90,91,92 Figure 3.15 shows the CV of 10 in THF with 1 M NH4OTf and the Fc*/Fc*OTf reference electrode. Cyclic voltammetry studies using a glassy carbon (GC) working electrode in THF containing 1 M of NH4OTf as the supporting electrolyte shows one II/III redox process for 10 with E1/2 of 0.404 V vs Fc*/Fc*+ attributed to the Ru redox couple (Figure 3.15), which suggests once the Ag+ is removed from the reference electrode the pre-peak will be eliminated as well. The identical intensities of the oxidation and reduction currents (Ip,c/Ip,a ≈ 1) invariant of scan rate shows that this couple is reversible under these conditions; the peak-to-peak separation (ptps) ΔEpp = 0.099 V shows Nernstian behavior. The magnitude of 43 the peak current (Ip) increases as the square root of the scan rate, which is consistent with a well- behaved, homogeneous redox couple in the solution (Figure 3.16). 10 Figure 3.15 CV of 10 (2.5 mM) in THF with 1 M NH4OTf as supporting electrolyte, and a scan rate of 100 mV/s; working, reference, and counter electrodes were glassy carbon, 6 mM Fc*/Fc*OTf and Pt mesh respectively; this data is generated by Sussanne Miller 120 100 y = 2.367x + 3.0943 R² = 0.9952 80 Current (µA) 60 40 10 20 0 0 5 10 15 20 25 30 35 40 45 Square root of scan rate (mV/s)1/2 Figure 3.16 Left: CV of 10 (2.5 mM) in THF with 1 M NH4OTf (as supporting electrolyte) at different scan rates; working, reference, and counter electrodes were glassy carbon, 6 mM Fc*/Fc*OTf, and Pt mesh respectively. Right: anodic peak current (Ip,a) of 10 vs square root of scan rates; this data is generated by Sussanne Miller The diffusion coefficient of 10 was determined using the Randles-Sevcik equation:93 44 $ % 𝑛𝐹𝜈𝐷∘ % 𝑠𝑙𝑜𝑝𝑒 𝑅𝑇 𝐼! = 0.4463𝑛𝐹𝐴𝐶 ° . 2 𝐷∘ = . 2 𝑅𝑇 0.4463𝑛𝐹𝐴𝐶 ° 𝑛𝐹 which Ip (C.s-1) is peak current, n is the number of electrons transferred in the redox event (n = 1), F is the Faradic constant (F = 96485 C.mol-1), ν is the scan rate (0.1 V.s-1), A is the electrode’s geometrical surface area (A = 0.07068 cm2), C∘ is the bulk concentration of analyte (2.5 mM = 2.5*10-6 mol.cm-3), R is the gas constant (R = 8.3145 J.K-1.mol-1), and T is the temperature (T = 295.37 K). Using this equation, the electrochemical diffusion coefficient of 10 -6 2 -1 was determined to be 2.44 × 10 cm s . 3.2.1. Comparison the CVs and E1/2 of 10 with 1b The goal of this project was comparing the E1/2 of the 10 with Ru(trpy)(dma- bpy)(NH3)][PF6]2 (1b). So, the CVs of both complexes had to be taken under the same conditions. Figure 3.17 shows the comparison of these two complexes. Figure 3.17 Overlay the CVs of 10 and 1b in THF with 1 M NH4OTf as supporting electrolyte, and a scan rate of 100 mV/s; working, reference, and counter electrodes were glassy carbon, 6 mM Fc*/Fc*OTf, and Pt mesh respectively; this data is generated by Sussanne Miller 45 As is shown in Figure 3.17, the E1/2 of mono-anionic 10 is 316 mV more negative than the one in 1b. So, lowering the net charge of the complex by introducing one negative-charged phpy ligand has a significant effect on lowering the E1/2 of the complex. The difference between the E1/2 of these two complexes was also measured in DCE vs Fc*/Fc*PF6 used as an internal standard. TBAPF6 (0.1 M) has been used as an electrolyte. Figure 3.18 shows the overlay of the CVs of these two complexes. According to the CVs, E1/2 of 10 is 380 mV lower than 1b. NH3 PF6 N Ru N N N 0.38 V lower 10 NH3 (PF6)2 N Ru N E1/2 = 0.56 V E1/2 = 0.94 V N N N NMe2 NMe2 1b Figure 3.18 Overlay the CVs of 10 (1 mM), and 1b (1 mM) in DCE with 0.1 M TBAPF6 as supporting electrolyte, and a scan rate of 100 mV/s; working, reference, and counter electrodes were glassy carbon, Ag/AgNO3, and Pt disk respectively; Fc*/Fc*PF6 (0.2 mM) was used as internal standard 3.3. Catalytic Activity of [Ru(trpy)(phpy)(NH3)][PF6] (10) toward Ammonia Oxidation In THF (Solvent), Ag/AgNO3 (RE), and TBAPF6 (Supporting Electrolyte) The next important step in this project was investigating the capability of the proposed catalyst (10) toward ammonia oxidation. To do so, the ammonia oxidation on glassy carbon electrode in the absence and presence of 10 was investigated. 46 The primary study was done in THF (solvent) with TBAPF6 as a supporting electrolyte and Ag/AgNO3 reference electrode. As shown in Figure 3.19 the onset potential of ammonia shifted approximately 400 mV to the lower potential in the presence of 10, proving a high catalytic activity of 10 toward the oxidation of ammonia. The onset potential of uncatalyzed ammonia is defined as the intersection of the baseline current with the linear portion of the oxidation wave in the J-V plot (Figure 3.19). The onset potential for non-catalyzed ammonia oxidation in THF on the surface of glassy carbon electrode is around 1.18 V vs NHE. When 0.5 mM of 10 was added to the saturated solution of ammonia (0.34 M) in THF, the ammonia oxidation potential was shifted to 0.75 V vs NHE, and the reversible peak of the complex was converted to a catalytic plateau (irreversible faradic process with loss of cathodic wave). Moreover, an enhanced current was observed for the solution containing 10 and NH3 (0.34 M) in THF with an onset potential of 0.75 V vs NHE. However, since the CV of 10 (without presence of ammonia) showed three peaks in the THF solution containing TBAPF6 with Ag/AgNO3 reference electrode, it was not the best option to evaluate its catalytic activity toward ammonia oxidation in THF. 1.4 un-catalyzed NH3 Oxidation in THF 1.4 un-catalyzed NH3 Oxidation in THF complex in THF saturated with NH3 complex in THF saturated with NH3 1.2 1.2 Current Density ( mA/cm2) complex in THF complex in THF Current Density (mA/cm2) 1.0 1.0 0.8 0.8 10 0.6 0.6 0.4 0.4 0.2 0.2 0.0 0.0 -0.2 0.75 V 1.18 V -0.2 -0.4 -0.4 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Potential (V vs. NHE) Potential (V vs. NHE) Figure 3.19 CV of 10 (blue), and ammonia oxidation with (green) and without (red) of 10. Scan rate 100 mV s−1; all solutions contain 0.1 M TBAPF6 as the supporting electrolyte. WE: glassy carbon, RE: Ag/AgNO3, and CE: Pt mesh 47 In DCE (Solvent), Ag/AgNO3 (RE), and TBAPF6 (Supporting Electrolyte) 1,2-dichloroethane (DCE) was the other solvent used to investigate the catalytic activity of 10. Figure 3.20 shows the comparison of the catalytic activity of 10 and 1b toward ammonia oxidation. In this experiment, the potentials were measured vs Fc*/Fc*+ (0.2 mM as the internal standard). The ammonia oxidation potential was lowered by 512 mV in the presence of 10 compared to 307 mV shift by 1b. So, this result shows that more electron-rich Ru centers are more effective in reducing the overpotential for ammonia electro-oxidation. Since there is still pre-peak in the CV of 10 in DCE, another solvent (DFB) has been tried for finding the catalytic activity of 10 toward ammonia oxidation. NH3 (PF6)2 N Ru N N N 512 mV 307 mV NMe2 NMe2 10 1b Figure 3.20 CV of 10 (left) and 1b (right) were taken in DCE, using TBAPF6 (0.1 M) as supporting electrolyte, with a scan rate of 100 mV s−1; WE: glassy carbon, RE: Ag/AgNO3, and CE: Pt disk; Fc*/Fc*PF6 (0.2 mM) was used as internal standard In DFB (Solvent), Ag/AgNO3 (RE), and TBAPF6 (Supporting Electrolyte) CV of 10 in DFB shows a catalytic plateau in the presence of ammonia; however, the catalytic current decreases by increasing the number of scans (50 cycles) due to poisoning of the surface of the glassy carbon electrode (Appendix A, Figure A.1, A.2). The surface of the poisoned electrode was analyzed by XPS (Appendix A, Figure A.3). 48 3.4. Evaluating the Catalytic Activity of [Ru(trpy)(phpy)(NH3)]PF6 (10) For evaluating the catalytic activity of 10, different metrics including overpotentials (η), Faradic efficiency, observed rate constants (kobs), and turnover frequency (TOF) are measured and reported. In this section, detailed descriptions of the methods by which these metrics are obtained are provided. 3.4.1. Controlled Potential Coulometry (CPC), and Product Analysis In THF (Solvent), Ag/AgNO3 (RE), and NH4PF6 (Supporting Electrolyte) CPC of 10 was investigated in THF for further detection of N2, and H2 gases as the products. Results were compared to CPC of 1b.57 In this experiment 0.1 M of NH4PF6 was used as the supporting electrolyte, graphite plate as working electrode, Pt mesh and Ag/AgNO3 as counter and reference electrodes, respectively. CPC of a 0.067 M of 10 in THF containing 0.34 M NH3 at 0.8 V (vs NHE) generates no N2 and H2 in the course of 3 hours. Unlike what was reported by Habibzadeh et al,57 NH4PF6 has very low solubility in THF even in the presence of 0.34 M ammonia. Very low concentration of NH4+ cations due to the limited solubility of NH4PF6 in THF may explain the undetectability of N2 and H2 in the headspace. In DCE (Solvent), Ag/AgNO3 (RE), and NH4OTf (Supporting Electrolyte) 1,2-dichloroetane (DCE) was chosen as the next solvent for the CPC experiment. The concentration of the saturated solution ammonia in DCE was 1.05 M which is ~3x more concentrated than THF (0.34 M) (Appendix A, Figure A.4). NH4OTf (0.1 M) was employed as a supporting electrolyte which completely dissolved in DCE. CPC of 0.067 mmol of 10 in DCE containing 1.05 M of NH3 at 0.4 V (vs Fc*0/+, which is equal to 0.8 V vs NHE) generates 0.044 mmol N2 and 0.125 mmol H2 with 67%, and 70% Faradic efficiencies during 120 minutes for 49 respective anodic and cathodic reactions (Figure 3.21). Headspace gas analysis of the CPC cell by gas chromatography revealed H2 and N2 in the molar ratio of 1: 2.8 for this duration. 350 300 250 200 charge (coulomb) 150 100 50 0 0 10000 20000 30000 40000 50000 60000 70000 80000 90000 100000 time (s) Figure 3.21 Left: The amount of the charge passed (C) during 18 h of BE by applying 0.4 V (vs. Fc*), Supporting electrolyte: 0.1 M NH4OTf, WE: graphite plate, CE: Pt mesh, RE: Ag/AgNO3; Right: Gas chromatograms (baseline corrected) from 100 µL injections of cell headspace gases before BE, during BE with no complex, and after 60, 120 min of electrolysis 3.4.2. Kinetic Parameters: Observed Rate Constants, and Turnover Frequency The overall rate of homogeneous catalysis is described by the observed rate constant (kobs), which is useful for understanding the reaction mechanism. While a detailed analysis of the six- electron/six-proton process is possible in theory, it becomes impractical in practice. Therefore, a common mechanistic approximation is to consider the simplest case scenario, where the catalyst transfers electrons to the electrode, followed by a homogeneous catalytic reaction with the substrate (NH3) EC, as shown in Scheme 3.10. This strategy has been used in the past for electrocatalytic redox processes, such as CO2 reduction94 and water oxidation95, to provide essential information about the mechanism and overall kinetics of the catalytic process. In this case, the assumption is made that electrocatalytic NH3 oxidation to N2 is triggered by a single electron transfer step that occurs at a more oxidizing potential than all other steps. If this 50 assumption is correct, it is reasonable to simplify the mechanism to an EC process, and it becomes possible to obtain a kinetic constant (kobs) that reflects the overall rate of the catalytic reaction, scaled for the number of electrons transferred (n = 6).96 Scheme 3.10 Simplified Catalytic Mechanism for Ammonia Oxidation P Q + e- kobs Q + 2 NH3 P + N2 + 6 H+ 10 and its one-electron oxidized form, [RuIII(trpy)(phpy)(NH3)][PF6] (16), are represented by P and Q, respectively. The oxidized species (Q) reacts with ammonia, ultimately leading to the release of N2. The potential for the P/Q redox couple is denoted as EP/Q, and Kobs is the apparent second-order rate constant for the catalytic chemical step. To calculate kobs, foot-of-the-wave analysis (FOWA) was utilized.94 FOW assumes that catalysis occurs under purely kinetic conditions at the foot of the wave, which can be used to analyze voltammograms that deviate from the S-shaped wave of zone KS97 due to unwanted side ! ° phenomena. When plotting I/Ip versus 1/{1 + exp [".$ (𝐸%&' − 𝐸+]}, a linear relationship is obtained for response currents under zone KS conditions (Figure 3.22). However, side phenomena cause deviation from the predicted linear relationship. At the foot of the wave, the plot adheres to the linear expectation, and a linear extrapolation can be performed to retrieve the expected linear relationship if no side phenomena had occurred. The slope of the I/Ip vs 1/{1 + ! ° 6 -1 -1 exp [".$ (𝐸%&' − 𝐸+]} plot was used to calculate kobs for 10 and was found to be 9.7×10 M s . 51 𝑅. 𝑇 𝐼 𝑛. 2.24. 3𝐹. 𝑣 . 𝑘*+, . 𝐶-° = 𝐼) 𝐹 ° 1 + exp [𝑅. 𝑇 (𝐸%&' − 𝐸+] 25 14 12 20 10 15 10 I/Ip I (µA) 8 6 10 1.7 1.5 4 1.3 5 1.1 y = 38863x + 0.6451 R² = 0.9842 2 0.9 0.7 0.000008 0.000013 0.000018 0.000023 0.000028 0 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1/[1+exp(F/R.T)(Ecat-E)] V vs NHE Figure 3.22 Left: linear sweep voltammetry (LSV) recorded at 10 mV in a THF solution containing 0.5 mM [Ru(trpy)(phpy)(NH3)][PF6] (10), 0.34 M NH3, and 0.1 M TBAPF6. Red trace shows the data range employed for performing the FOWA. Right: FOWA for an EC calculated from the previous linear sweep voltammetry recorded at 10 mV/s in THF solution containing 0.5 mM 10, 0.34 M NH3, and 0.1 TBAPF6. Ecat was determined as the potential at which the electrocatalyst undergoes a mechanistically relevant redox process in the absence of substrate (ammonia) 52 Chapter 4. STUDY OF PLAUSIBLE INTERMEDIATES FOR AMMONIA OXIDATION; [RuIII(trpy)(phpy)(NH3)][PF6]2 & [RuII(trpy)(phpy)(N2H4)][PF6] 53 [RuIII(trpy)(dmabpy)(NH3)][PF6]2 (1d) and [RuII(trpy)(dmabpy)(N2H4)][PF6] (1h) have been previously reported as possible intermediates in electrocatalyzed ammonia oxidation.57 In this chapter the synthesis and characterization of the corresponding species, [RuIII(trpy)(phpy)(NH3)][PF6]2 (17) and [RuII(trpy)(phpy)(N2H4)][PF6] (18) will be discussed. Moreover, the electrochemical behavior of these complexes has been investigated by cyclic voltammetry in the following sections. 4.1. Reaction of [RuII(trpy)(phpy)NH3][PF6] with a Non-coordinating Base CV of 10 in 1,2-difluorobenzene (DFB) has been monitored during the addition of 1,8- diazabicyclo[5.4.0]undec-7-ene (DBU) as a non-coordinating base. The CV of this solution containing 0.5 mM of 10 and 0.13 mM DBU exhibits new redox features as shown in Figure 4.1. In this figure, the CV of 10 has been shown before and after the addition of DBU. By addition of DBU to 10, the RuIII-NH3 species generated electrochemically on the surface of electrode by sweeping the potential, got involved in another redox process to possibly generate RuIV=NH species via losing two protons and two electrons. It is also shown that the return wave of 10 attributed to the reduction of RuIII to RuII has disappeared, which suggests that Ru(III)-NH3 is the first intermediate generated electrochemically under catalytic conditions. However, to get a better insight into the redox product of RuIII-NH3 with DBU and in turn the mechanism of the reaction, [RuIII(trpy)(phpy)NH3][PF6]2 (17) was synthesized independently to study its reaction with NH3 or a noncoordinating base. The generation of intermediates can be monitored via variable temperature 1H NMR spectroscopy. 54 15 N 10 + N DBU 10 5 Current (µA) 0 -5 -10 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 Potential (V vs NHE) Figure 4.1 CVs of a solution of 0.5 M 10 in DFB before (orange) and after (blue) addition of 0.13 mM DBU. Scan rate 100 mVs-1. Conditions: 0.1 M TBAPF6 supporting electrolyte; WE: glassy carbon, CE: Pt mesh, RE: Ag/AgNO3 4.2. Synthesis and characterization of [RuIII(trpy)(phpy)NH3][PF6]2 (17) For synthesis of [RuIII(trpy)(phpy)NH3][PF6]2 (16), 1 equiv of tris(para-bromophenyl) ammonium cation radical, [N(pBr-ph)3]PF6 was added to 1 equiv of 10 in DCM. After 30 min of stirring under nitrogen at room temperature, [Ru(trpy)(phpy)NH3][PF6]2 (17) precipitated as a green solid. The precipitate was collected on a fine frit and rinsed several times with fresh DCM. The yield of the reaction was 83% (Scheme 4.1). 1H NMR of 17 in MeCN-d3 shows broad peaks in the chemical shift range of -109 to 36 ppm, which is characteristic of paramagnetic Ru(III) complexes. 55 Scheme 4.1 Synthesis of [RuIII(trpy)(phpy)(NH3)][PF6]2 (17) Br NH3 PF6 NH3 (PF6) (PF6)2 N N Ru N RuIII N N + Br N N N N DCM, 30 min Br 10 17 yield: 83% 4.3. Synthesis of [Ru(trpy)(phpy)(N2H4)][PF6] (18) The synthesis [Ru(trpy)(phpy)N2H4][PF6] (18) via two different methods is shown in Scheme 4.2. In the first method, [Ru(trpy)(phpy)Cl] (5) was dissolved in excess hydrazine monohydrate and refluxed for 30 minutes. [Ru(trpy)(phpy)N2H4][PF6] (18) was isolated as dark purple solid in 45% yield via precipitation by addition of an aqueous saturated solution of NH4PF6. In the second method, [Ru(trpy)(phpy)MeCN][PF6] (8) was dissolved in dichloromethane and then hydrazine/THF solution was added to the reaction flask. The solution was stirred for 1 h at room temperature. After that, the volume of the solution was reduced to 5 mL, and then diethyl ether was added to the solution. [Ru(trpy)(phpy)N2H4][PF6] (18) was obtained as a dark purple solid in 78% yield. The single crystal suitable for X-ray crystallography was obtained by diffusion of diethyl ether in the dichloromethane solution of the complex. Coordinated N2H4 displays two resonances at 3.76 and 2.70 ppm in its corresponding 1H NMR spectrum in dichloromethane-d2 (Appendix B, Figure B.22). 56 Scheme 4.2 Two different methods for synthesis of [Ru(trpy)(phpy)(N2H4)][PF6] (18) Method 1: H 2N Cl NH2 PF6 N 1) N2H4 (in THF), reflux 1 h N Ru N Ru N N N N N 2) NH4PF6 5 18 yield: 45% Method 2: H 2N NH2 PF6 N PF6 N excess N2H4 (in THF) N Ru N Ru N N CH2Cl2, rt, 1 h N N N 8 18 yield: 78% 4.4. Cyclic Voltammetry of [Ru(trpy)(phpy)(N2H4)][PF6] (18) The electrochemical behavior of 0.5 mM of 18 was evaluated by cyclic voltammetry (CV) in THF containing 0.1 M of TBAPF6 as the supporting electrolyte and GC as the working electrode (Figure 4.1). The CV of 18, exhibits one reversible wave with anodic and cathodic peaks at 0.90 and 0.79 V, respectively, and a peak-to-peak separation of 0.11 V at E1/2 = 0.83 V vs NHE. The CV of the complex was also taken in the presence of ammonia (0.34 M) in THF solution. Interestingly, a catalytic plateau was observed at an onset potential of 0.75 V vs NHE, which matches with the catalytic plateau onset obtained for [Ru(trpy)(phpy)(NH3)][PF6] in the presence 57 of ammonia. These results suggest that the coordinated N2H4 ligand may be as and intermediate enroute on the oxidation of coordinated NH3 to N2 and H2. 1.4 un-catalyzed NH3 Oxidation in THF H 2N NH2 PF6 complex in THF saturated with NH3 1.2 N Ru N Current Density ( mA/cm2) complex in THF N 1.0 N 0.8 0.6 18 0.4 0.2 0.0 -0.2 -0.4 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Potential (V vs. NHE) Figure 4.1 Overlay the CV of [Ru(trpy)(phpy)(N2H4)][PF6] (17) without (blue) and with ammonia (red) in THF containing [NBu4][PF6] (0.1 M); Scan rate: 100 mV s−1; WE: glassy carbon, RE: Ag/AgNO3, and CE: Pt mesh 58 Chapter 5. SYNTHESIS & CHARACTERIZATION OF OTHER POTENTIAL RU CATALYSTS FOR AMMONIA OXIDATION 59 For making the Ru center more electron rich and thus shifting the oxidation potential of the complex to more negative E1/2 values, phpy ligand with electron donating NMe2 group was utilized on the synthesis of [Ru(trpy)(NMe2-phpy)(NH3)][PF6] (20). 5.1. Synthesis of [Ru(trpy)(NMe2-phpy)(NH3)][PF6] (20) The synthesis of 2-(3-(dimethylamino)phenyl)pyridine (NMe2-phpy) is highlighted in Scheme 5.1. In the first step, 2-(3-aminophenyl)pyridine was prepared by a literature procedure.98,99 To a suspension of 2-bromopyridine (2 equiv), 3-aminophenyl boronic acid (1 equiv), potassium carbonate, and tetrakis(triphenylphosphine) palladium [Pd(PPh3)]4 in THF, degassed water was added. The mixture was refluxed under nitrogen at 75 °C for 72 hours. After 72 hours, the solvent was evaporated, and the crude product was extracted by ethyl acetate (3*50 mL). MgSO4 was added to the ethyl acetate solution to remove the remaining water and then filtered. In the end, an oily liquid remained as a crude product. Then pentane/ ethyl acetate (40 mL: 20 mL) was added and some of the impurities were precipitated. The product was further purified by flash chromatography on a silica gel column with pentane/ethyl acetate (2:1). In the second step, N,N,N-trimethyl-3-(pyridin-2-yl)benzenaminium was prepared. NaH (4 equiv) dispersed in oil (60%) was added to dry THF under streaming of N2 gas. Then the flask was placed in an ice bath for 10 min. After which 2-(3-aminophenyl)pyridine (NH2-phpy) dissolved in THF was added to the flask while it was placed in an ice bath. Then MeI (10 equiv) was added to the flask while it was in the ice bath. After 15 minutes, it was brought out from the ice bath and let it reach room temperature while it was stirring. The solution was heated up to 60 0C for 2 hours. When it started to reflux, the color changed to oily yellow with solid made around it. After that, when the solution was cooled down to room temperature, 2 equiv of water 60 (0.5 mL) was added to the solution to neutralize all the extra NaH. Then 50 mL more THF was added (since by adding water probably some of MeI dissolved). The solution was filtered to remove the precipitate. N,N,N-trimethyl-3-(pyridin-2-yl)benzenaminium salt, which was slightly soluble in CDCl3 was obtained as a white powder in 100% yield. In the third step, 2-(3-(dimethylamino)phenyl) pyridine was prepared by modification of two literature procedures.100,101 N,N,N-trimethyl-3-(pyridin-2-yl) benzeneaminium (NMe3-phpy) (2 equiv) was added to Cs2CO3 (1 equiv) in toluene. Then 2-naphthol (1.5 equiv) was added to the solution and heated up for 2 hours at 110 °C. When the solution cooled down to room temperature, the mixture was washed with HCl 1 M. After that, the solution was stirred for 10 minutes, and then 50 mL water was added. The desired product is in the organic layer. Thus, the toluene was removed, and the residue was dissolved in a 1:1 solution of ethyl acetate/hexane to precipitate the impurity. Then, the precipitate was filtered, and the solvent was removed from the filtrate using a rotavapor, a brown oil remained. For purifying the final product, a silica column was run using 80:20 v/v hexane: ethyl acetate as eluent. 2-(3-(dimethylamino)phenyl) pyridine (NMe2-phpy) was obtained as yellow oil in 20% yield (Scheme 5.1). For synthesis of [Ru(trpy)(NMe2-phpy)Cl] (19), [Ru(trpy)Cl3] (2), NMe2-phpy, and triethylamine (TEA) were dissolved in water: methanol (1:5 v/v) and added to a 250 mL Schlenk flask under nitrogen. The mixture was refluxed at 80 °C for 4 h. After which the solution was cooled down to room temperature and a deep purple precipitate was made. The resulting solution was filtered by the fritted funnel and washed with diethyl ether (100 mL) and cold methanol (10 mL). The product was placed under a vacuum overnight to be dried. [Ru(trpy)(NMe2-phpy)Cl] was obtained as purple powder in 18% yield. The crystal structure was taken by diffusion of diethyl ether in the dichloromethane solution of the complex (Scheme 5.2). 61 Scheme 5.1 Synthesis of 2-(3-(dimethylamino)phenyl) pyridine NH2 HO OH B Pd(PPh3)4 (0.38 mmol) Step 1: K2CO3 in water N Br N NH2 THF yield: 85% I N NH2 NaH (4 eq) MeI (10 eq) Step 2: N N THF reflux, 2 h yield: 100% I N N OMe OH Step 3: Cs2CO3 N N Toluene, 2 h reflux yield: 20% For the synthesis of ammonia 2(3-dimethylamino) phenyl pyridine terpyridine ruthenium(II) hexafluorophosphate, [Ru(trpy)(NMe2-phpy)NH3][PF6] (20), [Ru(trpy)(NMe2-phpy)Cl (19) was added to 40 mL of water saturated with ammonia in a pressure flask and heated up for 1 hour at 90 °C. After 1 hour, 10 mL of DI water saturated with ammonium hexafluorophosphate NH4PF6 was added to the solution and the final product was precipitated. The precipitate was filtered by the fritted funnel, washed with diethyl ether (30 mL), and placed under a vacuum overnight to be dried. [Ru(trpy)(NMe2-phpy)NH3][PF6] was obtained as a purple powder in 63% yield. The crystal structure was taken by diffusion of pentane in the dichloromethane solution of the complex (Scheme 5.3). 62 Scheme 5.2 Synthesis of trans-C [Ru(trpy)(NMe2-phpy)Cl] (19) Cl N Cl methanol: water N N 5: 1 Ru N Ru N Et3N N N N Cl 4 h, reflux @ 80 oC Cl N N 2 19 yield: 18% Scheme 5.3 Synthesis of trans-C [Ru(trpy)(NMe2-phpy)(NH3)][PF6] (20) NH3 PF6 Cl N N Ru N Ru N 1) H2O/NH3, reflux 1 h N N N N 2) NH4PF6 N N 19 20 yield: 63% The 1H NMR of [Ru(trpy)(NMe2-phpy)NH3][PF6] (20) shows that the ammonia detached from the Ru center after a while (almost 1 month) (Figure 5.1). This data shows that NH3 in 20 is very labile than NH3 in trans-C [Ru(trpy)(phpy)NH3][PF6] (10). Thus, the next step in this study involves assessing the electrochemical behavior of this complex in the absence and presence of ammonia with the intention of comparing it to 10. 63 Bonded-NH3 Ru_trpy_NMe2-ppy_NH3@0degree_PROTON_01 11.0 10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -0.5 f1 (ppm) 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 f1 (ppm) Figure 5.1 Comparison of 1H NMR of [Ru(trpy)(NMe2-phpy)NH3][PF6] in CD2Cl2 freshly prepared (top), and remained for one month in solid state in glovebox (bottom) 64 Chapter 6. CONCLUSION & FUTURE DIRECTIONS 65 This work is built on the development of Ru-bipyridine complexes that reduce the overpotential for ammonia splitting by over 300 mV. Here the effect of reducing charge of Ru- polypyridyl complexes on shifting catalytic current is investigated. Electron donating substituents such as NMe2 on bpy or trpy will stabilize high oxidation states of Ru. An alternative way for electronically tuning bpy-complex is to replace the bpy ligand with 2- phenylpyridine (phpy). A formal carbanion is a stronger donor than an isoelectronic N lone pair that makes phpy a better donor than bpy. A stronger donor ligand in combination with the reduction of the net charge on the complex will make the Ru center more electron rich therefore facilitating its oxidation. In this work, we report the synthesis and characterization of mono-cationic Ru(II)-ammine complexes as catalysts for ammonia oxidation which supported by a phpy and trpy ligands. The electrochemical behavior of these complexes has been evaluated in the absence and presence of ammonia using cyclic voltammetry methods. Also, the effect of charge reduction versus electron donation on the overpotential of ammonia splitting is investigated. The catalytic behavior was confirmed via electrochemical studies and the products of the ammonia splitting, N2, and H2, were quantified via controlled potential colometry (bulk electrolysis) in presence of [Ru(trpy)(phpy)NH3][PF6]. Those results confirmed that the onset of the oxidation of NH3 was reduced by approximately 600 mV upon addition of the catalyst and N2 and H2 were generated with ratios of approximately 1: 3, with Faradaic efficiencies as high as 70%. Since the solution after the electrolysis, only contained the starting [Ru(trpy)(bpy)NH3][PF6] catalyst after 120 min of electrolysis, it was concluded that the catalyst regeneration was fully achieved, and a closed catalytic cycle was performing. The possibility of heterogeneous catalysis is unlikely given that no N2 and H2 were detected in control rinse test experiments. Next, understanding of the 66 mechanism of the catalysis was pursued via intermediate studies. The [RuIII(trpy)(phpy)NH3][PF6]2 intermediate was isolated and was further studied using a variety of techniques including 1H NMR and electrochemical measurements. It was shown that the [RuIII(trpy)(bpy)NH3][PF6]2 complex was the first intermediate under catalytic conditions where the applied potential is positive to enable the one electron oxidation of the Ru(II) center to Ru(III). Electrochemical experiments revealed that [RuIII(trpy)(phpy)NH3][PF6]2 is unstable intermediate in the presence of a proton acceptor and undergoes deprotonation to give a [RuIV(trpy)(phpy)NH][PF6] intermediate that was not directly detected. However, since the hydrazine pathway for the catalytic cycle was previously established, the generation of the RuIV=NH intermediate was still envisioned to be a key step in the reaction mechanism. This was further studied in experiments which were conducted using an authentic RuII-N2H4 complex. The cyclic voltammograms of solutions of the hydrazine complex were closely comparable to the CVs of solutions of [Ru(trpy)(phpy)NH3][PF6] and NH3 in THF. Cyclic voltammograms of the saturated solution of NH3 in THF in the presence of [Ru(trpy)(phpy)N2H4][PF6] exhibited a catalytic current with an onset identical to that obtained when [Ru(trpy)(phpy)NH3][PF6] was used as the catalyst. As a future direction, more experiments including 15NH3 isotope labeling can be envisioned for the characterization of the possible intermediates en route to intramolecular N–N coupling of catalytic NH3 oxidation. The bulk electrolysis experiment will be redone using a glassy carbon electrode instead of a graphite electrode for two reasons. Firstly, the porosity of graphite makes it difficult to use XPS to determine the possibility of catalyst deposition on its surface. Secondly, the lower overpotential of ammonia oxidation on the graphite electrode compared to the glassy carbon electrode can cause the electrocatalytic current of the oxidation potential to overlap with 67 the background current. By using the glassy carbon electrode, we aim to address these issues and advance the accuracy and reliability of the experimental results. Electron microscopy studies of the electrode surfaces after catalysis would test for the presences of any nanoparticulate ruthenium deposits. Besides, to make Ru center more electron efficient and therefore shift the oxidation potential of the catalyst to less anodic potentials, phpy ligand was functionalized by NMe2 group. Thus, the future goal is calculating the substitution rate of labeled 15NH3 with bonded NH3 in these two complexes and evaluating the electrochemical behavior of this complex in the absence and presence of ammonia. 68 Chapter 7. SYNTHESIS & CHARACTERIZATION 69 7.1. Synthesis of [Ru(trpy)(phpy)NH3][PF6] (10) 10 was synthesized through 2 different methods described below. Method 1: 10 was synthesized in three steps as described below: 7.1.1. Synthesis of (2,2 ́:6 ́,2 ́ ́-terpyridyl) trichloro ruthenium(III), [Ru(trpy)Cl3] (2) Cl N Ru N N Cl Cl This complex was prepared by a literature procedure and characterized by ESI+-MS: m/z: 404.9 [M-Cl+].102 RuCl3•3 H2O (498 mg, 1.91 mmol) along with trpy ligand (446 mg, 1.91 mmol), and ethanol (125 mL) were added to a round bottom flask containing a magnetic stir bar. The solution was refluxed at 78 °C for 3 h, after which the solution was cooled down to room temperature. The resulting solution was filtered by fritted funnel, washed with 3 ×30 mL portion of absolute ethanol followed by 3×30 mL diethyl ether. The product was placed under vacuum overnight to be dried. [Ru(trpy)Cl3] was obtained as brown solids in 88% yield (740 mg, 1.67 mmol). 7.1.2. Synthesis of (2,2 ́:6 ́,2 ́ ́-terpyridyl) (2-phenylpyridine) chloro ruthenium(II), [Ru(trpy)(phpy)Cl] (5) Cl N Ru N N N 70 This complex was synthesized by modification of a method reported by Berlinguette et al.85 [Ru(trpy)Cl3] (700 mg, 1.95 mmol), phenylpyridine (0.282 mL, 1.98 mmol), and triethylamine (TEA) (1.63 mL, 11.7 mmol) were dissolved in water: methanol (1:5 v/v, 122 mL) and added to a 250 mL Schlenk flask under nitrogen. The mixture was refluxed at 77 °C for 4 h. After which the solution was cooled down to room temperature and a deep purple precipitate was made. The resulting solution was filtered by fritted funnel, washed with diethyl ether (100 mL) and cold methanol (10 mL). The product was placed under vacuum overnight to be dried. Trans-C [Ru(trpy)(phpy)Cl] was obtained as purple powder in 55% yield (457 mg, 0.87 mmol). 1H NMR (500 MHz, Methylene Chloride-d2) δ 10.33 (d, J = 5.5 Hz, 1H), 8.18 (d, J = 8.0 Hz, 2H), 8.11 (d, J = 8.1 Hz, 2H), 8.06 (d, J = 8.1 Hz, 1H), 7.88 (t, J = 7.8 Hz, 1H), 7.77 – 7.70 (m, 3H), 7.65 (q, J = 7.2, 6.8 Hz, 3H), 7.47 (t, J = 6.6 Hz, 1H), 7.12 (t, J = 6.5 Hz, 2H), 6.59 (t, J = 7.3 Hz, 1H), 6.38 (t, J = 7.4 Hz, 1H), 5.71 (d, J = 7.8 Hz, 1H). Uv-Vis spectrum of this complex in DCM between 400-700 nm shows two significant peaks @ 423 nm and 567 nm. 7.1.3. Synthesis of (2,2 ́:6 ́,2 ́ ́-Terpyridyl) (2-phenylpyridine) ruthenium(II) ammine hexafluoro phosphate, [Ru(trpy)(phpy)NH3][PF6] (10) NH3 PF6 N Ru N N N [Ru(trpy)(phpy)Cl (1 g, 1.9 mmol) was added to 150 mL of water saturated with ammonia in a pressure flask and heated up for 2 hours at 80 °C. After which the solution was cooled down to the room temperature and filtered under N2 atmosphere to remove all the unreacted starting material. Then NH4PF6 (340 mg, 2 mmol) was added to the filtrate and the final product was precipitated. The precipitate was filtered by fritted funnel, washed with water (30 71 mL) and diethyl ether (60 mL) successively, and placed under vacuum overnight to be dried. [Ru(trpy)(phpy)NH3][PF6] was obtained as purple powder in 95% yield (977 mg, 1.5 mmol). 1H NMR (500 MHz, Methylene Chloride-d2) δ 9.08 (dt, J = 5.6, 1.2 Hz, 1H), 8.23 (d, J = 8.0 Hz, 2H), 8.18 – 8.10 (m, 3H), 7.94 (td, J = 7.8, 1.5 Hz, 1H), 7.85 (t, J = 8.0 Hz, 1H), 7.79 – 7.71 (m, 4H), 7.65 (dd, J = 7.8, 1.3 Hz, 1H), 7.55 (ddd, J = 7.2, 5.6, 1.4 Hz, 1H), 7.19 (ddd, J = 7.0, 5.7, 1.4 Hz, 2H), 6.63 (td, J = 7.5, 1.3 Hz, 1H), 6.44 (td, J = 7.3, 1.3 Hz, 1H), 5.75 (dd, J = 7.6, 1.2 Hz, 1H), 1.26 (s, 3H, NH3). 13C NMR (126 MHz, Methylene Chloride- d2) δ 165.14, 157.94, 157.59, 151.02, 149.27, 145.49, 135.42, 134.60 (d, J = 9.7 Hz), 128.51, 127.58, 126.94, 123.39, 122.41 (d, J = 7.8 Hz), 121.27, 120.14, 119.08. Combustion analyses. Calculated for C26H22F6N5PRu, C, 47.96; H, 3.40; N, 10.75. Found: C, 47.81; H, 3.57; N, 10.66. Uv-Vis spectrum of 10 (0.05 mM) in DCM between 200-700 nm shows two significant peaks @400 nm and 520 nm. 7.2. Method 2: 10 was synthesized in three steps as described below: 7.2.1. Synthesis of benzeneruthenium(II) chloride dimer, [(ƞ6-C6H6)RuCl(µ-Cl)]2 Cl Cl Ru Ru Cl Cl This complex was prepared by a literature procedure.86 1,3-cyclohexadiene (6 mL, 62 mmol) was added to RuCl3•3H2O (1.7 g, 6.5 mmol) in ethanol/ water (90: 10 v/v). The solution was refluxed under nitrogen at 45°C for 3 h, after which the volume was reduced to 30 mL by rotovap under the air. The resulting solution was filtered by fritted funnel, washed with ethanol, 72 and dried under vacuum. [(ƞ6-C6H6)RuCl(µ-Cl)]2 was obtained as red-brown solids in 87% yield (1.4 g, 2 mmol). 1H NMR (500 MHz, DMSO-d6) δ 5.97 (s, 12 H). 7.2.2. Synthesis of tetrakisacetonitrile phenyl pyridine ruthenium(II) hexafluorophosphate, [Ru(phpy)(MeCN)4][PF6] (7) MeCN PF6 N MeCN Ru MeCN NCMe This complex was prepared by a literature procedure.103 [(ƞ6-C6H6)RuCl(µ-Cl)]2 (1.5 g, 3.01 mmol) and 2-phenylpyridine (phpy) (860 µL, 6.02 mmol) were added to 100 mL Schlenk flask. NaOH (240 mg, 6.02 mmol) was dissolved in minimal amount of MeCN and was heated to 30 °C for 2 minutes then added to the reaction. KPF6 (2.22 g, 12.04 mmol) was dissolved in a minimal amount of MeCN and then added to the reaction flask. MeCN (50 mL) was added as solvent. The solution was refluxed and stirred at 50 °C for 20 h. The resulting yellow slurry was evaporated to dryness under reduced pressure via rotovap. Residue solid was purified by column chromatography on neutral Al2O3 using MeCN as eluent. The yellow band was collected and evaporated to dryness by rotavapor in the air. The yellow powder was dissolved in a mixture of CH2Cl2: MeCN (1:1 v/v) and was purified by recrystallization in diethyl ether (600 mL). [Ru(phpy)(MeCN)4][PF6] was obtained as yellow solid in 68% yield (1.15 g, 2 mmol). Single crystals of this complex obtained by a slow diffusion of diethyl ether into a concentrated solution of the yellow solid in a mixture of CH2Cl2:MeCN (1:1 v/v). 1H NMR (500 MHz, Acetonitrile-d3) δ 8.88 (dd, J = 5.8, 1.4 Hz, 1H), 7.94 (d, J = 7.4 Hz, 1H), 7.85 (d, J = 8.1 Hz, 1H), 7.73 (d, J = 1.6 Hz, 0H), 7.73 – 7.67 (m, 2H), 7.13 (ddd, J = 7.2, 5.6, 1.4 Hz, 1H), 7.06 (td, J = 7.3, 1.4 Hz, 1H), 6.92 (t, J = 7.4 Hz, 1H), 2.49 (s, 3H, NCCH3), 2.12 (s, 2H, NCCH3), 1.94 (s, 3H, NCCH3). 73 7.2.3. Synthesis of acetonitrile phenyl pyridine terpyridine ruthenium(II) hexafluorophosphate, trans-C [Ru(trpy)(phpy)MeCN][PF6] (8) N PF6 N Ru N N N This complex was prepared by a literature procedure.88 [Ru(phpy)(MeCN)4][PF6] (300 mg, 0.53 mmol), terpyridine (120 mg, 0.53 mmol), and anhydrous methanol (15 mL) were added to 50 mL Schlenk flask under nitrogen. The mixture was refluxed at 70 °C for 24 h. During which time the color changed from yellow to deep purple. The mixture was cooled, filtered through cannula filter. The solvents were removed under vacuum. At this stage the crude product consisted in a mixture of cis and trans in a 1:4 ratio. In glove box it was dissolved in the minimum amount of MeCN/pentane (8 mL, 3: 5 v/v) from which solution of product (trans-C) was obtained by adding an excess of Et2O (600 mL). Trans-C [Ru(trpy)(phpy)MeCN][PF6] was obtained as purple powder in 60% yield (213 mg, 0.31 mmol). 1H NMR (500 MHz, Acetonitrile-d3) δ 9.49 (d, J = 5.6 Hz, 1H), 8.39 (dt, J = 8.2, 1.8 Hz, 2H), 8.28 (d, J = 8.1 Hz, 2H), 8.18 (d, J = 8.2 Hz, 1H), 7.98 (tdd, J = 7.9, 6.0, 1.7 Hz, 2H), 7.81 (tt, J = 7.7, 1.7 Hz, 2H), 7.73 – 7.66 (m, 3H), 7.54 (ddt, J = 7.3, 5.6, 1.6 Hz, 1H), 7.22 (ddt, J = 7.4, 5.8, 1.7 Hz, 2H), 6.64 (td, J = 7.4, 1.7 Hz, 1H), 6.46 (ddt, J = 7.4, 5.7, 1.7 Hz, 1H), 5.73 (dd, J = 7.6, 1.8 Hz, 1H), 1.94 (s, 3H). 7.2.4. Synthesis of ammonia phenyl pyridine terpyridine ruthenium(II) hexafluorophosphate, trans-C [Ru(trpy)(phpy)NH3][PF6] (10) 74 NH3 PF6 N Ru N N N Trans-C [Ru(trpy)(phpy)MeCN][PF6] (200 mg, 0.296 mmol) and dichloromethane (10 mL) was added to 50 mL Schlenk flask. Then excess amount of ammonia (5 equiv, 1.49 mmol) condensed into the reaction’s vessel. After the reaction came to the room temperature, liquid ammonia reacted with the reactant quickly and the color of solution changed to dark purple. After 30 minutes, diethyl ether (1000 mL) was added, and the trans- C [Ru(trpy)(phpy)NH3][PF6] was obtained in 80% yield (154 mg, 0.23 mmol). Crystallization from dichloromethane/pentane gave deep purple crystals, which were found to be suitable for X-ray analyses. 1H NMR (500 MHz, d2-dichloromethae) δ 9.09 (d, J = 5.5 Hz, 1H), 8.24 (d, J = 8.0 Hz, 2H), 8.14 (dd, J = 8.5, 5.0 Hz, 3H), 7.95 (t, J = 7.8 Hz, 1H), 7.86 (t, J = 7.9 Hz, 1H), 7.80 – 7.71 (m, 4H), 7.66 (d, J = 7.8 Hz, 1H), 7.61 – 7.50 (m, 1H), 7.24 – 7.14 (m, 2H), 6.65 (t, J = 7.5 Hz, 1H), 6.45 (t, J = 7.3 Hz, 1H), 5.77 (d, J = 7.4 Hz, 1H), 5.34 (d, J = 6.1 Hz, 1H), 1.26 (s, 3H, NH3). 75 7.3. Synthesis of [Ru(trpy)(phpy)NH3][OTf] (14) 14 was synthesized through 2 different methods described below. 7.3.1. Method 1: Synthesis of (2,2 ́:6 ́,2 ́ ́-Terpyridyl) (2-phenylpyridine) ruthenium(II) ammine triflate, [Ru(trpy)(phpy)NH3][OTf] (14) from [Ru(trpy)(phpy)(Cl)] (5) NH3 OTf N Ru N N N [Ru(trpy)(phpy)Cl (591 mg, 1.12 mmol) was added to 150 mL of water saturated with ammonia in a pressure flask and heated up for 2 hours at 90 °C. After which the solution was cooled down to the room temperature and filtered under N2 atmosphere to remove all the unreacted starting material. Then NH4OTf (190 mg, 1.13 mmol) was added to the filtrate and the final product was precipitated. The precipitate was filtered by fritted funnel, washed with water (30 mL) and diethyl ether successively (60 mL), and placed under vacuum overnight to be dried. [Ru(trpy)(phpy)NH3][OTf] was obtained as purple powder alongside with a side product turned out to be [Ru(trpy)(phpy)(OTf)], (15) by taking 19F NMR @ -30 °C from final product. The ratio of 14 to 15 is 10:1 in the 1H NMR. The yield of 14 is 52% (380 mg, 0.58 mmol). 1H NMR of final product shows two sets of the peaks relating to 14 and 15. For 14 1H NMR (500 MHz, Methylene Chloride-d2) δ 9.23 (d, J = 5.5 Hz, 1H), 8.23 (s, 2H), 8.12 (t, J = 8.8 Hz, 3H), 7.93 (t, J = 7.8 Hz, 1H), 7.84 (d, J = 8.0 Hz, 1H), 7.79 – 7.70 (m, 4H), 7.64 (d, J = 7.8 Hz, 1H), 7.59 – 7.54 (m, 1H), 7.18 (d, J = 13.2 Hz, 1H), 6.63 (t, J = 7.3 Hz, 1H), 6.43 (t, J = 7.2 Hz, 1H), 5.74 (d, J = 7.9 Hz, 1H), 1.45 (s, 3H). For 14 1H NMR (500 MHz, Methylene Chloride-d2) δ 9.54 (d, J = 5.6 Hz, 1H), 8.14 (d, J = 8.0 Hz, 2H), 8.07 (dd, J = 14.0, 8.1 Hz, 3H), 7.94 – 7.87 (m, 1H), 7.82 (t, J = 8.0 Hz, 1H), 7.72 – 7.61 (m, 5H), 7.49 (t, J = 6.6 Hz, 1H), 7.16 (dd, J = 7.5, 5.5 Hz, 2H), 76 19 6.43 (q, J = 8.9 Hz, 2H), 5.57 (s, 1H). F NMR of the mixture including 14 and 15 at room temperature (471 MHz, Methylene Chloride-d2) shows a broad single peak at δ -79.03 ppm. However, the 19F NMR for the same compound shows two peaks at δ -79.15 and -79.74 at -30 °C. 7.3.2. Method 2: 14 was synthesized in three steps as described below: 7.3.2.1. Synthesis of tetrakisacetonitrile phenylpyridine ruthenium(II) triflate, [Ru(phpy)(MeCN)4][OTf] (12) OTf N NCMe Ru MeCN NCMe NCMe [(ƞ6-C6H6)RuCl(µ-Cl)]2 (500 mg, 1 mmol) and 2-phenylpyridine (phpy) (286 µL, 2 mmol) were added to 100 mL Schlenk flask. NaOH (80 mg, 2 mmol) was dissolved in minimal amount of MeCN and was heated to 30 °C for 2 minutes then added to the reaction. KOTf (752.68 mg, 4 mmol) was dissolved in a minimal amount of MeCN and then added to the reaction flask. MeCN (20 mL) was added as solvent. The solution was refluxed and stirred at 50 °C for 20 h. The resulting yellow slurry was evaporated to dryness under reduced pressure via rotovap. Residue solid was purified by column chromatography on neutral Al2O3 using MeCN as eluent. The yellow band was collected and evaporated to dryness by rotavapor in the air. The yellow powder was dissolved in a mixture of CH2Cl2: MeCN (1:1 v/v) and was purified by recrystallization in diethyl ether (600 mL). [Ru(phpy)(MeCN)4][OTf] was obtained as yellow solid in 69% yield (732 mg, 1.28 mmol). Single crystals of this complex obtained by a slow diffusion of diethyl ether into a concentrated solution of the yellow solid in a mixture of CH2Cl2: 77 MeCN (1:1 v/v). 1H NMR (500 MHz, Acetonitrile-d3) δ 8.90 (dt, J = 5.5, 1.1 Hz, 1H), 7.96 (dd, J = 7.5, 1.2 Hz, 1H), 7.88 (dd, J = 8.2, 1.2 Hz, 1H), 7.78 – 7.70 (m, 2H), 7.15 (ddd, J = 7.2, 5.6, 1.4 Hz, 1H), 7.08 (td, J = 7.3, 1.3 Hz, 1H), 6.95 (td, J = 7.4, 1.3 Hz, 1H), 2.51 (s, 3H), 2.01 (s, 6H), 1.96 (s, 3H). 7.3.2.2. Synthesis of acetonitrile phenylpyridine terpyridine ruthenium(II) triflate, trans-C [Ru(trpy)(phpy)MeCN][OTf] (13) N OTf N Ru N N N [Ru(phpy)(MeCN)4][OTf] (700 mg, 1.22 mmol), terpyridine (280 mg, 1.2 mmol), and anhydrous methanol (50 mL) were added to 100 mL Schlenk flask under nitrogen. The mixture was refluxed at 70 °C for 24 h. During which time the color changed from yellow to deep purple. The mixture was cooled, filtered through cannula filter. The solvents were removed under vacuum. At this stage the crude product consisted in a mixture of cis and trans. In glove box it was dissolved in the minimum amount of MeCN/pentane (16 mL, 3: 5 v/v) from which solution of product (trans-C) was obtained by adding an excess of Et2O (600 mL). Residue solid was purified by column chromatography on neutral Al2O3 using MeCN as eluent. The purple band was collected and evaporated to dryness by rotavapor in the air. Then, the purple powder was dissolved in a minimal of MeCN and was purified by recrystallization in diethyl ether (600 mL). Trans-C [Ru(trpy)(phpy)MeCN][OTf] was obtained as purple powder in 55% yield (458 mg, 0.67 mmol). Crystallization from acetonitrile/ether gave deep purple crystals, which were found 78 to be suitable for X-ray analysis. 1H NMR (500 MHz, Acetonitrile-d3) δ 9.49 (d, J = 5.5 Hz, 1H), 8.39 (d, J = 8.0 Hz, 2H), 8.28 (d, J = 8.1 Hz, 2H), 8.18 (d, J = 8.2 Hz, 1H), 7.98 (q, J = 7.8 Hz, 2H), 7.81 (td, J = 7.8, 1.5 Hz, 2H), 7.69 (d, J = 6.6 Hz, 3H), 7.54 (ddd, J = 7.2, 5.7, 1.4 Hz, 1H), 7.22 (ddd, J = 7.3, 5.6, 1.4 Hz, 2H), 6.69 – 6.59 (m, 1H), 6.46 (td, J = 7.3, 1.3 Hz, 1H), 5.73 (dd, J = 7.6, 1.2 Hz, 1H), 1.96 (s, 3H). 19F NMR (471 MHz, Methylene Chloride-d2) δ -79.35. 7.3.2.3. Synthesis of (2,2 ́:6 ́,2 ́ ́-Terpyridyl) (2-phenylpyridine) ruthenium(II) ammine triflate, [Ru(trpy)(phpy)NH3][OTf] (14) from [Ru(trpy)(phpy)MeCN][OTf] (13) NH3 OTf N Ru N N N [Ru(trpy)(phpy)MeCN][OTf] (50 mg, 0.07 mmol) was added to 10 mL of 1,2- dichlororthane (DCE) saturated with ammonia in a pressure flask and heated up for 2 hours at 90 °C. After which the solution was cooled down to the room temperature. Then diethyl ether (200 mL) was added to the solution, and the final product was precipitated. The precipitate was filtered by fritted funnel, washed with water and diethyl ether successively, and placed under vacuum overnight to be dried. In this method like a previous one [Ru(trpy)(phpy)NH3][OTf] (14) was obtained as purple powder alongside [Ru(trpy)(phpy)(OTf)] (15) complex. The ratio of 14 to 15 is 10:1 according to the 1H NMR. The yield of 12 is 79% yield (40 mg, 0.06 mmol). 79 7.4. Synthesis of (2,2 ́:6 ́,2 ́ ́-Terpyridyl) (2-phenylpyridine) ruthenium(II) triflate, [Ru(trpy)(phpy)(OTf)] (15) OTf N Ru N N N [Ru(trpy)(phpy)MeCN][OTf] (601 mg, 0.88 mmol) was added to 10 mL of dichloromethane (DCM) in a 25 mL round bottom flask and the solution stirred for 3 h in RT. After which the solvent was removed, and the remaining residue was recrystallized in DCM/ Ether for two times. The precipitate was filtered by fritted funnel, washed with diethyl ether, and placed under vacuum overnight to be dried. [Ru(trpy)(phpy)(OTf)] was obtained as purple powder in 60% yield (341 mg, 0.53 mmol). The single crystal which was suitable for X-ray crystallography was obtained by diffusion of diethyl ether in dichloromethane. 1H NMR (500 MHz, Methylene Chloride-d2) δ 9.54 (d, J = 5.6 Hz, 1H), 8.14 (d, J = 8.0 Hz, 2H), 8.07 (dd, J = 14.0, 8.1 Hz, 3H), 7.94 – 7.87 (m, 1H), 7.82 (t, J = 8.0 Hz, 1H), 7.72 – 7.61 (m, 5H), 7.49 (t, J = 6.6 Hz, 1H), 7.16 (dd, J = 7.5, 5.5 Hz, 2H), 6.43 (q, J = 8.9 Hz, 2H), 5.57 (s, 1H). 13C NMR (151 MHz, Methylene Chloride-d2) δ 163.80, 159.35, 158.76, 151.41, 149.81, 135.68, 135.09, 134.88, 128.70, 127.33, 126.73, 123.38, 122.51, 122.08, 121.03, 118.76, 66.15, 15.56. 19F NMR (471 MHz, Methylene Chloride-d2) δ -79.41. 7.5. Synthesis of [Ru(trpy)(NMe2-phpy)NH3][PF6] (20) 20 was synthesized through the following steps as described below: 80 7.5.1. Synthesis of 2-(3-aminophenyl)pyridine H 2N N This ligand was prepared by a literature procedure.98,99 To a suspension of 2- bromopyridine (6.32 g, 40 mmol), 3-aminophenylboronic acid (3 g, 20 mmol), potassium carbonate (4 g, 28 mmol), and tetrakis(triphenylphosphine) palladium [Pd(PPh3)]4 (430 mg, 0.38 mmol) in 50 mL THF under N2 flow, degassed water (50 mL) were added. The mixture was refluxed under nitrogen at 75 °C for 72 hours. After 72 hrs, the solvent was evaporated, and the crude product was extracted by ethyl acetate (3*50 mL). MgSO4 was added to the ethyl acetate solution to remove the remaining water and then filtered. At the end an oily liquid remained as a crude product. Then pentane/ ethyl acetate (40 mL: 20 mL) were added and some of impurities were precipitated. Then a silica column was run with pentane/ ethyl acetate (2:1) as eluent and the final product was purified. (Note: the final product has a white color in column, and it is the second dot on TLC plate with 0.35 rf). 1H NMR (500 MHz, Chloroform-d) δ 8.68 (dt, J = 3.6, 1.6 Hz, 1H), 7.85 – 7.62 (m, 2H), 7.40 (q, J = 2.0 Hz, 1H), 7.36 – 7.31 (m, 1H), 7.30 – 7.26 (m, 1H), 7.23 (td, J = 5.7, 2.2 Hz, 1H), 6.76 (dtd, J = 7.9, 2.4, 1.0 Hz, 1H), 3.76 (s, 3H). 7.5.2. Synthesis of N,N,N-trimethyl-3-(pyridin-2-yl)benzenaminium 81 NaH (1.88 g, 4 equiv) dispersed in oil (60%) was added to a 3-neck round bottom flask (100 mL) and placed under streaming of N2 gas for 30 minutes. Then dry THF (20 mL) was transferred to the flask under N2 atmosphere, and the flask was placed in an ice bath for 10 minutes. After which 2-(3-aminophenyl)pyridine (NH2-phpy) (2 g, 11 mmol) dissolved in THF was added to the flask while it placed in an ice bath. For 1 hour it was stirred to let all the gases remove. Then MeI (7.28 mL, 16.6 g, 10 equiv) was added to the flask while it was in the ice bath. For 15 minutes it was in an ice bath and stirred. After that it is brought out from the ice bath and let reach room temperature while it is stirring. Then the solution was heated up to 60 0C for 2 hours. When it started to reflux, the color changed to oily yellow with solid made around it. After 2 hours refluxing, when the solution reached room temperature, 2 equiv of water (0.5 mL) was added to the solution to neutralize all the extra NaH. Then 50 mL more THF was added (since by adding water probably some of MeI dissolved). The solution was filtered to filter the precipitate. N,N,N-trimethyl-3-(pyridin-2-yl)benzenaminium salt which was slightly soluble in CDCl3 was obtained as white powder in 100% yield (4.14 g, 11 mmol). 1H NMR (500 MHz, Chloroform-d) δ 8.67 (ddd, J = 4.8, 1.8, 0.9 Hz, 1H), 8.54 (dd, J = 2.9, 1.4 Hz, 1H), 8.17 (ddd, J = 8.4, 2.9, 0.8 Hz, 1H), 8.13 (dt, J = 7.9, 0.9 Hz, 1H), 8.05 (dt, J = 8.0, 1.1 Hz, 1H), 7.84 (td, J = 7.7, 1.8 Hz, 1H), 7.72 (t, J = 8.1 Hz, 1H), 7.31 (ddd, J = 7.6, 4.8, 1.1 Hz, 1H), 4.10 (s, 9H). 7.5.3. Synthesis of 2-(3-(dimethylamino)phenyl)pyridine N N 82 This ligand was prepared by modification of two literature procedures.100,101 N,N,N- trimethyl-3-(pyridin-2-yl)benzenaminium (NMe3-phpy) (4.7 g, 13.82 mmol) was added to Cs2CO3 (1.95 g, 5.52 mmol) in 92 mL toluene. Then 2-naphtol (1.32 g, 9.2 mmol) was added to the solution and heated up for 2 hours at 110 °C. When the solution cooled down to R.T, the mixture was washed with HCl 1 M (12 mL, 12 mmol). After that, the solution stirred for 10 minutes, and then 50 mL water was added. The desired product is in organic layer. Thus, the toluene was removed, and the residue was dissolved in 1:1 solution of ethyl acetate/hexane to precipitate the impurity. Then, the precipitate was filtered, and the solvent was removed from the filtrate using a rotavapor, a brown oil remained. For purifying the final product, a silica column was run using 80:20 v/v hexane: ethyl acetate as eluent. 2-(3- (dimethylamino)phenyl)pyridine was obtained as yellow oil in 20% yield (550 mg, 2.77 mmol). 1H NMR (500 MHz, Chloroform-d) δ 8.70 (dt, J = 4.8, 1.4 Hz, 1H), 7.82 – 7.69 (m, 2H), 7.44 (dd, J = 2.7, 1.6 Hz, 1H), 7.35 (t, J = 7.9 Hz, 1H), 7.29 (dt, J = 7.6, 1.3 Hz, 1H), 7.21 (td, J = 4.8, 3.8 Hz, 1H), 6.82 (ddd, J = 8.3, 2.7, 1.0 Hz, 1H), 3.03 (s, 6H). 7.5.4. Synthesis of (2,2 ́:6 ́,2 ́ ́-terpyridyl) 2(3-dimethylamino) phenylpyridine chloro ruthenium(II), [Ru(trpy)(NMe2-phpy)Cl] (19) Cl N Ru N N N N [Ru(trpy)Cl3] (568 mg, 1.27 mmol), 2(3-dimethylamino) phenylpyridine (320 mg, 1.6 mmol), and triethylamine (TEA) (1.36 mL, 9.75 mmol) were dissolved in water: methanol 83 (1:5 v/v, 117 mL) and added to a 250 mL Schlenk flask under nitrogen. The mixture was refluxed at 80 °C for 4 h. After which the solution was cooled down to room temperature and a deep purple precipitate was made. The resulting solution was filtered by fritted funnel, washed with diethyl ether (100 mL) and cold methanol (10 mL). The product was placed under vacuum overnight to be dried. [Ru(trpy)(NMe2-phpy)Cl] was obtained as purple powder in 18% yield (130 mg, 0.22 mmol). The crystal structure was taken by diffusion of diethyl ether in dichloromethane solution of the complex. 1H NMR (500 MHz, Methylene Chloride-d2) δ 10.32 (ddd, J = 5.6, 1.6, 0.8 Hz, 1H), 8.15 (d, J = 7.9 Hz, 2H), 8.08 (dt, J = 8.2, 1.2 Hz, 2H), 8.03 (dt, J = 8.1, 1.1 Hz, 1H), 7.86 (ddd, J = 8.1, 7.3, 1.7 Hz, 1H), 7.76 (ddd, J = 5.6, 1.5, 0.8 Hz, 2H), 7.67 (t, J = 7.9 Hz, 1H), 7.62 (ddd, J = 8.1, 7.4, 1.5 Hz, 2H), 7.44 (ddd, J = 7.2, 5.7, 1.4 Hz, 1H), 7.15 (d, J = 2.7 Hz, 1H), 7.10 (ddd, J = 7.2, 5.7, 1.4 Hz, 2H), 6.07 (dd, J = 8.4, 2.6 Hz, 1H), 5.49 (d, J = 8.3 Hz, 1H), 2.68 (s, 6H). 7.5.5. Synthesis of ammonia 2(3-dimethylamino)phenylpyridine terpyridine ruthenium(II) hexafluorophosphate, trans-C [Ru(trpy)(NMe2-phpy)NH3][PF6] (20) NH3 PF6 N Ru N N N N [Ru(trpy)(NMe2-phpy)Cl (80 mg, 0.141 mmol) was added to 40 mL of water saturated with ammonia in a pressure flask and heated up for 1 hours at 90 °C. After 1 hour, 10 mL of DI water saturated with ammonium hexafluorophosphate NH4PF6 was added to the solution and the final product was precipitated. The precipitate was filtered by fritted funnel, washed with diethyl ether (30 mL), and placed under vacuum overnight to be dried. [Ru(trpy)(NMe2-phpy)NH3][PF6] 84 was obtained as purple powder in 63% yield (62 mg, 0.08 mmol). The crystal structure was taken by diffusion of pentane in dichloromethane solution of the complex. 1H NMR (500 MHz, Methylene Chloride-d2) δ 9.06 (d, J = 5.6 Hz, 1H), 8.20 (d, J = 8.0 Hz, 2H), 8.13 (d, J = 8.1 Hz, 2H), 8.09 (d, J = 8.4 Hz, 1H), 7.94 (t, J = 7.8 Hz, 1H), 7.82 (t, J = 8.0 Hz, 1H), 7.78 – 7.66 (m, 4H), 7.51 (t, J = 6.3 Hz, 1H), 7.19 (t, J = 6.6 Hz, 2H), 7.09 (s, 1H), 6.07 (s, 1H), 5.49 (s, 1H), 2.78 (t, J = 112.8 Hz, 5H), 1.20 (s, 3H). 19F NMR (470 MHz, Methylene Chloride-d2) δ -72.79 (d, J = 711.4 Hz). Combustion analyses. Calculated for C26H27F6N6PRu, C, 49.9; H, 4; N, 11.39. Found: C, 50.01; H, 4.31; N, 11.25. 7.6. Synthesis of other ruthenium polypyridyl complexes 7.6.1. Synthesis of (2,2´:6´,2´´-Terpyridyl) (2-phenylpyridine) chloro ruthenium(II) hexafluorophosphate, [Ru(trpy)(phpy)Cl][PF6] (3) Cl PF6 N Ru N N N This complex was prepared by a literature procedure.81 [Ru(trpy)Cl3] (440 mg, 1 mmol), and phenylpyridine (0.142 mL, 1 mmol) were dissolved in DMF (20 mL). The mixture was refluxed at 155 °C for 4 h. After which TlPF6 (700 mg, 2 mmol) was added to the mixture and the reaction was refluxed for one more hour. After that the solution was cooled down in a freezer overnight and then the solution was filtered by fritted funnel. Diethyl ether (600 mL) was added to the filtrate and the crude product was precipitated. Then the crude product was purified by weakly acidic alumina column with acetonitrile/ toluene (1: 2 v/v) as eluent. The first band was purple that followed by green band and an orange band. The green band relating to the 85 [Ru(trpy)(phpy)Cl][PF6] which was reported in the literature in 51% yield; however, according to the three times experiments runed by the author of this thesis, the final product was obtained in 3% yield (22.83 mg, 0.029 mmol). Calculated for [Ru(trpy)(phpy)Cl][PF6]•Toluene (C33H27F6N4PClRu): C, 52.08; H, 3.58; N, 7.36. Found: C, 52.34; H, 3.84; N, 7.26. Interestingly, most of the products were in purple band and orange band characterized by X-ray spectroscopy. The crystal structures of purple band and orange band were taken by diffusion of toluene in acetonitrile solution of these complexes. They purple band was turned out to be trans- [Ru(trpy)(CO)(Cl)(NCMe)]PF6 and the orange band was cis-C [Ru(trpy)(CO)(Cl)(NCMe)]PF6. 7.6.2. Synthesis of phenylpyridine terpyridine tetrahydrofuran ruthenium(II) hexafluorophosphate, trans-C [Ru(trpy)(phpy)(THF)][PF6] (11) PF6 O N Ru N N N [Ru(trpy)(phpy)Cl] (50 mg, 0.095 mol) and AgPF6 (24.07 mg, 0.095 mmol) were added to 10 mL THF in 25 mL round bottom flask and stirred for 30 min under N2 atmosphere. At the end, the precipitate which was AgCl was filtered by fritted funnel and the filtrate was evaporated. The final product which was [Ru(trpy)(phpy)(THF)][PF6] was isolated in 30% yield (20 mg, 0.028 mmol). The color of product was dark purple. The crystal structure was obtained by diffusion of pentane in THF solution of the complex. 1H NMR (500 MHz, THF-d8) δ 9.24 (s, 1H), 8.51 (d, J = 8.0 Hz, 2H), 8.42 (d, J = 8.0 Hz, 2H), 8.22 (d, J = 8.1 Hz, 1H), 7.98 (td, J = 8.0, 4.3 Hz, 2H), 7.85 (t, J = 7.7 Hz, 2H), 7.72 (d, J = 5.5 Hz, 2H), 7.65 (d, J = 7.8 Hz, 2H), 7.27 (t, J = 6.6 Hz, 86 2H), 6.50 (d, J = 8.5 Hz, 1H), 6.32 (t, J = 7.4 Hz, 1H), 5.65 (d, J = 7.9 Hz, 1H), 3.64 – 3.60 (m, 17H), 1.80 – 1.75 (m, 17H). 19F NMR (470 MHz, THF-d8) δ -73.60 (d, J = 710.2 Hz). 7.6.3. Synthesis of {[RuIII(trpy)(phpy)]2(𝜇-O)}[OTf]2 Complex (16) (OTf)2 N N N N Ru O Ru N N N N This product was made when DCM solution of [Ru(trpy)(phpy)(NH3)][OTf] (10 mg, 0.015 mmol, 0.03 M) exposed to the air. The color of complex is purple however, when it exposed to the air, it turned to the brown. The single crystal of this complex was obtained when the solvent completely evaporated. The {[RuIII(trpy)(phpy)]2(𝜇-O)}[OTf]2 was obtained when all the solvent is gone in 60% yield (6 mg, 0.004 mmol). 1H NMR (500 MHz, Methylene Chloride-d2) δ 34.80 (s, 1H), 22.65 (s, 1H), 21.65 (s, 1H), 18.85 (s, 1H), 13.80 (s, 1H), 12.64 (s, 2H), 12.06 (s, 2H), 7.37 (s, 2H), -5.64 (s, 2H), -7.63 (s, 2H), -9.10 (s, 1H), -22.58 (s, 1H), -47.13 (s, 1H), -57.28 (s, 1H). 19F NMR (470 MHz, Methylene Chloride-d2) δ -77.74. 7.6.4. Synthesis of (2,2 ́:6 ́,2 ́ ́-Terpyridyl) (2-phenylpyridine) ruthenium(III) ammine hexafluoro phosphate, [RuIII(trpy)(phpy)NH3][PF6]2 (17) NH3 (PF6)2 N RuIII N N N Tris(para-bromophenyl) ammonium cation radical, [N(pBr-ph)3][PF6] (47.4 mg, 0.076 mmol) as a chemical oxidant was added to the solution of [Ru(trpy)(phpy)NH3][PF6] (50 mg, 0.076 mmol) in DCM yielded a green precipitate after 30 min of stirring under nitrogen. The 87 solid was collected on a fine glass filter and was rinsed several times with fresh DCM. The [RuIII(trpy)(phpy)NH3][PF6]2 was obtained as final product with yield of 83% (50 mg, 0.062). 1 H NMR (500 MHz, MeCN-d3) δ 36.82, 36.17, 22.55, 12.49, 12.26, 8.08, 1.29, -4.94, -14.98, - 18.46, -21.80, -24.17, -26.72, -74.11, -109.69. 7.6.5. Synthesis of hydrazine phenylpyridine terpyridine ruthenium(II) hexafluorophosphate, trans-C [Ru(trpy)(phpy)N2H4][PF6] (18) H 2N NH2 PF6 N Ru N N N Method 1: [Ru(trpy)(phpy)Cl] (400 mg, 0.59 mmol) was dissolved in excess hydrazine monohydrate (10 mL) in a 25 mL Schlenk flask and refluxed for 30 minuets. After which water saturated with NH4PF6 was added to the solution and trans-C [Ru(trpy)(phpy)N2H4][PF6] was precipitated as dark purple solid in 45% yield (177 mg, 0.26 mmol). Method 2: Trans-C [Ru(trpy)(phpy)MeCN][PF6] (100 mg, 0.148 mmol) was dissolved in dichloromethane (17 mL) and then was added to 100 mL Schlenk flask. After which hydrazine solution in THF (6 mL of 0.1 M) was added to reaction flask. The solution stirred for 1 h in RT then the volume of solution reduced to 5 mL after which, diethyl ether (500 mL) was added to the solution. Trans-C [Ru(trpy)(phpy)N2H4][PF6] was obtained as dark purple solid in 78% yield (77 mg, 0.11 mmol). The crystal structure was taken by diffusion of diethyl ether in dichloromethane solution of the complex. 1H NMR (500 MHz, d2-dichloromethane) δ 9.53 (d, J = 5.4 Hz, 1H), 8.25 (d, J = 8.3 Hz, 2H), 8.17 – 8.13 (m, 2H), 8.12 (d, J = 8.1 Hz, 1H), 7.94 (td, J 88 = 7.9, 1.6 Hz, 1H), 7.88 (t, J = 8.1 Hz, 1H), 7.76 (td, J = 8.0, 1.6 Hz, 2H), 7.74 – 7.71 (m, 2H), 7.65 (d, J = 7.8 Hz, 1H), 7.58 – 7.53 (m, 1H), 7.20 (dd, J = 7.4, 5.7 Hz, 2H), 6.64 (t, J = 6.9 Hz, 1H), 6.46 – 6.41 (m, 1H), 5.74 (d, J = 7.6 Hz, 1H), 5.32 (d, J = 1.2 Hz, 1H), 3.76 (s, 2H), 2.70 (s, 2H). 89 REFERENCES (1) Jackson, R. B.; Le Quéré, C.; Andrew, R. M.; Canadell, J. G.; Korsbakken, J. I.; Liu, Z.; Peters, G. P.; Zheng, B. Global Energy Growth Is Outpacing Decarbonization. Environ. 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This reaction was completed in 2 hours at 90 °C. Then, the final product (14) was precipitated by NH4OTf in 52% yield. However, alongside 14, 15 has been made with the ratio of 10:1. 15 has been determined 19 through a FNMR @ -30 °C from the final product. In method 2, acetonitrile ligand in [Ru(trpy)(phpy)(MeCN)][OTf] (13) was replaced with NH3 at room temperature rapidly in presence of the DCE solution saturated with ammonia. In this method, 14 was yielded in 79% alongside with 15 (Scheme A.1). Although 14 results from an air free atmosphere, it should be noted that it becomes fully oxidized to{[RuIII(trpy)(phpy)]2(𝜇-O)}[OTf]2 (16) if the DCM solution of 14 is exposed to the air (Scheme A.2). In 1H NMR of this complex taken in CD2Cl2, the singlet NH3 peak that appeared at 1.47 ppm is gone, and trpy and phpy hydrogens appear in paramagnetic regions ranging from -60 to 40 ppm. The brown single crystal of this complex was obtained by slow evaporation of DCM. Moreover, 15 was synthesized separately by dissolving [Ru(trpy)(phpy)MeCN][OTf] in 10 mL of DCM and stirred for 3 h in RT, which the solvent was removed and the remaining residue was recrystallized in DCM/ether for two times. The precipitate was filtered using a fritted funnel, washed with diethyl ether, and placed under vacuum overnight to be dried. [Ru(trpy)(phpy)(OTf)] was obtained as purple powder in 60% yield (Scheme A.3). The single crystal suitable for X-ray crystallography was obtained by diffusion of diethyl ether in dichloromethane. 98 Scheme A.1 Synthesis of trans-C [Ru(trpy)(phpy)(NH3)][OTf] (14) with two methods Cl NH3 OTf OTf N N N Ru N 1) H2O/NH3, 2 h reflux Ru N Ru N Method 1 N + N N N N N 2) NH4OTf 5 14 15 yield: 52% OTf Method 2 Cl Cl N NCMe N MeCN Step 1: Ru Ru + KOTf + NaOH + Ru Cl Cl 20 h, 50 oC MeCN NCMe NCMe 12 yield: 69% %69 N OTf OTf N Ru N 1) Methanol, 24 h reflux N N NCMe N N + N N Step 2: Ru 2) MeCN/Pentane 3:5 MeCN NCMe 3) Excess Ether NCMe 12 13 yield: 55% OTf NH3 OTf N OTf N N N 1) NH3 (excess), DCE Ru N Ru N Step 3: Ru N N + N N N N N 2) Ether 13 14 15 yield: 79% 99 Scheme A.2 Synthesis of {[RuIII(trpy)(phpy)]2(𝜇-O)}[OTf]2 (16) (OTf)2 NH3 OTf N N N N N Ru N DCM/ Exposed to the air O Ru N Ru N N N N N 14 16 yield: 60% Scheme A.3 Synthesis of trans-C [Ru(trpy)(phpy)(OTf)] (15) N OTf OTf N N Ru N DCM Ru N + MeCN N N N N N OTf OTf N N Ru N DCM/Ether Ru N + MeCN N N N N 13 15 yield: 60% A.3.2 Cyclic Voltammetry of trans-C [Ru(trpy)(phpy)(NH3)][PF6] (10) in DFB CV of 10 in DFB shows a catalytic plateau when it is added to ammonia solution; however, the peak current decreases over the number of scans (50 cycles), and the shape starts to deviate from the catalytic process (Figure A.1). This data shows the glassy carbon electrode became poisoned, and this may be caused by the deposition of species on the surface of the electrode. 100 For testing the deposition on the surface of the electrode, the glassy carbon electrode was removed from the solution, rinsed with dry THF, and then inserted into a cell containing a fresh THF solution of ammonia and 0.1 M TBAPF6. CV of ferrocene on the surface of a glassy carbon electrode before and after bubbling ammonia in DFB solution of the catalyst was taken in fresh THF and compared in Figure A.2. This figure shows the peak current of Fc decreases and the shape of the peak deviates from the reversible process after taking CV from a GC electrode used in a DFB solution of ammonia. uncatalyzed ammonia uncatalyzed ammonia ___ complex 10 in presence of ammonia (2 cycles) ___ complex 10 in presence of ammonia ___ complex 10 in presence of ammonia (20 cycles) Current Density (mA/cm 2) Current Density (mA/cm2) (50 cycles) 10 Potential (V vs Ferrocene) Potential (V vs Ferrocene) Figure A.1 Left: CV of uncatalyzed ammonia (red) and catalyzed ammonia with 10 (green, blue); Right: CV of uncatalyzed ammonia (black) and catalyzed ammonia with 10, 50 cycles (red); The CVs were taken in DFB, using TBAPF6 (0.1 M) as supporting electrolyte with a scan rate of 100 mV s−1; WE: glassy carbon, RE: Ag/AgNO3, and CE: Pt mesh 101 1.2 1.0 Current Density (mA/cm 2) 0.8 Fe 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 Potential (V vs. Ferrocene) Potential (V vs Ag/AgNO3) Figure A.2 Overlay the CV of Ferrocene (Fc) in THF before (black) and after (blue) bubbling ammonia in DFB solution of 10, TBAPF6 (0.1 M); scan rate of 100 mV s−1; WE: glassy carbon, RE: Ag/AgNO3, and CE: Pt mesh Also, the XPS spectrum was taken from the surface of the GC electrode after the rinse test. The XPS results confirm the adsorption of nitrogen and fluorine on the electrode surface, suggesting the potential formation of polyamine through the reaction between ammonia and 1,2- difluorobenzene (Figure A.3). C1s N1s O1s Si2p F1s O KLL Si2s Figure A.3 Left: XPS spectrum from the surface of glassy carbon electrode before and after taking CV of ammonia in DFB in presence of 10, Right: microscopic imaging of the surface of the GC electrode after taking CV of ammonia in DFB in the presence of 10 102 A.3.3 Concentration of Ammonia in 1,2-Dichloroethane (DCE) To calculate the concentration of saturated ammonia in 1,2-dichloroethane (DCE), a 5 mL sample of 1,2-dichloroethane was saturated with ammonia for 10 minutes. Subsequently, 0.05 mL of the solution was extracted for use in this experiment. 1 mL of CD3CN was added to the 50 microliters of solution. 1H NMR was taken in CD3CN. According to the 1H NMR, the integral of ammonia is 0.25 which is 12 times smaller than 3. Figure A.4 shows the calculation according to the 1H NMR signals. According to this calculation, the concentration of ammonia in DCE is 1.05 M, which is three times more than THF (0.34 M). The concentration of ammonia in DCE was also calculated through the mole fraction of ammonia in 1,2-dichloroethane reported in IUPAC.104 The same number was also retained from this calculation which agrees with what we got experimentally (Figure A.5). concentration_of_ammonia_in_1_2-dichloroethane_in_d-ACN_PROTON_01 DCE formula: C2H4Cl2 Density of DCE: 1.25 g/mL Molar mass of DCE: 98.96 g/mol 0.05 mL of DCE which saturated with ammonia was taken to measure the concentration of ammonia! m = d.v m = 1.25 (g/mL)* 0.05 (mL) m = 62.5 mg 62.5 ÷ 98.96 = 0.6315 mmol DCE 0.6315 ÷ 12 = 0.0526 mmol of NH3 0.0526 ÷ 0.05 = 1.05 M 4.00 0.25 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 -1 -2 f1 (ppm) Figure A.4 1H NMR of 0.05 mL DCE saturated with ammonia in CD3CN 103 ,1 !"#$ &'()*+", = ,1 + ,2 ,1 0.0797 = ,1 + 0.6315 n1= 0.0546 !!"# 0.0526 ÷ 0.05 = 1.09 M Figure A.5 Concentration of ammonia in DCE calculated through the mole fraction of ammonia in DCE reported by IUPAC 104 APPENDIX B: NMR, IR, UV-Vis SPECTRA 1. NMR Spectra 6 Cl 5 4 3 7 2 8 N N Ru 1 19 9 N N 18 10 11 12 17 16 13 15 14 Figure B.1 1H NMR spectrum of [Ru(trpy)(phpy)Cl] in DCM-d2 105 20 6 NH3 PF6 5 4 3 7 2 8 N N Ru 1 19 9 N N 18 10 11 12 17 16 13 15 14 20 6 NH3 PF6 5 4 3 7 2 8 N N Ru 1 19 9 N N 18 10 11 12 17 16 13 15 14 Figure B.2 1H NMR spectrum of [Ru(trpy)(phpy)(NH3)][PF6] in DCM-d2. Top: full spectrum, Bottom: magnified aromatic region 106 8 NH3 7 PF6 4 3 6 5 2 N N Ru 1 19 N 18 9 15 10 17 14 16 11 13 12 Figure B.3 13C NMR spectrum of [Ru(trpy)(phpy)(NH3)][PF6] in DCM-d2 NH3 H19 H12 H2O 20 6 NH3 5 4 3 B 7 2 N Ru N 8 1 c 19 9 N b a N 18 10 11 12 17 16 13 15 14 Figure B.4 1H NMR and 1D- NOESY overlay for [Ru(trpy)(phpy)(NH3)][PF6] in DCM-d2 107 Cl Cl Ru Ru Cl Cl Water DMSO water DMSO Figure B.5 1H NMR spectrum of [(ƞ6-C6H6)RuCl(µ-Cl)]2 in DMSO-d6 6 5 7 PF6 4 8 3 9 water 2 N N 1 Ru N N 12 10 N 11 Ether Ether Figure B.6 1H NMR spectrum of [Ru(phpy)(MeCN)4][PF6] in MeCN-d3 108 20 N 6 5 4 3 PF6 water 7 2 8 N N Ru 1 19 9 N N 18 10 11 12 17 16 13 15 14 Ether Ether Figure B.7 1H NMR spectrum of trans-C [Ru(trpy)(phpy)MeCN][PF6] in MeCN-d3 20 OTf 6 6 NH3 OTf 5 4 3 5 4 3 7 7 2 2 8 N N 8 N N Ru 1 Ru 1 19 19 9 N 9 N 18 18 10 11 10 11 N N 12 17 12 17 16 16 13 13 15 15 14 14 2a 14 15 3a Unbonded NH3 109 20 NH3 6 5 4 3 7 2 8 N N Ru 1 19 9 N N 18 10 11 12 17 16 13 15 14 According to the 1H NMR, in crude product there is 10% side product when it dissolved in DCM instantly! Figure B.8 Top: 1H NMR spectrum of 14 and 15 in DCM-d2; Bottom: the ratio of the peaks The ratio is lower NH3 OTf than H NMR; N OTf maybe T1 for F of Ru N N N N bound triflate lower Ru N N N than free OTf Figure B.9 19F NMR spectrum of trans-C [Ru(trpy)(phpy)NH3][OTf] in DCM-d2 @ -30 C (Top); and @ room temperature (Bottom) 110 6 5 7 OTf 4 8 3 9 2 N N 1 Ru N N 12 10 N 11 Figure B.10 1H NMR spectrum of trans-C [Ru(trpy)(MeCN)4][OTf] in DCM-d2 20 N 6 OTf 5 4 3 7 2 8 N N Ru 1 19 9 N N 18 10 11 12 17 16 13 15 14 Figure B.11 1H NMR spectrum of trans-C [Ru(trpy)(phpy)(MeCN)][OTf] in DCM-d2 111 OTf 6 5 4 3 7 2 8 N N Ru 1 19 9 N N 18 10 11 12 17 16 13 15 14 Figure B.12 1H NMR spectrum of trans-C [Ru(trpy)(phpy)(OTf)] in DCM-d2 F 20 F C F O S O O 8 PF6 7 4 3 6 5 2 N N Ru 1 19 N 18 9 15 10 17 14 16 11 13 12 Figure B.13 13C NMR spectrum of trans-C [Ru(trpy)(phpy)(OTf)] in DCM-d2 112 NMe2-ppy_PROTON_01 8.69 8.68 8.68 8.68 7.74 7.74 7.74 7.73 7.72 7.71 7.71 7.71 7.71 7.70 7.69 7.40 7.40 7.39 7.39 7.34 7.34 7.33 7.33 7.33 7.32 7.32 7.28 7.28 7.27 7.27 7.26 7.25 7.24 7.24 7.23 7.23 7.22 7.21 6.77 6.76 6.76 6.75 6.75 6.75 6.74 3 H (m) 4 2 7.23 9 5 F (m) H 2N 1 7.33 N A (dt) C (m) E (q) D (dtd) B (s) 8.68 7.72 7.40 6.76 3.76 8 6 G (m) 7 7.27 Ethyl acetate Ethyl acetate Ethyl acetate 1.00 2.04 0.97 0.97 2.54 0.98 1.00 1.52 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 f1 (ppm) Figure B.14 1H NMR spectrum of 2-(3-aminophenyl)pyridine in chloroform-d1 9 N 4 1 8 7 2 3 6 N 5 THF THF 1 Figure B.15 H NMR spectrum of N,N,N-trimethyl-3-(pyridin-2-yl)benzenaminium in chloroform-d1 113 9 N 4 1 8 7 2 3 6 N 5 Figure B.16 1H NMR spectrum of 2-(3-(dimethylamino)phenyl)pyridine in chloroform-d1 6 Cl 5 4 3 7 2 N Ru N 8 1 18 9 N N 17 10 11 12 16 15 13 14 N 19 water Figure B.17 1H NMR spectrum of [Ru(trpy)(NMe2-phpy)Cl] in DCM-d2 114 20 6 NH3 5 4 3 7 2 N Ru N 8 1 18 9 N N 17 10 11 12 16 15 13 14 N 19 Figure B.18 1H NMR spectrum of [Ru(trpy)(NMe2-phpy)NH3][PF6] in DCM-d2 NH3 PF6 N Ru N N N N Figure B.19 19F NMR spectrum of [Ru(trpy)(NMe2-phpy)NH3][PF6] in DCM-d2 115 13 12 (OTf)2 14 11 N N N 10 N Ru 9 Ru O water N N N 7 8 N 1 6 5 2 4 3 Figure B.20 1H NMR spectrum of {[RuIII(trpy)(phpy)]2(𝜇-O)}[OTf]2 in DCM-d2 (OTf)2 N N N N Ru O Ru N N N N Figure B.21 19F NMR spectrum of {[RuIII(trpy)(phpy)]2(𝜇-O)}[OTf]2 in DCM-d2 116 21 20 H 2N NH2 6 PF6 5 4 3 7 2 8 N N Ru 1 19 9 N N 18 10 11 12 17 16 13 15 14 Ether Ref, CD2Cl2 Ether Figure B.22 1H NMR spectrum of [Ru(trpy)(phpy)(N2H4)][PF6] in DCM-d2 22 21 23 20 O PF6 6 5 4 3 7 2 8 N N Ru 1 19 9 N N 18 10 11 12 17 16 13 15 14 Bonded THF water Bonded THF Figure B.23 1H NMR spectrum of [Ru(trpy)(phpy)(THF)][PF6] in THF-d8 117 PF6 O N Ru N N N Figure B.24 19F NMR spectrum of [Ru(trpy)(phpy)(THF)][PF6] in THF-d8 7 6 NH3 5 4 3 2 N RuIII N 8 1 N N 9 15 10 11 14 12 13 Figure B.25 1H NMR spectrum of [RuIII(trpy)(phpy)(NH3)][PF6]2 in MeCN-d3 118 2. IR Spectra NCMe PF6 N Ru N N CO Cl Figure B.26 IR spectroscopy of Cis-[Ru(trpy)(CO)(Cl)(NCMe)][PF6] UV-Vis Spectra 0.45 Cl 0.4 N Ru N 0.35 N N 0.3 Absorbance (a.u.) 0.25 0.2 0.15 0.1 0.05 0 380 430 480 530 580 630 680 730 780 Wavelenght (nm) Figure B.27 Electronic absorption spectrum of [Ru(trpy)(phpy)Cl] in DCM 119 6 NH3 PF6 5 N Ru N N N 4 Absorbance (a.u.) 3 2 1 0 200 300 400 500 600 700 800 Wavelenght (nm) Figure B.28 Electronic absorption spectrum of 10 (0.05 mM) in DCM 120 APPENDIX C: CRYSTALLOGRAPHIC DETAILS Compound Ru_NH CCDC 1958914 Formula C26H22F6N5PRu Dcalc./ g cm-3 1.664 m/mm-1 6.098 Formula Weight 650.52 Color red Shape block Size/mm3 0.27×0.15×0.13 T/K 173(2) Crystal System orthorhombic Space Group Pbca a/Å 11.1574(2) b/Å 15.0150(2) c/Å 30.9992(6) a/° 90 Experimental. Single red block-shaped crystals of b/° 90 Ru_NH were used as received. A suitable crystal g /° 90 0.27×0.15×0.13 mm3 was selected and mounted on a nylon V/Å3 5193.25(15) Z 8 loop with paratone oil on an Bruker APEX-II CCD Z' 1 diffractometer. The crystal was kept at a steady T = Wavelength/Å 1.541838 173(2) K during data collection. The structure was solved Radiation type CuKa with the ShelXT (Sheldrick, G.M. (2015). Acta Cryst. Qmin/° 2.851 A71, 3-8) structure solution program using the Intrinsic Qmax/° 72.143 Measured Refl. 22717 Phasing solution method and by using Olex2 (Dolomanov Independent 4999 et al., 2009) as the graphical interface. The model was Refl. refined with version 2018/3 of ShelXL (Sheldrick, Acta Reflections 2868 with I > 2(I) Cryst. A64 2008, 112-122) using Least Squares Rint 0.1484 minimization. Parameters 353 Restraints 0 Crystal Data. C26H22F6N5PRu, Mr = 650.52, Largest Peak 0.816 orthorhombic, Pbca (No. 61), a = 11.1574(2) Å, b = Deepest Hole -0.702 15.0150(2) Å, c = 30.9992(6) Å, a = b = g = 90°, V = GooF 1.002 wR2 (all data) 0.1577 5193.25(15) Å3, T = 173(2) K, Z = 8, Z' = 1, µ (CuKa) = wR2 0.1293 6.098, 22717 reflections measured, 4999 unique (Rint = R1 (all data) 0.1240 0.1484) which were used in all calculations. The final wR2 R1 0.0607 was 0.1577 (all data) and R1 was 0.0607 (I > 2(I)). Figure C.1 Crystal Data for trans-C [Ru(trpy)(phpy)(NH3)][PF6] 121 Compound MRS122A Formula C42.5H46ClF6N10O6.5Ru2 S2 CCDC 2141981 Dcalc./ g cm-3 1.513 m/mm-1 6.422 Formula Weight 1216.60 Color green Shape needle-shaped Size/mm3 0.63×0.12×0.09 T/K 100.00(10) Crystal System triclinic Space Group P-1 a/Å 8.60284(12) Experimental. Single green needle-shaped crystals b/Å 16.5297(3) c/Å 19.4311(2) of MRS122A used as received. A suitable crystal with a/° 84.2406(12) dimensions 0.63 × 0.12 × 0.09 mm3 was selected and b/° 82.1477(10) mounted on a nylon loop with paratone oil on a XtaLAB g/° 77.9793(13) Synergy, Dualflex, HyPix diffractometer. The crystal V/Å3 2669.84(7) Z 2 was kept at a steady T = 100.00(10) K during data Z' 1 collection. The structure was solved with the ShelXS Wavelength/Å 1.54184 (Sheldrick, 2008) solution program using direct methods Radiation type Cu Ka and by using Olex2 1.5 (Dolomanov et al., 2009) as the Qmin/° 2.302 Qmax/° 79.884 graphical interface. The model was refined with ShelXL Measured Refl's. 42453 2018/3 (Sheldrick, 2015) using full matrix least squares Indep't Refl's 11357 minimisation on F2. Refl's I≥2 s (I) 10172 Rint 0.0569 Crystal Data. C42.5H46ClF6N10O6.5Ru2S2, Mr = Parameters 597 Restraints 70 1216.60, triclinic, P-1 (No. 2), a = 8.60284(12) Å, b = Largest Peak 1.707 16.5297(3) Å, c = 19.4311(2) Å, a = 84.2406(12)°, b = Deepest Hole -1.350 82.1477(10)°, g = 77.9793(13)°, V = 2669.84(7) Å3, T = GooF 1.034 100.00(10) K, Z = 2, Z' = 1, m(Cu Ka) = 6.422, 42453 wR2 (all data) 0.2322 reflections measured, 11357 unique (Rint = 0.0569) wR2 0.2265 R1 (all data) 0.0848 which were used in all calculations. The final wR2 was R1 0.0802 0.2322 (all data) and R1 was 0.0802 (I ≥ 2 s (I)). Figure C.2 Crystal Data for [Ru(trpy)(MeCN)4][OTf] 122 Compound MRS122D Formula C58H44F6N10O6Ru2S2 CCDC 2143742 Dcalc./ g cm-3 1.675 m/mm-1 5.998 Formula Weight 1357.29 Color dark purple Shape plate-shaped Size/mm3 0.06×0.05×0.02 T/K 100(2) Crystal System monoclinic Flack Parameter -0.004(3) Hooft Parameter -0.004(3) Space Group P21 Experimental. Single dark purple plate-shaped a/Å 8.82157(9) crystals of MRS122D recrystallised from a mixture of b/Å 34.5245(3) c/Å 8.83933(7) acetonitrile by vapor diffusion of ether. A suitable crystal a /° 90 with dimensions 0.06 × 0.05 × 0.02 mm3 was selected and b /° 90.9159(8) mounted on a nylon loop with paratone oil on a XtaLAB g /° 90 Synergy, Dualflex, HyPix diffractometer. The crystal was V/Å3 2691.76(4) kept at a steady T = 100(2) K during data collection. The Z 2 Z' 1 structure was solved with the ShelXT (Sheldrick, 2015) Wavelength/Å 1.54184 solution program using dual methods and by using Olex2 Radiation type Cu Ka 1.5 (Dolomanov et al., 2009) as the graphical interface. Qmin/° 2.560 The model was refined with ShelXL 2018/3 (Sheldrick, Qmax/° 77.347 Measured Refl's. 29489 2015) using full matrix least squares minimization on F2. Indep't Refl's 10304 Refl's I≥2 s (I) 9825 Crystal Data. C58H44F6N10O6Ru2S2, Mr = 1357.29, Rint 0.0378 monoclinic, P21 (No. 4), a = 8.82157(9) Å, b = Parameters 759 34.5245(3) Å, c = 8.83933(7) Å, b = 90.9159(8)°, a = g = Restraints 1 90°, V = 2691.76(4) Å3, T = 100(2) K, Z = 2, Z' = 1, µ (Cu Largest Peak 0.401 Deepest Hole -0.577 Ka) = 5.998, 29489 reflections measured, 10304 unique GooF 1.010 (Rint = 0.0378) which were used in all calculations. The wR2 (all data) 0.0506 final wR2 was 0.0506 (all data) and R1 was 0.0228 (I ≥ 2 wR2 0.0502 s (I)). R1 (all data) 0.0243 R1 0.0228 Figure C.3 Crystal Data for trans-C [Ru(trpy)(phpy)(MeCN)][OTf] 123 Compound MRS122B Formula C28H21Cl2F3N4O3RuS CCDC 2143549 Dcalc./ g cm-3 1.739 m/mm-1 7.622 Formula Weight 722.52 Color dark purple Shape needle-shaped Size/mm3 0.24×0.03×0.01 T/K 100.00(10) Crystal System triclinic Space Group P-1 a/Å 8.7423(4) b/Å 12.2419(4) c/Å 13.4261(4) a /° 85.201(3) Experimental. Single dark purple needle-shaped b /° 74.596(3) crystals of MRS122B recrystallised from a DCM solution g /° 86.922(3) V/Å3 1379.67(9) by vapor diffusion of Ether. A suitable crystal with Z 2 dimensions 0.24 × 0.03 × 0.01 mm3 was selected and Z' 1 mounted on a nylon loop with paratone oil on a XtaLAB Wavelength/Å 1.54184 Synergy, Dualflex, HyPix diffractometer. The crystal was Radiation type Cu Ka kept at a steady T = 100.00(10) K during data collection. Qmin/° 3.423 Qmax/° 77.010 The structure was solved with the ShelXT (Sheldrick, Measured Refl's. 16113 2015) solution program using dual methods and by using Indep't Refl's 5504 Olex2 1.5 (Dolomanov et al., 2009) as the graphical Refl's I≥2 s (I) 5155 interface. The model was refined with ShelXL 2018/3 Rint 0.0514 (Sheldrick, 2015) using full matrix least squares Parameters 377 Restraints 3 minimization on F2. Largest Peak 1.249 Deepest Hole -1.478 Crystal Data. C28H21Cl2F3N4O3RuS, Mr = 722.52, GooF 1.065 triclinic, P-1 (No. 2), a = 8.7423(4) Å, b = 12.2419(4) Å, wR2 (all data) 0.1676 c = 13.4261(4) Å, a = 85.201(3)°, b = 74.596(3)°, g = wR2 0.1646 86.922(3)°, V = 1379.67(9) Å3, T = 100.00(10) K, Z = 2, R1 (all data) 0.0638 R1 0.0614 Z' = 1, µ (Cu Ka) = 7.622, 16113 reflections measured, 5504 unique (Rint = 0.0514) which were used in all calculations. The final wR2 was 0.1676 (all data) and R1 was 0.0614 (I ≥ 2 s (I)). Figure C.4 Crystal Data for trans-C [Ru(trpy)(phpy)(OTf)] 124 Compound MRS820F Formula C28H24ClN5Ru CCDC 2025826 Dcalc./ g cm-3 1.582 m/mm-1 6.577 Formula Weight 567.04 Colour red Shape block Size/mm3 0.27×0.14×0.02 T/K 100.00(10) Crystal System monoclinic Space Group P21/n a/Å 11.54823(12) b/Å 14.72974(16) c/Å 14.16952(16) a /° 90 b /° 99.0529(11) g /° 90 Experimental. Single red block crystals of MRS820F V/Å3 2380.24(5) recrystallised from a mixture of DCM and ether by Solvent Z 4 Z' 1 diffusion. A suitable crystal with dimensions 0.27 × Wavelength/Å 1.54184 0.14 × 0.02 mm3 was selected and mounted on a nylon Radiation type Cu Ka loop with paratone oil on a XtaLAB Synergy, Dualflex, Qmin/° 4.358 HyPix diffractometer. The crystal was kept at a steady T = Qmax/° 77.427 Measured Refl's. 17907 100.00(10) K during data collection. The structure was Indep't Refl's 4880 solved with the ShelXT (Sheldrick, 2015) solution Refl's I≥2 s (I) 4520 program using dual methods and by using Olex2 Rint 0.0513 (Dolomanov et al., 2009) as the graphical interface. The Parameters 318 model was refined with ShelXL 2018/3 (Sheldrick, 2015) Restraints 0 Largest Peak 0.826 using full matrix least squares minimisation on F2. Deepest Hole -1.010 GooF 1.071 Crystal Data. C28H24ClN5Ru, Mr = 567.04, wR2 (all data) 0.0948 monoclinic, P21/n (No. 14), a = 11.54823(12) Å, b = wR2 0.0922 14.72974(16) Å, c = 14.16952 (16) Å, b = 99.0529 (11)°, R1 (all data) 0.0369 R1 0.0346 a = g = 90°, V = 2380.24(5) Å3, T = 100.00 (10) K, Z = 4, Z' = 1, µ(Cu Ka) = 6.577, 17907 reflections measured, 4880 unique (Rint = 0.0513) which were used in all calculations. The final wR2 was 0.0948 (all data) and R1 was 0.0346 (I ≥ 2 s (I)). Figure C.5 Crystal Data for trans-C [Ru(trpy)(NMe2-phpy)(Cl)] 125 Compound MRS820G_twin1_h klf4 Formula C28H27F6N6PRu Dcalc./ g cm-3 1.639 m/mm-1 5.682 Formula Weight 693.59 Color red Shape block-shaped Size/mm3 0.10×0.06×0.04 T/K 100.01(10) Crystal System triclinic Space Group P-1 a/Å 11.7043(4) b/Å 15.2182(5) c/Å 15.7973(6) Experimental. Single red block-shaped crystals of a /° 91.689(3) MRS820G_twin1_hklf4 used as received. A suitable b /° 90.420(3) crystal with dimensions 0.10 × 0.06 × 0.04 mm3 was g /° 91.493(3) selected and mounted on a nylon loop with paratone oil V/Å3 2811.52(17) Z 4 on a XtaLAB Synergy, Dualflex, HyPix diffractometer. Z' 2 The crystal was kept at a steady T = 100.01(10) K during Wavelength/Å 1.54184 data collection. The structure was solved with the Radiation type Cu Ka ShelXT (Sheldrick, 2015) solution program using dual Qmin/° 2.906 methods and by using O. V. Dolomanov, L. J. Bourhis, Qmax/° 77.727 Measured Refl's. 24982 R. J. Gildea, J. A. K. Howard and H. Puschmann, Olex2: Indep't Refl's 24982 a complete structure solution, refinement, and analysis Refl's I≥2 s (I) 19708 program.J. Appl. Cryst. (2009). 42, 339-341. as the Rint . graphical interface. The model was refined with ShelXL Parameters 799 2018/3 (Sheldrick, 2015) using full matrix least squares Restraints 297 minimization on F2. Largest Peak 2.447 Deepest Hole -1.627 Crystal Data. C28H27F6N6PRu, Mr = 693.59, GooF 1.097 wR2 (all data) 0.2728 triclinic, P-1 (No. 2), a = 11.7043(4) Å, b = wR2 0.2615 15.2182(5) Å, c = 15.7973(6) Å, a = 91.689(3)°, b = R1 (all data) 0.1111 90.420(3)°, g = 91.493(3)°, V = 2811.52(17) Å3, T = R1 0.0914 100.01(10) K, Z = 4, Z' = 2, m(Cu Ka) = 5.682, 24982 reflections measured, 24982 unique which were used in all calculations. The final wR2 was 0.2728 (all data) and R1 was 0.0914 (I ≥ 2 s (I)). Figure C.6 Crystal Data for trans-C [Ru(trpy)(NMe2-phpy)(NH3)]PF6. The crystal of this compound was found to be twinned. Refinement of the twin component showed two twin orientations (0.35 and 0.28 percent) 126 Compound RuDMF Formula C19H18ClF6N4O2P Ru CCDC 1958364 Dcalc./ g cm-3 1.831 m/mm-1 0.969 Formula Weight 615.86 Colour orange Shape needle-shaped Size/mm3 0.47×0.10×0.07 T/K 173(2) Crystal System monoclinic Space Group P21/c a/Å 8.479(2) b/Å 11.693(3) c/Å 22.539(6) Experimental. Single orange needle-shaped crystals of a /° 90 RuDMF were used as received. A suitable crystal 0.47×0.10×0.07 b /° 91.010(4) mm3 was selected and mounted on a nylon loop with paratone oil g /° 90 V/Å3 2234.4(10) on a Bruker APEX-II CCD diffractometer. The crystal was kept at Z 4 a steady T = 173(2) K during data collection. The structure was Z' 1 solved with the ShelXT (Sheldrick, G.M. (2015). Acta Cryst. A71, Wavelength/Å 0.71073 3-8) structure solution program using the Intrinsic Phasing solution Radiation type MoKa Qmin/° 1.807 method and by using Olex2 (Dolomanov et al., 2009) as the Qmax/° 27.519 graphical interface. The model was refined with version 2018/3 of Measured Refl's. 20494 ShelXL (Sheldrick, Acta Cryst. A64 2008, 112-122) using Least Indep't Refl's 5092 Squares minimization. Refl's I≥2 s (I) 3545 Rint 0.0757 Crystal Data. C19H18ClF6N4O2PRu, Mr = 615.86, monoclinic, Parameters 309 Restraints 0 P21/c (No. 14), a = 8.479(2) Å, b = 11.693(3) Å, c = 22.539(6) Å, Largest Peak 0.824 b = 91.010(4)°, a = g = 90°, V = 2234.4(10) Å3, T = 173(2) K, Z = Deepest Hole -0.447 4, Z' = 1, µ (MoKa) = 0.969, 20494 reflections measured, 5092 GooF 0.991 unique (Rint = 0.0757) which were used in all calculations. The final wR2 (all data) 0.0973 wR2 0.0857 wR2 was 0.0973 (all data) and R1 was 0.0444 (I > 2(I)). R1 (all data) 0.0807 R1 0.0444 Figure C.7 Crystal Data for [Ru(trpy)(CO)(Cl)(DMF)][PF6] 127 Compound RU-purple CCDC 1959745 Formula C18H14ClF6N4OP Ru Dcalc./g cm-3 1.850 m/mm-1 1.023 Formula Weight 583.82 Color red Shape needle Size/mm3 0.22×0.10×0.07 T/K 173(2) Crystal System orthorhombic Flack Parameter 0.6(2) Hooft Parameter 0.57(8) Space Group Pca21 Experimental. Single red needle-shaped crystals of a/Å 17.716(7) RU-purple were used as received. A suitable crystal b/Å 7.452(3) 0.22×0.10×0.07 mm3 was selected and mounted on a nylon c/Å 15.880(6) loop with paratone oil on a Bruker APEX-II CCD a/° 90 b/° 90 diffractometer. The crystal was kept at a steady T = g/° 90 173(2) K during data collection. The structure was solved V/Å3 2096.5(14) with the ShelXT (Sheldrick, G.M. (2015). Acta Cryst. Z 4 A71, 3-8) structure solution program using the Direct Z' 1 Wavelength/Å 0.710730 Methods solution method and by using Olex2 (Dolomanov Radiation type MoKa et al., 2009) as the graphical interface. The model was Qmin/° 2.299 refined with version 2018/3 of ShelXL (Sheldrick, Acta Qmax/° 25.417 Cryst. A64 2008, 112-122) using Least Squares Measured Refl. 15790 Independent 3775 minimization. Refl. Reflections with 2237 Crystal Data. C18H14ClF6N4OPRu, Mr = 583.82, I > 2(I) orthorhombic, Pca21 (No. 29), a = 17.716(7) Å, b = Rint 0.0639 Parameters 430 7.452(3) Å, c = 15.880(6) Å, a = b = g = 90°, V = Restraints 540 Largest Peak 1.474 2096.5(14) Å3, T = 173(2) K, Z = 4, Z' = 1, µ (MoKa) = Deepest Hole -0.462 1.023, 15790 reflections measured, 3775 unique (Rint = GooF 1.036 wR2 (all data) 0.2101 0.0639) which were used in all calculations. The final wR2 wR2 0.1744 R1 (all data) 0.1093 was 0.2101 (all data) and R1 was 0.0668 (I > 2(I)). R1 0.0668 Figure C.8 Crystal Data for trans-[Ru(trpy)(CO)(Cl)(NCMe)][PF6] 128 Compound Ru_Yellow CCDC 1958381 Formula C18H14ClF6N4OPRu Dcalc./ g cm-3 1.916 m/mm-1 1.060 Formula Weight 583.82 Colour yellow Shape chunk Size/mm3 0.19×0.17×0.17 T/K 173(2) Crystal System triclinic Space Group P-1 a/Å 8.1466(7) b/Å 8.8170(8) c/Å 14.7557(13) a /° 102.1110(10) b/ ° 100.5940(10) Experimental. Single yellow chunk-shaped crystals of g/ ° 94.1550(10) Ru_Yellow were used as received. A suitable crystal V/Å3 1011.81(15) Z 2 0.19×0.17×0.17 mm3 was selected and mounted on a nylon Z' 1 loop with paratone oil on a Bruker APEX-II CCD Wavelength/Å 0.710730 diffractometer. The crystal was kept at a steady T = Radiation type MoKa 173(2) K during data collection. The structure was solved Qmin/° 1.442 with the ShelXT (Sheldrick, G.M. (2015). Acta Cryst. Qmax/° 25.407 Measured Refl. 16521 A71, 3-8) structure solution program using the Intrinsic Independent 3711 Phasing solution method and by using Olex2 (Dolomanov Refl. et al., 2009) as the graphical interface. The model was Reflections 3264 refined with version 2018/3 of ShelXL (Sheldrick, Acta with I > 2(I) Rint 0.0404 Cryst. A64 2008, 112-122) using Least Squares Parameters 290 minimization. Restraints 0 Largest Peak 0.683 Crystal Data. C18H14ClF6N4OPRu, Mr = 583.82, Deepest Hole -0.411 triclinic, P-1 (No. 2), a = 8.1466(7) Å, b = 8.8170(8) Å, GooF 1.097 wR2 (all data) 0.0838 c = 14.7557(13) Å, a = 102.1110(10)°, b = 100.5940(10)°, wR2 0.0792 g = 94.1550(10)°, V = 1011.81(15) Å3, T = 173(2) K, Z = 2, R1 (all data) 0.0388 Z' = 1, µ (MoKa) = 1.060, 16521 reflections measured, R1 0.0329 3711 unique (Rint = 0.0404) which were used in all calculations. The final wR2 was 0.0838 (all data) and R1 was 0.0329 (I > 2(I)). Figure C.9 Crystal Data for Cis-[Ru(trpy)(CO)(Cl)(NCMe)][PF6] 129 Compound MRS819A CCDC 1946952 Formula C53H40Cl2F18N8OP3R u2 Dcalc./g cm-3 1.791 m/mm-1 7.028 Formula Weight 1512.88 Color red Shape needle Size/mm3 0.16×0.12×0.06 T/K 173(2) Crystal System monoclinic Space Group P21/c a/Å 16.7648(4) b/Å 13.9819(4) c/Å 24.0323(7) Experimental. Single red needle-shaped crystals of a /° 90 MRS819A were used as received. A suitable crystal b /° 95.261(2) g /° 90 0.16×0.12×0.06 mm3 was selected and mounted on a nylon V/Å3 5609.5(3) loop with paratone oil on a Bruker APEX-II CCD Z 4 diffractometer. The crystal was kept at a steady T = Z' 1 173(2) K during data collection. The structure was solved Wavelength/Å 1.541838 Radiation type CuKa with the ShelXT (Sheldrick, G.M. (2015). Acta Cryst. Qmin/° 2.647 A71, 3-8) structure solution program using the Intrinsic Qmax/° 70.294 Phasing solution method and by using Olex2 (Dolomanov Measured Refl. 36835 et al., 2009) as the graphical interface. The model was Independent 10595 Refl. refined with version 2018/3 of ShelXL (Sheldrick, Acta Reflections 5712 Cryst. A64 2008, 112-122) using Least Squares with I > 2(I) minimization. Rint 0.2123 Parameters 784 Crystal Data. C53H40Cl2F18N8OP3Ru2, Mr = 1512.88, Restraints 0 Largest Peak 1.300 monoclinic, P21/c (No. 14), a = 16.7648(4) Å, b = Deepest Hole -0.598 13.9819(4) Å, c = 24.0323(7) Å, b = 95.261(2)°, a = g = GooF 0.972 90°, V = 5609.5(3) Å3, T = 173(2) K, Z = 4, Z' = 1, wR2 (all data) 0.1755 µ (CuKa) = 7.028, 36835 reflections measured, 10595 wR2 0.1392 R1 (all data) 0.1472 unique (Rint = 0.2123) which were used in all calculations. R1 0.0676 The final wR2 was 0.1755 (all data) and R1 was 0.0676 (I > 2(I)). Figure C.10 Crystal Data for {[RuIII/IV(trpy)(phpy)]2(𝜇-O)}[PF6]3 130 Compound MRS1221A Formula C27H19F3N4O3.5RuS CCDC 2129579 Dcalc./ g cm-3 1.659 m/mm-1 6.217 Formula Weight 645.59 Color red Shape needle-shaped Size/mm3 0.28×0.04×0.04 T/K 100.00(10) Crystal System orthorhombic Space Group Pnna a/Å 13.67281(14) Experimental. Single red needle-shaped crystals of b/Å 16.48864(15) MRS1221A used as received from NMR TUBE. A c/Å 22.9233(2) suitable crystal with dimensions 0.28 × 0.04 × 0.04 mm3 a/° 90 b/° 90 was selected and mounted on a nylon loop with paratone g/° 90 oil on a XtaLAB Synergy, Dualflex, HyPix V/Å3 5167.97(8) diffractometer. The crystal was kept at a steady T = Z 8 100.00(10) K during data collection. The structure was Z' 1 Wavelength/Å 1.54184 solved with the ShelXS (Sheldrick, 2008) solution Radiation type Cu Ka program using direct methods and by using Olex2 1.5 Qmin/° 3.302 (Dolomanov et al., 2009) as the graphical interface. The Qmax/° 79.716 model was refined with ShelXL 2018/3 (Sheldrick, Measured Refl's. 22698 Indep't Refl's 5548 2015) using full matrix least squares minimisation on F2. Refl's I≥2 s (I) 5074 Rint 0.0393 Crystal Data. C27H19F3N4O3.5RuS, Mr = 645.59, Parameters 357 orthorhombic, Pnna (No. 52), a = 13.67281(14) Å, b = Restraints 0 16.48864(15) Å, c = 22.9233(2) Å, a = b = g = 90°, V = Largest Peak 1.198 5167.97(8) Å3, T = 100.00(10) K, Z = 8, Z' = 1, m(Cu Deepest Hole -0.916 GooF 1.034 Ka) = 6.217, 22698 reflections measured, 5548 unique wR2 (all data) 0.1065 (Rint = 0.0393) which were used in all calculations. The wR2 0.1039 final wR2 was 0.1065 (all data) and R1 was 0.0373 (I≥2 R1 (all data) 0.0402 s(I)). R1 0.0373 Figure C.11 Crystal Data for {[RuIII(trpy)(phpy)]2(𝜇-O)}[OTf]2 131 Compound Ru_N2H4 CCDC 1962310 Formula C26H23F6N6PRu Dcalc./ g cm-3 1.525 m/mm-1 5.487 Formula Weight 665.54 Colour reddish green Shape plate Size/mm3 0.16×0.13×0.04 T/K 173(1) Crystal System triclinic Space Group P-1 a/Å 12.6633(2) b/Å 14.5339(3) c/Å 16.3726(3) Experimental. Single reddish green plate-shaped a /° 88.0730(10) b/° 77.4930(10) crystals of Ru_N2H4 were recrystallized from a mixture of g /° 80.1680(10) DCM and ether by solvent layering. A suitable crystal V/Å3 2898.60(9) 0.16×0.13×0.04 mm3 was selected and mounted on a nylon Z 4 loop with paratone oil on a Bruker APEX-II CCD Z' 2 Wavelength/Å 1.541838 diffractometer. The crystal was kept at a steady T = Radiation type CuKa 173(1) K during data collection. The structure was solved Qmin/° 2.76 with the ShelXT (Sheldrick, G.M. (2015). Acta Cryst. Qmax/° 72.11 A71, 3-8) structure solution program using the Intrinsic Measured Refl. 40285 Phasing solution method and by using Olex2 (Dolomanov Independent 10942 Refl. et al., 2009) as the graphical interface. The model was Reflections 9497 refined with version 2018/3 of ShelXL (Sheldrick, Acta with I > 2(I) Cryst. A64 2008, 112-122) using Least Squares Rint 0.0495 minimization. Parameters 773 Restraints 0 Largest Peak 0.680 Crystal Data. C26H23F6N6PRu, Mr = 665.54, triclinic, Deepest Hole -0.542 P-1 (No. 2), a = 12.6633(2) Å, b = 14.5339(3) Å, c = GooF 1.029 16.3726(3) Å, a = 88.0730(10)°, b = 77.4930(10)°, g = wR2 (all data) 0.0850 80.1680(10)°, V = 2898.60(9) Å3, T = 173(1) K, Z = 4, Z' = wR2 0.0816 R1 (all data) 0.0396 2, µ (CuKa) = 5.487, 40285 reflections measured, 10942 R1 0.0333 unique (Rint = 0.0495) which were used in all calculations. The final wR2 was 0.0850 (all data) and R1 was 0.0333 (I>2(I)). Figure C.12 Crystal Data for [Ru(trpy)(phpy)(N2H4)][PF6] 132 Compound MRS719C CCDC 1959276 Formula C34H35F6N4O2PRu Dcalc./ g cm-3 1.572 µ/mm-1 4.960 Formula Weight 777.70 Colour purple Shape needle Size/mm3 0.46×0.06×0.04 T/K 173(2) Crystal System triclinic Space Group P-1 a/Å 13.8078(6) b/Å 17.5333(8) c/Å 20.6228(9) a/° 88.370(3) Experimental. Single purple needle-shaped crystals of b /° 81.058(3) MRS719C were used as received. A suitable crystal g /° 88.949(3) 0.46×0.06×0.04 mm3 was selected and mounted on a nylon V/Å3 4929.5(4) loop with paratone oil on a Bruker APEX-II CCD Z 6 Z' 3 diffractometer. The crystal was kept at a steady T = Wavelength/Å 1.541838 173(2) K during data collection. The structure was solved Radiation type CuKa with the ShelXT (Sheldrick, G.M. (2015). Acta Cryst. Qmin/° 2.169 A71, 3-8) structure solution program using the Intrinsic Qmax/° 70.272 Phasing solution method and by using Olex2 (Dolomanov Measured Refl. 53381 Independent 17936 et al., 2009) as the graphical interface. The model was Refl. refined with version 2018/3 of ShelXL (Sheldrick, Acta Reflections 10655 Cryst. A64 2008, 112-122) using Least Squares with I > 2(I) minimization. Rint 0.1313 Parameters 1222 Restraints 0 Crystal Data. C34H35F6N4O2PRu, Mr = 777.70, Largest Peak 2.523 triclinic, P-1 (No. 2), a = 13.8078(6) Å, b = 17.5333(8) Å, Deepest Hole -1.146 c = 20.6228(9) Å, a = 88.370(3)°, b = 81.058(3)°, g = GooF 1.033 88.949(3)°, V = 4929.5(4) Å3, T = 173(2) K, Z = 6, Z' = 3, wR2 (all data) 0.2790 wR2 0.2375 µ (CuKa) = 4.960, 53381 reflections measured, 17936 R1 (all data) 0.1488 unique (Rint = 0.1313) which were used in all calculations. R1 0.0893 The final wR2 was 0.2790 (all data) and R1 was 0.0893 (I > 2(I)). Figure C.13 Crystal Data for [Ru(trpy)(phpy)(THF)][PF6] 133