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I: , ‘: IN. u. ,f .7 ' . wrn'g I)". ‘2- % f ‘ ' f9. 5%,}, . . - ‘3 w " .‘-" .1 ‘ r..l x'” 1. ,V ‘1‘ ‘Ja- 3-1:? WI?» "‘13 I~I"‘ @utazvcvngfim ‘- ‘ , - r- ”'E‘ ‘. ‘f"‘2l"‘l‘n.‘ II n ’I I L :flii' .' “1}:JCETH W1 ‘\.I '..' H “;‘..|:'1h".l,l :.|" \I IE III-3,). M #1 f" 36"...“ H in $12: W'y’fiarn ~I~ . .1...' LE!» 3..» * S This is to certify that the thesis entitled IZZE Off/{‘ZQ'fv‘ofl o¥.0. Cg‘giodt‘o Ll‘jwflj 7(‘0’ {AQ I” 1(¢MCQ(q,f,D" ‘91“ (OfCI/{icQ’// #CCICVL / r14“ {'0( (CP‘f/g X (5 ‘wt Swfi (/(Kj/ La7¢>V --Ca {[6, g c presented by 5'; {c C ,(‘C ; CL)C//c‘¢m flora/4% QUQ7/C has been accepted towards fulfillment of the requirements for [/7 p degreein CAGMU‘*"7 Major professor DaMéNZ/g my 0-7639 THE UTILIZATION OF A CATIONIC LIGAND FOR THE INTERCALATION OF CATALYTICALLY ACTIVE METAL COMPLEXES IN SHELLING. LAYER-LATTICE SILICATES By William Harold Quayle A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Chemistry 1978 ABSTRACT THE UTILIZATION OF A CATIONIC LIGAND FOR THE INTEHCALATION OF CATALYTICALLY ACTIVE METAL COMPLEXES IN SWELLING. LAYER-LATTICE SILICATES By William Harold Quayle The substitution of a positively charged phosphine ligand. (PhZPCHZCHZPPhZCHzPh)BF“. (P-?+BF4). for Ppr.3 in the preparation of a Wilkinson type complex. RhCle. has generated a cationic olefin hydrogenation catalyst. The catalyst employing a 1.1.1 ratio of P-§+BFu.PPh3.Rh(I) (A) is active for the hydrogenation of 1-hexene both in methanol solution and when exchanged within the intracrystal space of the mineral hectorite. flahcucomjz + P-P+BFu + PPhB + H2 —) A (Hectorite is a swelling. mica-like magnesio-silicate with cation exchange properties). Significantly. the activity or the mineral supported catalyst was about 1.9 times greater than the homogeneous catalyst. 31? nmr studies have indicated that the 1.1.1 catalyst (A) is a mixture of two or more cationic. mixed phosphine. rhodium(I) chloride complexes that generate highly active intermediates for olefin hydrogenation. These intermediates are probably analogous to those proposed1 for the uncharged HhCle system. Hectorite appears to increase the catalytic activity of the 1.1.1 system. This may be attributed to the solution-like environment within the support and the William Harold Quayle ability of the large negatively charged silicate sheets to alter the stoichiometry and geometry of the complexes involved. These results show that positively charged ligands may be employed to produce active cationic transition metal catalysts which are analogous to known. otherwise neutral, homogeneous catalysts and which are capable of electrostatic attachment to an anionic support. In particular. hectorite seems an ideal support for immobilization of such catalysts. Further implementation of this innovation should allow the simple. convenient preparation of a variety of cationic complexes and catalysts which would not be susceptible to desorption from anionic supports and which may also extend the range of solvent systems available to certain homogeneous catalysts. It was found that 2.0.1 and 3.0.1 ratios of P-P+BFus PPhBaRh(I) generated complexes which were capable of oxida- tively adding 32' but were inactive as olefin hydrogenation catalysts both in solution and when supported in the mineral environment. Similarly. Rh(I) and Rh(III) complexes bound to hectorite which had been exchanged with the cationic phosphine ligand (P-P+/Hect) also added hydrogen but were catalytically inactive. The inactivity of these systems for olefin hydrogenation was attributed to steric crowding at the rhodium center by the bulky positively charged ligand. which interferes with the dissociative and associative processes that must occur within the metal's coordination sphere in order for catalysis to occur. The cationic ligand William Harold Quayle does play an active role in the reactivity of the 1.1.1 catalyst, however since a 1.1 PPhasnh system is a very poor catalyst and loses activity very soon after initiation of the reaction. In addition. 31F nmr studies have shown that all of the cationic ligand is bound to the rhodium in the 1.1.1 system. The coordination of P-P+BF4 with the less bulky ligand, PPha, generates complexes which are not as sterically crowded, resulting in active catalytic species. A rhodium(I) complex containing the cationic ligand was isolated and characterized by ir. 1H'nmr and 31F nmr spectroscopy. It was found, as expected, that [RhCl(COD)- (P-P+L]BFu was spectroscopically similar to the analogous RhCl( con) (PPhB) complex. Contact of [RhCl(COE)2_]2 with hectorite, P-§+/Hect, kaolinite or silica gel. for 2h hours, resulted in the formation of supported Rh(0) materials. These materials were comparable in activity to commercial 5% Rh(0) on alumina for the hydrogenation of i-hexene and benzene. The Bh(0) formation was attributed to a surface catalyzed disproportionation reaction of [RhC1(COE)2]2 to Rh(0) and Rh(III) species. It was found that silylation of the surface hydroxyl groups of hectorite by a mixture of (Me381)2NH and heasiCl inhibited the disproportionation reaction. 1. C. A. Tolman. P. z. Meakin, D. L. Lindner. J. P. Jesson. J. Am, Chem. Soc.. 6, 2762 (197h). This work is dedicated to Laura with love. a good day today and a better day tomorrow. 11 ACKNOWLEDGMENTS I wish to thank Dr. Thomas J. Pinnavaia for his patient assistance in making my graduate school experience one which was academically fulfilling. spiritually uplifting and for the most part, eminently enjoyable. I am also most grateful for the editorial assistance given by my second reader. Dr. Bruce A. Averill. Special acknowledgement is due for the excellent faculty. the research and support staff. and the facilities at Michigan State University. . The early encouragement and advice provided by Dr. Arnold L. Rheingold. Dr. Gerald Kokoszka, Dr. Robert Ellsworth and Mr. John R. Maloney has been a continuing motivational force in these and other endeavors. The National Science Foundation and MSU furnished financial support for this study. 111 TABLE OF CONTENTS LIST OF TAEB O O O O O O O O 0 O O 0 LIST OF FIGURES . . . . . . . . . . . LIST OF SYMBOLS AND ABBREVIATIONS . . I. II. INTRODU“ I ON 0 O O O O O O O O O A. Foundation. Hemogeneous and Heterogeneous Catalysts . . Background. Supported Metal Complex Catalysts . . . . . The Use of Hectorite as a Catalyst Support. . . . . . Rationale. the Use of Cationic Ligands in Metal Complex Catalysts. EXPERIMENTAL. . . . . . . . . . A. B. Solvents and Reagents . . . Physical Methods. . . . . . 1. Infrared Spectra. . . . 2. Proton NMB Studies. . . 3. Phosphorus-31 NMB Studies h. X-ray Diffraction Study . 5. Elemental Analysis and Melting Points. . . . . . . . . iv Page vii viii 13 17 21 21 22 22 23 23 25 25 C. syntheses O O O O O O O O O O O O O O l. 2. 7. Known Rhodium Complexes . . . . . 1-Dipheny1phosphino-Z-benzyl- diphenylphosphoniumethane bromide Tetrafluoroborate Anion Exchange Resin . . . . . . . . . . . . . . 1-Diphenylphosphino-Z-benzyl- diphenylphosphoniumethane- tetrafluoroborate . . . . . . . . Chloro(1.5-cyclooctadiene) (1- diphenylphosphino-Z-benzyl- phenylphosphoniumethane) rhodium(I) tetrafluoroborate. . . 1-Diphenylphosphino-Z-benzyl- diphenylphosphoniumethane Exchanged Hectorite . . . . . . . Silylated Montmorillonite . . . . Hydrogenation Studies and Catalyst H eparat 1 on O O O O O O O O O O O O O 1. Hydrogenation Procedure and Apparatus . . . . . . . . . . . . Homogeneous Catalysts . . . . . . Heterogeneous Catalysts and ”at erials O O O O O O O O O O O O Page 25 25 27 28 28 29 29 30 30 3O 33 3h Page III. RESULTS AND DISCUSSION. . . . . . . . . . . no A. Preparation and Characterization of P-PIBFL, and [RhCl(COD)(P-P+)]BFu. . . . to B. Heterogeneous Systems I . . . . . . . . 52 1. RhCl(PPh3)3/Hect. RhClB/Hect, P-P+/Hect, RhCl(PPh3)3/P-P*/Hect. RhClB/P-P+/Hect and [thl(CoE)2]§/P-P*/Hect . . . . . . 52 2. Rh(O)/P-P+/Hect. Rh(0)/Hect. Rh(O)/Kaol and Rh(O)/SILG . . . . . 5n 3. RBSi/Mont and [thl(Cos)2]§/ R3Si/Mont . . . . . . . . . . . . . 56 C. Homogeneous Systems . . . . . . . . . . 58 1. Hydrogenations Employing 0.x.1 P-P+BPQ.PPh .ah Catalysts . . . . . 59 2. HydrogenatiZns Employing Y3X11 P-P+BFu.PPh3:Rh Catalysts . . . . . 61 3. Characterization of Catalyst Precursors. . . . . . . . . . . . . 66 D. Heterogeneous Systems II. Hydrogenations Employing iaiai/Hect, 0.2.1/Hect. Rh(COD)(PPh3)2+/Hect. 2:0:1/Hect and 3:0:1/Heot . . . . . . . 91 IV. CONCLUSIONS AND RECOMMENDATIONS . . . . . . 97 BIBLIOGRAPHI................... 10!. vi Table 1. 2. LIST OF TABLES Materials Used to Support Metal Complexes . Methods for Binding Metal Complex Catalysts to Supports . . . . . . . . . . . . . . . . Relevant 180 MHz Proton NMR Data for P-P+BFh and [thl(CoD)(P-P*)]Bru. . . . . . Initial Hydrogenation TO#'s for Supported Rh(0) Catalysts . . . . . . . . . . . . . . TO#'s for 0.x.1 Hydrogenation Catalysts . . TO#'s for Y1X31 Hydrogenation Catalysts . . TO#'s for lalsl/Reot. 1:111. 0:211 and Rh(coD)(PPh3)2+ Hydrogenation Catalysts. MINTO#'s for 0.2.1/Hect and Rh(COD)(PPh3)2+/ Hect Hydrogenation Catalysts. . . . . . . . Some Known Homogeneous Catalysts Potentially Suitable for Modification by Positively Charged Ligands . . . . . . . . . . . . . . vii Page 5? 6O 62 92 102 Figure 1. LIST OF FIGURES Schematic representation of hectorite structure . . . . . . . . . . . . . . . . . Hydrogenation apparatus (schematic) . . . . Infrared spectra of P-P+BF4 (A) and [thltC0D)(P-P*)]3Fu (B) as nuJol mulls between 031 salt plates. Insets were taken as fluorolube mulls. . . . . . . . . 36.u3 MHz 31? nmr'spectra of P-P+BPh (A). [RhCl(COD)(P-P+)JBFu (B) and RhCl(COD)(PPh3) (c) at 28° 1h CHZClZ. . . Temperature dependent 31anr spectra of [RhCl(COD)(P-P+)]3Fu. 0.1 g in CHZClz. The -80° spectrum was obtained at twice the instrument gain of the others. . . . . . . 31 Temperature dependent P nmr spectra of RhC1(COD)(PPh3) + PPhB. t 31 0.03 M in CH2C12 . Temperature dependen P nmr spectra of RhCl(COD)(PPh3) + PPh3 + tz. 0.03 M in CHzclz O O O O O O O O O O O O O O O O 0 viii Page 11. 32 #2 #6 51 69 7t. Figure Page 8. 10. 11. 12. Temperature dependent 31P nmr spectra of RhCl(C0D)(PPh3) + PPh3 + tz + y(1-hexene) 0.03 g_1n CHZClz. The +30°. -u2° and -61° spectra were taken at twice the instrument gain of the +1° and -21° spectra. . . . . . 77 t 31 Temperature dependen P nmr spectra of [ahCl(C0D)(P-P*)]Bpu + PPh 0.03 M'in agm1.. ... .. ... ?. ... .. .. 81 Temperature dependent 31POnmr spectra of [RhCl(COD)(P-P*)]BFh + PPh3 + H2. 0.03 g in CH2C12. . . . . . . . . . . . . . . . . at 31P nmr spectra of CH2C12 solutions containing: A. é[RhCl(COE)2]é + PPh B. £[RhCl(COE)2]é + 2PPh33 and C. §[RhCl(COE)2]é + 3PPh3. A and B. +28°. C. -Buoo e e e o e o o c e e o e o e o e e 87 38 31? nmr spectrum of [thl(COE)(P-P*)]2(3Fu)2 at +28°. 0.05 g in CHZClz. . . . . . . . . 9o 11 8086 BBP BFn-/R$8 in Bu COD COE CP ddt diphos dip! dt esr Et Me MINTO# LIST OF SYMBOLS AND ABBREVIATIONS acetylacetonate benzylbutylphthalate tetrafluoroborate anion exchange resin butyl 1.5-cyclooctadiene cyclooctene cyclopentadienyl catalyst turnover doublet doublet of doublets of triplets bis(1.2-diphenylphosphino)ethane 2,2'-dipyridyl doublet of triplets electron spin resonance ethyl ligand (usually phosphine) cationic ligand multiplet metal methyl minimum turnover number F" Ph P-P‘+ P-P+BFu P—P+Br ‘ P-P+/Hect py £3:s.§k¥t§""“’33’3+' RBSi/Mont 3 s s1)-0‘. 31)-o- TMS TO# x X/Hect. X/P-P+/Hect. X/RBSi/Mont. X/Y-Zeolite norbornadiene nuclear magnetic resonance phosphorus nucleus (usually in a phosphine) phosphonium phosphorus nucleus phenyl group 1-diphenylphosphino-Z-benzyl- diphenylphosphoniumethane P-P+ tetrafluoroborate P-P+ bromide P-P+ exchanged form of hectorite pyridine polymer supported functional STOHPS silylated montmorillonite singlet usually solvent molecule silica hydroxyl group functionality tetramethylsilane turnover number usually halogen or - as below - unknown material designations for materials and/ or catalyst: supported on hec- torite. P-P /Hect, kaolinite. silica gel. R Si/Mont or Y-Zeolite - rgspectively xi 1:111. 0:211. etc. )- Pth. )- PR2 designations for homogeneous catal sts generated in situ from.thC1(CODL]2. P-P*BF41 PPhasRh phosphine functional groups on supports. usually silica or polymer xii INTRODUCTION A. FoundationI Homogeneous and Heterogeneous Catalysts During the past two decades transition metal catalysts in homogeneous solution have found more and more application in the promotion of industrially important chemical processes. Examples of the larger scale processes are the hydroformyl- ation of propylene to butyraldehyde over cobalt carbonyl complexes (oxo process).1 the aqueous oxidation of ethylene to aoetaldehyde with palladium salts (Wacker process),2'3 the hydration of acetylene to aoetaldehyde with mercury and iron salts.2 the production of vinylz’n and substituteds vinyl acetates from olefins and acetic acid over palladium salts. the production of phenol by the oxidation of toluene over cobalt and copper salts (Dow toluene-benzoic acid process),2 and the production of acetic acid from methanol and carbon monoxide with rhodium complexes (Monsanto process).6 Concurrent advances in the field of transition metal organo- metallic chemistry have had a synergistic effect on the rapid development and mechanistic understanding of these systems.7 Theoretically. catalysis by discrete. soluble, transition metal complexes offers a number of distinct advantages over traditional heterogeneous transition metal catalysis. where 2 reactions occur at solid-gas or solid-liquid interfaces. Each metal complex is available for reaction in a homogen- eous system. whereas metal centers below the active surface sites in heterogeneous catalysts are not accessible. This results in greater overall catalytic efficiency and allows easier interpretation of kinetics studies in homogeneous systems. Despite the progress which has been made in the area of surface analysis in recent years.8 detailed understanding of chemisorption-catalysis mechanisms is generally impracticable in heterogeneous systems because the surface structure is too easily altered by slight changes in catalyst preparation. pretreatment and reaction conditions. In contrast, homogen- eous catalysts are readily characterized by powerful solution analysis and spectroscopic techniques. As a consequence. they are much easier to control with respect to specificity for substrates. product selection and reproducibility from batch to batch. Control of the electronic and steric require- ments of a given metal center for a particular reaction can be modified through judicious choice of ligand and/or solvent system. Hemogeneous catalysts suffer from three major practical problems. however. which are sufficient to preclude their use in most industrially important processes. First. unlike heterogeneous systems. separation of the homogeneous catalyst from the products at the end of the reaction is a major difficulty. Distillation is often inefficient. resulting in 3 loss of catalyst and/or product contamination. It may also destroy thermally unstable catalysts and/or leave behind high-boiling reaction byproducts. Extraction of the catalyst or products with other solvents is beset with similar problems. Even if the separation can be made sufficiently efficient. the cost of the resulting process may often be prohibitive. Second. homogeneous catalysts. particularly organomet- allic complexes. exhibit poor thermal stability compared to heterogeneous catalysts. Although reactions are often catal- yzed efficiently under mild conditions. a desired increase in the reaction rate as a result of increased temperature is often limited in these systems. Third. the term ”soluble” catalyst is almost a misnomer for many complexes since they are often only slightly soluble. and most are soluble or active in only a limited range of solvents. This feature often limits the number of possible substrates for a given catalyst system. Heterogeneous catalysts are not so restricted by solvent considerations. B. BapkgpoundI Supported Metal Complex Catalysts A.number of review papers have highlighted the efforts of a growing authorship attempting to combine the attractive virtues of homogeneous catalysts with the practical engineer- ing aspects of heterogeneous catalysts.9 The basic approach in this area has been to devise methods by which the more efficient. selective. homogeneous catalysts may be separated readily from the reactants/products. Efficient catalyst- product separation has been achieved in homogeneous systems h using: (1) complexes thermally stabilized in molten ligand 10 solvents. (ii) separation of catalysts from products in biphasic solvent systems:11 (iii) separation of products 12.13 through selective. permeable membranes: or (iv) catalysts bound to soluble. high molecular weight polymers.13 However. the supereminent method in this approach has been the attachment of otherwise homogeneous transition metal catalysts to a variety of insoluble supports. In general. this method offers the ease of separation. thermal stability. reactant/product phase flexibility. and develop- ment of efficient flow and/or batch processes usually associated with heterogeneous catalysts. Moreover. these systems usually allow a greater degree of reaction control. specificity. reproducibility and efficiency associated with their homogeneous counterparts. In certain cases the support even enhances the activity and/or specificity of the catalyst by reducing the number of unwanted side reactions1 and/or preferentially selecting certain reagents over others based on molecular size restrictionsls or dipolar effects.16 Hartley's list of materials which have been used to support metal complex catalysts9h is reproduced in Table 1. Of course. the choice of a particular support depends very much on the gross properties of the catalyst system and the desired effect of the supported catalyst on the specificity of the reaction. In general. inorganic materials have better mechanical and thermal stabilities under most reaction conditions than organic supports. However. organic polymers Table 1. Materials Used to Support Metal Complexes’ Inorganic Silica Zeolites Glass Clay Metal Oxides (alumina. etc.) Organic Polystyrene Polyamines Polyvinyls Polyallyls Polybutadiene Polyamino acids Urethanes Acrylic polymers Cellulose Cross-linked dextrans Agarose *taken from F. R. Hartley. P. N. Vezey. Advana Organometal. Chem.. 12. 189 (1977). 6 offer a wider range of surface flexibility. pore size. surface area. and polar group functionalization than the usual inorganic supports (silica. glass. metal oxides). A partial list of the variety of methods which have been used to support catalysts is provided in Table 2. Many of these result in supported metal catalysts which have no counterparts in homogeneous solution. These are particularly interesting systems because each catalyst site has a molecularity identical to that of its neighbors. These catalysts therefore offer greater site specificity. uniform- ity and reproducibility than traditional heterogeneous catalysts. HCwever. detailed elucidation of the chemical mechanisms governing their activity is difficult to achieve because analogies to well understood homogeneous systems are not easily made. Immobilization of complexes whose catalytic activity in solution is reasonably well understood mechanistically generally allows the interpretation and subsequent control of the resulting heterogeneous systems' reactivity. based on principles of organometallic chemistry as well as knowledge of the properties of the support. This has been amply demonstrated by Grubbs. Kroll and Sweet for polymer attached Wilkinson's catalyst.313'33° The activity of the homogeneous catalyst (RhCle) was retained when it was attached by covalent linkage to phosphinated polystyrene. The selectivity differences.observed between the supported and solution catalysts were rationalized in terms of effects 7 Table 2. Methods for Binding Metal Complex Catalysts to Supports Selected Methodsl with Examples f References 1. P sisor tion and ion-exc e a. inorganic support + RhCl(CO)(PPh3)/BBP.-€> supported liquid-phase catalysts 17 - 2+ b. 215)- so3 + [PMNHBMJ -) P)— 303' + ah2(onc)4-x"" + Pph3 —) [Rh(PPh3)n][P)- 303] 19 2- c. 2P)-N(CH3)3+ + [meld -> [P)-N(CH3)3]2[PdClu] 20 d. Na+/Hect + ha(OAc)u_xx+ + Pm.3 —) Rh(PPh3)fi+/Hect 21 e. Na+/I-Zeolite + C02+ + NH3 + NO -€> [Co(NH3)nNO]2+/Y-Zeolite 22 NaI/I-Zeolite + Rh(NH3)63+ + C0 + 32 —> th(CO)y/Y-Zeolite 23 Table 2. .2. (cont'd). Supported functional gpoup reactions (excludipg phosphines) b. so. s1)—03 4- Mg! -> 31)- 01mm1 + RH 31)-03+ 81)-0~ + s1)-0r1 MB“ '2 31)- 0,113,” 233 (a =- alkyl. allyl or aryl) Si)-OH + hxn —-) :3.i)-0Mxn._1 4» ex s1)—03 + [xalsltcszkrphzjmn -> [31)- osl1(CH2),PPh2]th + RX (x a C2350 . Cl') P)-Y + 10(an -) (P)- rmxwfim. (I s -C023. —OH. -C5HuN. -CHZCN. -NR2. ~SR. 'cazcsfih' -(CH2)XNR2) s1)- os:1(CHZ)xr + Midis.“ _) [Si)-08:1(CH2)XY]MXD.RE. (I 3 -CN. -N32. -05HuN, -CSHu’ -CR( COCR ~83) 3)? P)- 061153:- + N1(1=Ph3).. —9 [m— Césm1(PPh3)ZBr + 2mm3 9f 24 25 26 27 26b. 28 29 Table 2. (cont'd). 3. Reactions with phosphinated suppprts a. Direct reaction of metal halides with support )- Pth + 10% —) )- PPhZMXn $30.28a. b. Displacement of a ligand from the metal complex )-PPh2 + RhCl(PPh3)3 —) [)- PPhZJRhCl(PPh3)2 + PPh3 15. 31 )-Pth + Rh(acac)(CO)2 —) [)- Pph2]ah(aoac)(co) + co 26b. 30 2)-Pa2 + Rh(acac)(NBD) + 3* --> [>- PRZJZRMNBDY" + acaoH 32 )- Pph2 + Pd(PPh3)p -> [>- PPhZJPd(PPh3)3 + 1=1=h3 303 2)-PPh2 + §[RhCl(COE)2]z -> (1' )- PPhEJZRhClh! + 2001: 16, 33 c. Cleavage of p—chloro dirhodium complexes 2)-PPh2 + [RhCl(COD)]2 —> 2[)- Pphgshcucon) 26a.27f. Babocojn 31+ 2)-PPh2 + [RhCI(CO)z]2 -> 2[)- PP1'12,]RhC1(CO)2 26a.27d.h 10 imposed by the polymer/solvent system. The method most studied for complex attachment has been the covalent binding of transition metal complexes to supports pig functional group ligands. although physisorption and ion- exchange methods were among the first to be studied in this area.9h Physisorption is a particularly easy means of immobil- ization. but catalysts immobilized in this fashion suffer from the relative ease with which complexes desorb under most reaction conditions. Covalently and electrostatically bound complexes desorb much less readily. although the former may be leached from the support in the presence of excess free ligand or under conditions where the surface link is chemically degraded. Electrostatically bound complexes may desorb if electrolytes that compete for surface exchange sites are generated during the reaction. or if changes in oxidation state result in neutral or oppositely charged species. Surface bound complexes often lose the number of vibrational. rotational and translational degrees of freedom associated with their solution chemistry. This generally results in loss of activity in the bound versus solution environment. especially for covalently bound complexes with short chain length linkages where surface steric effects are very strong. Optimum conditions for maximum catalytic activity would be those under which the translational motion of the complex is restricted. to prevent catalyst dimerization/ polymerization and help maintain coordinative unsaturation at the metal center. while the vibrational and rotational 11 degrees of freedom of the complex are maintained. A covalent surface-complex link will always impose restrictions on the latter two types of molecular motion. whereas electro- statically bound ions may exist in very solution-like environments (in appropriate solvents) even when Closely associated with the support. Ion-exchange then appears to be an attractive method for catalyst support: unfortunately. the vast majority of soluble catalysts are neutral species. incapable of electrostatic binding to suitable materials. Pinnavaia. and coworkers. have demonstrated recently that cationic metal complex catalysts can be intercalated between the negatively charged sheets of swelling. mica- like layered silicates.21 For example. the complex Rh(PPh3)x+ was shown to be an active catalyst for the hydrogenation of alkenes and alkynes in the intracrystal space of the clay mineral hectorite. under mild conditions. The supported catalyst exhibited much larger specificity for hydrogenation of terminal olefins versus internal olefins in methanol than did the solution catalyst.19 The activity of Rh(PPh3)x+/Rect was about ten times less than the homogeneous catalyst for the hydrogenation of 1-hexene. while the activity of this catalyst supported on a cation exchange resin was approximately forty times less.19b In contrast. the activity of Rh(PPh3)i+/Hect for reduction of 1-hexyne was comparable to that of the solution catalyst. .One might infer from these results that although the catalyst behaves as it would in solution for reduction of 1-hexyne. 12 selective steric and adsorptive effects imposed by the support alter the reactivity for i-hexene hydrogenation. In addition. although direct comparison may not be legitimate- due to differences in reaction conditions. the greater catalytic activity in the crystalline mineral relative to the amorphous polymer might be attributed to the complexes' greater uniform distribution and availability in the intracrystal environment. These preliminary studies on catalysts electrostatically bound in the solvent swollen intracrystal space of layer- lattice silicates have illustrated the attractiveness of the approach. The method of support is relatively easy compared with other systems. The catalysts exhibit solution-like behavior and desirable. potentially controllable. selectivity effects when exchanged on these cheap. ubiquitous minerals. (Other properties of these supports are described in Section I. C.) It has been found. however. that certain of these systems possess undesirable properties. Desorption of catalytically active. presumably uncharged species occurs during reactions when [Rh(COD) (PPh3)2]+ . a known homogeneous 35 hydrogenation catalyst. exchanged onto these minerals is 36 employed as a hydrogenation or hydroformylation catalyst. 37 In addition. the lack of numerous. well studied. cationic homogeneous catalysts limits the range and type of complexes which could be supported. The intent of this dissertation was to investigate the possibility that positively charged ligands might be employed 13 to produce active cationic transition metal catalysts analogous to well known. otherwise neutral. homogeneous catalysts and capable of electrostatic attachment to anionic supports. This innovation should allow simple. convenient preparation of a variety of new cationic catalysts which would not be susceptible to desorption from anionic supports as a result of changes in metal oxidation state. C. The Use of Hectorite as a Catalyst Support Hectorite is a member of the class of naturally occurring clay minerals known as smeetites. This mineral's attractiveness as a catalyst support is directly related to the unique properties of the crystalline. two dimensional structure characteristic of smeetites.38 As illustrated schematically in Figure 1. it is composed of alternating arrays of exchangeable cations and negatively charged silicate layers. The silicate layer of hectorite consists of an octahedral magnesia (brucite) sheet which shares oxygen atoms with two parallel tetrahedral silica sheets on either side of it. The thickness of this layer is about 9.6 2. In the tetrahedral sheets. three of the four oxygen atoms of each tetrahedron are shared by three neighboring tetrahedra. The fourth oxygen atom is shared with the brucite sheet. This results in roughly hexagonal holes in the tetrahedral sheets formed by rings of six oxygen atoms. Hydroxyl groups replace oxygen atoms located within these (holes in the brucite sheet where intersheet sharing does not occur a 1h Si licote Loyer0 9.6 A V / «4; 3%? ‘. o=02- O=OH' or F“ Si4+ fills tetrahedral sites 4. Mg2 and Li... fill octahedral sites (Adapted from reference 38a) Figure 1. Schematic representation of hectorite structure V 15 Isomorphous substitution of lithium cations for magnesium cations in the brucite sheet results in negatively charged silicate layers. This charge is compensated for by an array of hydrated sodium ions located between these layers. This interlayer space can be swelled considerably by“a large number of solvents. particularly polar solvents such as water. alcohols and ketones. As a consequence. the sodium ions may be readily replaced by a variety of other cations and cationic complexes by simple ion-exchange methods. In sufficiently swollen smeetite systems the interlayer cations exist in solution-like environments. Hydrated Cu2+ and Mn2+ ions exhibit rapid. solution-like molecular tumbling on the esr time scale.39 as do protonated amine functional- ized nitroxide spin probes.“o Of the low molecular weight alcohol and water systems studied. these latter cations were most mobile in methanol swollen interlayers of hectorite. Cationic organometallic catalysts exhibiting solution-like mobility in hectorite interlayers should not lose appreciable activity compared to their homogeneous counterparts as a result of increased catalyst-substrate collision lifetimes. In addition. these solvated interlayer ions should be readily susceptible to attack by reagent molecules from bulk solution. The 755 mz/g surface area of the hectorite used in this study compares favorably with those of'otheerupport materials. (The surface area is computed from the unit cell weight and dimensions. 769 g/mol and 5.25 x 9.18 A respectively. without inclusion of the additional area that 16 may be attributed to crystal edges. 2-35). For example. the surface area of a commonly used organic polymer. Amberlite O XAD-2. is 120 mz/g.3 J The various types of silica used have varied from 200u1 or 3’4017b to 500 mz/g.26b Hectorite's large surface area. combined with its relatively low cation exchange capacity (CEO). 73 meq/ioo g. provides monovalent interlayer cations with a large interlayer area of 86 Xz/ion. Commercially available cation exchange resins offer no more than 16 xz/ion. Zeolites are restricted to cationic complexes of small size. Complexes containing triphenylphosphine ligands would be much too large to exchange into Y-type zeolites.22° Smectites have been known for many years as effective heterogeneous catalysts for a number of reactions. Theng has reviewed their use in the petroleum industry as cracking and polymerization catalysts.380 The active sites are of the Brbnsted and Lewis acid type. Synthetic smectites incorp- orating Ni(II) in the brucite sheet may be used as light petroleum hydrogenation catalysts. as well as Fisher-Tropsch process catalysts.“2 The nickel increases the surface acidity and hence. activity of these catalysts. which are also active for hydroisomerization and oligomerization of light hydrocarbon fractions.“3 The interlayer regions of smectites often alter the reactivities and stabilities of transition metal complexes. 2+ For example. Cu -arene complexes. not found in homogeneous l4. solution. are found and stabilized in smeetites. 4 The 1? thermodynamic stability constants of Ni2+. Zn2+ and Cd2+ ethylenediamine complexes in smeetite interlayers are at least 100 times greater than those of the solution complexes.u5 As mentioned in Section I. B. the intracrystal environment enhances the selectivity of certain catalytic reactions as well.21 In this regard it is interesting to note that brucite interlayers play an important role in the reduction of NZ to Mafia over‘V(OH)2 doped Mg(OH)2.)+6 The intracrystal environ- ment allows relatively unstable "232' the initial reduction product. to accumulate in sufficient local concentration to effect disproportionation to N2 and Nth. without appreciable decomposition to the elements. The ability of interlayer environments to play active. often constructive roles in transition metal complex chemistry and catalysis is one of the many reasons why clay minerals such as hectorite are being investigated as attractive homogeneous catalyst supports. D. Rationale. the Use of Cationic Ligands in Metal Complex Catalysts A catalyst system was chosen for this study to test the utilization of cationic ligands in otherwise neutral homo- geneous catalysts. Wilkinson's olefin hydrogenation catalyst. RhCl(PPh ) . has been studied relatively well. both in 3 x h? homogeneous solution and in supported environments (Table 2). The complex does not dissociate chloride to any observable extent in most solvent systems. It was felt that substitution of a cationic ligand for PPh in this catalyst would afford 3 a cationic complex with the neutral compound's characteristics. 18 which would be capable of electrostatic attachment to anionic supports like hectorite. The homogeneous catalyst may be generated pp.p;pp by the addition of an appropriate number of moles of PPh3 to [sh01(czsu)2]z.u7° [nnc1(cos)2]2“7f or [m.c1(c01>)]2.“8 followed by addition of Hz to generate the catalytically active dihydride. Alternatively. the desired amount of the solid compound. RhCl(PPh3)3. may be added directly to the solution.“78 followed by addition of hydrogen. The supported catalyst has been prepared by methods is. 2c. 3b and 3c of Table 2. Method 3c has received the most attention in the literature. It was felt that an appropriate cationic phosphine ligand could be substituted for PPh3 in the ip’pipp,gener- ation of the catalyst system. The cationic ligand should have a noncoordinating counter-ion such as BFn' or PF6- so that it will not interfere with the activity of the metal center. The supported catalyst might be generated by a number of methods. The hectorite could be exchanged with the cationic ligand to produce a phosphinated material which could react with either RhCl(PPh3)3. [RhCl(COE)2]2 or [RhCl(COD)]2. analogous to methods 3b or 3c (Table 2). Alternatively. the cationic catalyst might be generated pp'pypp. as above. and exchanged with the hectorite. similar to method 2c (Table 2). This last method may be the most .attractive. since it would allow the formation of a homogeneous catalyst of known composition. which should 19 retain its form when exchanged onto the support. There are a few examples of cationic phosphine ligands 1.9 in the literature. Quagliano. and coworkers. have prepared a series of high-spin. uncharged. four-coordinate species of the general formula. [Mx3(L+)]. where M = Co(II). N1(II). x =- Cl. Br. I and L... = [thrcszcnzrrhz CHzPh] or [thPCHzPPhZCHZPh]+. Analogous complexes of these two ligands show d-d electronic spectra which are nearly identical and. surprisingly. the spectra of [CoBr3(L+)7 and [CoBr3(PPh3)7- are almost superposable. For related studies see reference 50. Berglund and Meeks1 obtained similar results with Co(II) and Ni(II) complexes incorporating the ligand CR2 R3 112+ / :>c <21 /PPh This ligand was also2 used to prepare cationic. square planar. d8 complexes of Au(III) and Pd(II). [Au(L+)C13]Cl and [PdCL )2C12](C10,+)2.51b These diamagnetic complexes are electrolytes in solution. Other groups have shown that positively charged phosphine ligands give cationic species if substituted in Cr. Mo and W carbonyl compounds. The complexes {(CO)5 W[P(OCH2) 3PCH 3]}BF .52 [(C0) 52w"')]13F'1+ (thPCH%CH§P+Ph2CHgPh)BF“ 8(31) . 2.65 ddt 8(82) =- 2.09 dt 8(33) . “.37 d J a 6.1+. J = 14.5 32P+ H3P* [RhCl ( con) (thpcsécsgp*1>n2csgph)] Bra 8(31) - 3.72 m 8(32) 3 ”2.1 m |Hlb L 8(33) .. lune ( a“ HRM\/ 5(38) 3 5.“? 3 ga C1 8m") =- 3.12 s .IHB13+ a 1M0 Compare shcucomuph 8m“) = 5.52. 8(Hb) = 3.10 3). Chemical shifts are in ppm relative to TMS in 01301 at 25°. 3 Coupling constants are expressed in Hz. ’45 Figure 4. 36.43 MHz 311’ nmr spectra of P-P+BF4 (A). [BhCl(COD)(P-P+)]BFu (s) and O BhC1(COD)(PPh3) (C) at 28 in CH2C12. 1+6 B C L I 1 1 1 1 1 1 1 -60 -4o -20 0 +20 ppm FIGURE 4 47 with [HhCl(COD)]2 results in chloride bridge cleggage and the formation of two equivalents of HhCl(COD)(PPh3).+ Uhder the same reaction conditions the substitution of P-P BF“ for PPh3 produces the analogous cationic complex. [HhCl(COD)(P-F+L73Fh. The infrared spectrum of this complex. (Figure 3). contains most of the bands characteristic of the cationic ligand and BFu'. Bands due to Hh-COD and Hh-Cl stretching vibrations would be expected between 600-300 om-l and 300-200 om'l respectively.63 The proton nmr spectrum of [shc1(c00)(P-P*Llsru exhibits two sharp COD vinyl proton resonances which compare favorably in position with those observed for HhCl(COD)(PPh3) (Table 3) 36b.6h In addition. three resonances attributable to cationic ligand methylene protons are observed. although the one atv~2.1 ppm is not well resolved due to overlapping COD methylene proton resonances in the range 2.h - 1.9 ppm. The phosphorus-31 nmr spectra of [shc1(con)(P-s+x]ssh and HhCl(C0D)(PPh3) at +28° are shown if Figure u. The phosphorus chemical shift for the latter compound is -30.6 pm and JPBh :3 151 Hz. At +28°. [HhCl(COD)(P-F+)]BFu exhibits a five line pattern. It was expected that a first order spectrum would contain six lines consisting of a doublet of doublets near -31 ppm (where J a ~150 Hz and J P’ s<~46 Hz) for the PRh P phosphorus bound to rhodium (P) and a doublet near -27.1 ppm (JPP+ =r~#6 Hz) for the quaternized phosphorus (PI). The b8 absence of a doublet at +12.l ppm indicates that there is no free cationic.ligand in the solution. Comparison of Figure U(A) with “(3) shows that the three upfield peaks in the latter spectrum lie in the region expected for the 2+ doublet. The three upfield resonances cannot be considered a triplet since the two smaller peaks are not symmetrically disposed about the larger peak. First order analysis of any bonding scheme in which the cationic ligand retains its integrity and is bound to rhodium all predict spectra consisting of at least six lines. Moreover. the observed five line pattern cannot be rationalized in terms of any bonding configuration which might result if the integrity of the cationic ligand was destroyed on reaction with [HhCl(COD)]2 and/or solvent - either by oxidative addition of the phosphonium group to rhodium or by cleavage of the ligand's ethylene bridge or by quaternization of the trivalent phosphorus. Comparison of. the 31? nmr spectra of HhCl(COD)(PPh3) and P-PIBFu indicates that the difference in the expected chemical shift between P and P" for [HhCl(COD)(P-P+)]BF4 (~130 Hz) is smaller than the expected P-Hh coupling constant (~150 Hz). Complex nmr spectra are often observed for spin systems where coupling constants are larger than. or approximate the difference in chemical shifts between nuclei. In addition. complex spectra often appear deceptively simple. particularly in multispin systems where the coupling between two of the nuclei is weak.65 The 31? nmr spectrum of [HhCl(COD)(P-P*l]- BF“ is readily interpreted as an ABX splitting pattern in 49 which the coupling between Hh and P* is relatively small compared with JPHh and JPP+' As shown in Figure 5. the 31? nmr spectrum of [HhCl(COD)(P-P+)]BFu is also temperature dependent. Spectra below -80° were not recorded. so it is not known whether that is the limiting temperature. Since the -80° spectrum is not susceptible to first order analysis both the +280 and -80° spectra were submitted to the ABX spectral analysis technique 65 with the following results: at +280. outlined by Becker. 8? a -29.5 pm. 813+ = -27.3 ppm. JPHh = +iu9 Hz. JPP+ = +51; Hz and .1th ... +7 Hz. At -8o°. 8? = -31.8 ppm. 81"” = -27.3 ppm. JPHh 2 +153 Hz. JPP+ = +62 Hz and JP*Hh = -6 Hz. Despite the anomalous temperature dependent behavior of the cationic complex. the chemical shift of P is very close to that of PPh3 for the analogous uncharged complex. which does not exhibit a temperature dependent nmr spectrum. the JPHh values for the respective complexes are nearly identical. Although P-P+BFh is expected to be more basic and possess greater steric bulk than PPh3. it may be inferred from the 13 and 31? nmr data that. at least for HhCl(00D)L complexes. the cationic ligand interacts with the rhodium center to much the same degree. The ABX analyses were based on the following considera- tions in line with Becker's treatment.65 A. B and X correspond to the P. P+ and Rh nuclei respectively. The. (ab)+ and (ab)_ quartets were identified as peaks 1. 2. 3. 5 and 3. (b. h). 5 respectively for the +280 spectrum and the Figure 5. 50 1 Temperature dependent 3 P nmr'spectra of [HhCl(COD)(P-P+)]BFu. 0.1 g in 011201 The ~80° spectrum was obtained at twice the instrument gain of the others. 2. 5 ? , u fjwzfl FIGURE 5 52 difference between peaks 1 and 2 was taken as JAB (5“ Hz). 0 From the +28 spectral data; é JAX + JBx I3 78 Hz. 2D+ = 151 Hz and 2D_ = 5h Hz. These values allow only one possible solution fgr the set of values for (2A -'VB) and §(JAx - JBX) in the +28 spectral analysis. The (ab)+ and (ab)_ quartets in the -80° spectrum were identified as peaks 1, 2, 5, 6 and 3, h. 5. 6 respectively and the difference between peaks 1 and 2 was taken as JAB (62 Hz). From the ~80° spectral date. A: JAx + JBx = 73 Hz. 213+ = 250 Hz and 2n_ = 104 Hz. 0f the two solutions for the -80° ABX spectral analysis the one in which JPHh a +236 Hz and JP*Hh = -89 Hz was rejected since these values are much too large to consider as reason- able for the complex and ligand. B. Heterogeneous Systems I l. HhClSPPhBLBZHectI HhClngectJ P-P+/HectL RhCl 5 PPh 313 gP-P" (Hect , HhClBZP—P4. (Hect and [RhCl 3 cos) zlz/P-P+/Hect Although hectorite physisorbs the uncharged species HhCl(PPh3)3 and HhClB. both desorb from the support upon washing with an appropriate solvent. The HhCl(PPh3)3/Hect system is an active catalyst for the hydrogenation of 1-hexene in methanol. but much of the activity can be attributed to desorbed catalystirxsolution. the quantity of which increases as the reaction progresses. Filtrates taken from HhCl(PPh3)3/ Hect hydrogenation systems are yellow in color and exhibit a reactivity for l-hexene hydrogenation only one fourth less than the original activity. 53 In an effort to eliminate the desorption problem associated with these systems.-phosphinated hectorite. P-P+/Hect. was prepared by the exchange reaction between P-P+Br and Na*/Hect. It was felt that this material could be employed in the same way that phosphinated polymers and silica gels are used to prepare supported catalysts. as outlined in the reactions listed in part 3 of Table 2. P-P’ would serve not only as a phosphine ligand but also as the electrostatic binding agent for the otherwise neutral catalysts generated by this method. Aside from the prominent bands attributable to the mineral. the infrared spectra of mull samples of P-F+/Hect exhibit bands at 1&40 cm-1 and in the region 800 - 600 cm"1 characteristic of the ligand. albeit of lesser intensity. Although the concentration of P-P+ is high within the mineral. about 685 of the cation exchange capacity. x-ray diffraction analysis of P-P*/Hect powder indicated that at least a monolayer of additional solvent may be incorporated within the mineral interlayers under wet conditions (see Section III. C. 6). This should allow easier penetration by metal complex precursors to intercalated ligand sites. No detectable (color) amount of HhCl(PPh3)3 was supported on P-FI/Hect after 18 hours contact. It has been found that efficient displacement of PPh3 from this complex by polymer supported phosphines requires two weeks equilibra- tion time.15'31 No attempt was made to determine whether longer contact times would allow support of HhCl(PPh3)3 on 5b the phosphinated mineral since the other reactions listed in part 3 of Table 2 produce similar catalysts in.much less time. The addition of Hh013 to P-PI/Hect produces an orange- pink colored mineral which presumably contains either Hh(III) or Rh(I) phosphine complexes. These species do not appear to desorb (color) from the phosphinated hectorite. Addition of hydrogen produces a very light yellow material. This color change is characteristic of the formation of Hh(III) dihydride phosphine complexes. but even though phosphinated polymer supported HhCl3 is an active hydrogenation cata- lyst.27°’3°a'°’3 HhClBIP-P+/Hect proved to be inactive for the hydrogenation of 1-hexene. A rationale for this in- activity is provided in Section III. C. 2. Exposure of [HhCl(COE)2]E to phosphinated hectorite over short periods of time (minutes) produces a yellow material which presumably contains rhodium(I) phosphine complexes (see the last reaction listed in part 3b of Table 2). The yellow color cannot be washed from the mineral. However. [HhCl(COE)2]é/P-F+/Hect was also inactive for the hydrogen- ation of 1-hexene in methanol. although it lightened in color on addition of hydrogen. A rationale for the inactivity of ... [HhCl(COE)2]E/P-P /Hect is provided in Section III. c. 2. 2. shgong-P+[Heet, thozgsect, thozgggol, and Rh 0 SILG 4. During the course of the work on theflHhCl(COE)2]2/P—P / Hect systems it was found that prolonged contact (hours) of [HhCl(COE)2]% with P-F+/Hect resulted in the formation of 55 a dark gray material. The cause of the dark gray color was deduced to be supported rhodium metal since this material is not only an efficient catalyst for the hydrogenation of 1-hexene but. like other supported Hh(O) catalysts.66 it hydrogenates benzene as well. The zero valent rhodium cannot be washed from the mineral. Although the mechanism remains uncertain at this point. the formation of Hh(o) appears to result from surface catalyzed disproportionation of [HhCl(COE)2]é. which produces Hh(O) and Hh(III) species. Rhodium metal is precipitated after a period of months from methanol. methylene chloride or benzene stock solutions of [Hhc1(cos)2]§ stored under N2 in pyrex flasks. The originally light yellow solutions change to a deep yellow or orange-red color during this process depending upon the initial concentration. a color change 'characteristic of the formation of non-phosphinated Hh(II) species. especially HhClB. Hh(O) formation occurs within hours. however. when [HhCl(COE)2]é is brought into contact with natural hectorite. kaolinite or silica gel. (Kaolinite is an alumina-silicate mineral composed of alternating layers of aluminum and silica.) The resulting Hh(0) materials. Hh(0)/Hect. Hh(0)/Haol and Hh(0)/SILG. are all excellent catalysts for the hydrogenation of 1-hexene and hydrogenate benzene as well. The rhodium metal does not wash free of the support. either prior to or during the course of hydrogenation experuments. The activities of these metal supported catalysts 56 compare favorably with the commercial catalyst. 5% Hh/Alzo3 (see Table 4). The rate behavior of the catalysts for l-hexene hydrogenation is typical of supported metal catalysts.66 During the course of the reaction the initial rate is the fastest and is maintained until at least 75$ hydrogenation. when the rate decreases as a result of decreased substrate concentration. One possible rational- ization of the lower activity of the smeetite catalysts may be that each specific support allows only a certain degree of rhodium metal aggregation - isolated atoms 15. clusters -~ resulting in differences in the nature of the active sites between the catalysts. 3. EasiZMont and [RhCl(COE)2jg[§aSi(§ont Silylation of surface hydroxyls appears to inhibit the [HhCl(COE)2]§ disproportionation reaction. The edges of the silicate sheets in smectites contain surface silanols which can be silylated with a 2:1 mixture of (MeZSi)2NH and he33ic1. [HhCl(COE)2]2 may be exposed to silylated montmorillonite for days before any observable dispropor- tionation occurs. Montmorillonite is structurally related to hectorite but contains Al3+ ions instead of Mg2+ ions in the octahedral sheets. No attempt was made to prepare a phosphinated derivative of silylated montmorillonite or hectorite because of the lack of success in producing catalytically active materials .with phosphinated hectorite as a support for rhodium- phosphine complexes. However. silylation offers an attractive 57 Table h. Initial Hydrogenation T0#'s for Supported Hh(O) Catalysts Catalyst Substrates Loading 1-Hexene Benzene mmol Hh(0.2 g Hh(0)/P-P+/Hect 391 1 0.03 Hh(0)/Hect 393 1 0.03 Hh(0)/Kaol #13 NA ' 0.05 Hh(0)/SILG 1301 V 5 0.01 5% Hh/A1203 1010 NA T0#'s reported as ml Hz/min/mmol Hh at 10% hydrogenation. Conditions: Substrates 1 g in.methanol. 0.2 g catalyst in 30 ml total volume at 25° and atmospheric pressure. The 55 Hh/A1203 result is taken from reference 67. 58 method for protecting catalysts and substrates from surface silanol interference. Naturally. there may be situations when the presence of surface hydroxyls is a desired feature. but if reactions of known homogeneous catalysts are to occur exclusively in interlayer space. the disruptive silanol interaction may be minimized through silylation. This is particularly important for systems which would utilize moisture sensitive organometallics. which are known to bind 9f,h,2#.68 hydroxyls of silica gel and alumina. C. Homogeneous Systems Unlike [HhCl(COH)2]2. [HhCl(COD)]2 is stable toward disproportionation and may be stored in solution under oxygen free conditions for long periods of time. Tqui has ngpared RhCl(PPh3)3 from [HhCl(COD)]2 and excess PPha. and a number of workers. have utilized [Hhcucom]2 as a precursor in the preparation of polymer and/or silica bound rhodium-phosphine complex catalysts.26a'o'27f'30b'c'3'3“ Although the initial studies with phosphinated hectorite were unsuccessful in generating mineral bound cationic catalysts. it was felt that if a cationic rhodium phosphine catalyst employing the positively charged ligand could be generated $3.2;33. it might be possible to bind this active species by direct exchange with the mineral. Methanol was chosen as the solvent system for these studies. Benzene is generally the solvent of choice for ~Wilkinson type catalysts but methanol was chosen because the cationic ligand is not soluble in nonpolar solvents. 59 Methanol is also capable of swelling hectorite interlayers. thus providing a.more solution-like environment for mineral bound complexes. Wilkinson's catalyst has not been employed for the hydrogenation of olefins in methanol previously. due to its low solubility in this solvent. As a result it was necessary to investigate the general catalytic behavior for 1-hexene hydrogenation of Wilkinson's catalyst generated from [HhCl(COD)]2 and an appropriate number of moles of PPh3 in order that legitimate comparison of this catalyst might be made with those incorporating P-F+BFu. 1. Hydrogenations Employing 0.x.l P-Pl’spuspphagg Catalysts The variation in catalytic activity as a function of the PPhBaHh ratio was studied for the [HhCl('COD)]2 - PPh3 system in methanol. It was assumed. based on previous work with analogous systems.u7 that the combination of stock solutions of [HhCl(COD)]2 and PPh . followed by addition of hydrogen. 3 would reduce con to cyclooctene y;g_rhodium hydride inter- mediates prior to formation of the desired catalyst. according to the following reaction. vlrfiihcucomj2 + x(PPh3) + H2 —> HhHZCl(PPh3)x 4- 081116 The results for the l-hexene hydrogenation activity of the systems employing PPhaxnh ratios from 6:1 to 031 are presented in Table 5. These results complement the findings of other workers in this area.“7 A 2:1 PPh th 3 ratio produces the most active catalyst. favoring 60 .«.oom« I :m.ozouomld .ANNAQOUVHosmNV AHvsm HOSE No.0 .Hhou 0:5 .omN .oESHOP Hope» H8 on .nmommov_fi H .0:0HOMtH n oudhpmnam .Asm Hoaa\cda\mm Hay *oa Aemm,~ua asses: esuoa douse . soaoosom oz. a.o.o Anooon nonsense no names onsm scream. mm on a.a.o . e as on has one ens can n.n.a.e mm so ass can own sen no: man can a.~.o ans ass was sou can emu «an new New H.n.o mm an an no one was and was and a.s.o <2 as we on we so on «.m.o <2 mm mm mm on mm mm a.o.o com com (mom. can con so: can can con sm.msma.+a-a . Asov Hoboshaa am~%mmmw . .mmummmmm mpnhdopmo :o«uosomoaohm «.N.o hon m.‘os .n canoe 61 coordinatively unsaturated intermediates such as HhCl(PPh3)2 and HhH2C1(PPh3)3. Increasing the PPh :Hh ratio results in 3 a loss of activity due to the competition of excess PPh3 with substrate for coordination sites at the metal center. The loss of activity at PPh :Hh ratios lower than 2:1 was 3 at one time attributed to the formation of a catalytically 1+ inactive dimeric species. 7a [HhCl(PPh3)2jE. but Tolman has recently shown that the dimer is a good catalyst for olefin hydrogenation.“7c Rhodium complexes containing less than two phosphines may either be unable to activate molecular hydrogen. or they may form tightly bound olefin complexes which are incapable of reductive elimination under hydrogenation conditions. [HhCl(COD)]é. in the absence of PPh}. is not a catalyst. but it is slowly reduced under hydrogenation conditions to rhodium(O). an excellent olefin hydrogenation catalyst. 2. dro enations Em lo in Y:X:1 P-P+BF :PPh Catalysts The combination of various quantities of P-P+BFu and [HhCl(COD)]2. followed by exposure of the resulting solutions to hydrogen. does not produce species capable of acting as catalysts for the reduction of 1-hexene. As seen in Table 6. the systems derived from P-F+BFu:Hh ratios of 1:1. 2:1 and 3:1 were all inactive. The cationic ligand might be expected to be more basic than PPhB. Wilkinson has found that ligands of’much higher basicity than PPh generally afford less h f active hydrogenation catalysts. In fact. at a phosphine:Hh 62 .a.ooms n sm.osowomua .xfimanoovaosmgv AHasm Hoes ~o.o .eeoo can .omm .essaoe assoc as on .xmommov m." .osowom:s u easeoensn .xsm Hossxsasxmm Ha. nos mam son «on emu new mom awn own new a.~.~ can can now emu mom can can man so: a.~.a 42 me so «an an“ no on H.a.~ mm :0 an mm :m mm mm ca no a.«.a Azxm ozv a.o.n xzxm oz. a.o.~ Azxm ozv a.o.a com com com, com can so: can can con sm.msaa.+a-a «so. asbestos amammmmm .mmawmwmm mpmhamuoo coauoaowoaohm «.x.a you m.*oa .0 Dance 63 ratio of 2:1 the PEt3 system shows very little activity. but PPhZEt (which should have nearly the same electronic proper- ties as the cationic ligand) is highly active. At a phosphine:Hh ratio of 2.1 the PthEt system is only one tenth less active than the PPh system. As a result. electronic effects alone cannoz explain why P-F+BFu is a poorer ligand for olefin hydrogenation than PPhB. The primary difference between P-F+BFu and PPh3 is one of steric bulk. PPh3 is generally considered to be quite bulky. but comparison of space-filling models of the two ligands indicates that. regardless of the conformation about the ethylene bridge. P-P+BFu should be much.more bulky than PPhB. Tolman has enumerated some of the effects on the activity and selectivity of homogeneous catalysts as the size of the substituents on phosphorus ligands increases.69 In general. smaller ligands in competition for coordination sites with the bulky ligands are usually bound preferentially. and less crowded isomers are favored if the possibility of different isomers exists. Further. both increases in the rates of phosphorus ligand dissociative reactions and decreases in rates of associative ones are observed as the ligand size increases. If the phosphorus ligands are particularly bulky. they can often interfere with or prevent the coordination of other ligands which would normally be strongly bound. for example. 00, 02 or Cth. This is especially true if there are two or more larger ligands in the coordination sphere of the metal. All of these effects. 64 in combination with the electronic requirements of the system. contribute to the reactivity patterns of homogeneous catalysts. The yellow 2:0:1 and 3:0:1 systems do lighten in color on exposure to hydrogen. characteristic of the formation of Hh(III) dihydride complexes. However. the 2:0:1 and 3:0:1 catalysts must be so crowded at the metal center that coordination by olefin. followed by metal alkyl formation and reductive elimination of product. is sterically hindered. The inactivity of the 1:0:1 system is not surprising in view of the behavior of the 0:1:1 catalyst. In view of the results with these homogeneous systems. it is not surprising that the heterogeneous systems employing phosphinated hectorite as a support were inactive as olefin hydrogenation catalysts (Section III. B. 1). The complexes formed within the interlayers of P-F+/Hect should be little different from the 1:0:1. 2:0:1 and 3:0:1 homogeneous species. Combination of the cationic ligand with a less bulky phosphine ligand should and apparently does reduce the steric crowding at the metal center sufficiently to produce an active hydrogenation catalyst. A 1:1:1 ratio of P-P+BFu: PPh3:Hh affords a catalyst of good longevity but of much lower activity than the analogous 0:2:1 catalyst (Tables 6 and 5). The lower activity of this system can be attributed to the steric and electronic effects discussed earlier. The probable bonding configuration of this catalyst is discussed in the next section. 65 2.1.1. 1.2.1 and 2.2.1 ratios of P-P+BF4:PPh :Hh also 3 afford active homogeneous catalysts (Table 6). The 2:1:1 catalyst is interesting in that. as expected from comparison of the 0:2:1 and 0:3:1 catalysts (Table 5). addition of another mole of P-P‘d'BF'I+ decreases the initial rate due to phosphine competition for olefin coordination sites at the metal center. However. the complexes must undergo ligand redistribution reactions because during the course of the reaction the rates increase. Formation of small amounts of ”HhCl(PPh species should increase the rate since this 3’2" would be the most active catalyst in the solution. Consideration of the results for the 1:2:1 system indicates that less bulky PPh3 must be able to compete for coordination sites much more efficiently than P-F+BFh. The resulting catalyst system is nearly as active as the 0:2:1 catalyst and more active than the 0:3:1 system. The major species in solution no doubt resemble those of the 0:2:1 catalyst. the cationic ligand competing only moderately well compared to PPh for olefin coordination sites on the metal. The 2:2:1 catalist is simply an extension of the 1:2:1 system in which an additional mole of P-PIBFu has been added. The 2:2:1 catalyst is much.more active than the analogous 0:4:1 system. again indicating that P-P+BFu is less able to compete for coordination sites than PPh due 3 to its large steric bulk. 66 3. Characterization of Catalyst Precursors A phosphorus-31 nmr study was undertaken in an effort to better understand the nature of the homogeneous catalysts. Of particular interest were those catalysts derived from 0:2:1 and 1:1:1 P-P*BFu:PPh3:Hh ratios. The 0:2:1 catalyst is generated by the sequential addition of PPha. H2 and 1-hexene to[IHhCl(COD)]2 as represented below. icl'Hhclmonu2 4- PPh —) I I + PPh3 -’ II II + H2 -) III III + 1-hexene -€> IV 3 It was felt that 31F nmr analysis of these four steps would allow characterization of the catalyst precursors and the major components of the catalyst solution. CH'2Cl2 was used as the solvent in these studies since good spectra could not be obtained with methanol due to the limited solubility of [HhCl(COD)]2 and most other catalyst precursors in that solvent. As described in Section III. A. and in the literature.58'6u PPh3 cleaves the chloride bridge of [HhCl(COD)]2 to produce BhC1(COD)(PPh3) at a 1:1 PPh :Rh ratio. 3 J.:L’Hh01(con)]2 4» PPh -9 RhCl(C0D)(PPh3) (I) 3 The phosphorus chemical shift for I in CHZClz is -30.6 ppm and JPHh a 151 Hz. These values may be obtained either from the generation of I in situ or from the dissolution of solid I. Addition of another equivalent of PPh to I produces 3 67 solution II. The temperature dependent 31F nmr spectra of II are reproduced in Figure 6. The doublet of triplets at BPc :- -I+7.8 ppm (.11,th = 193 Hz. JPcPt = 39 Hz) and the doublet of doublets at 8Pt = -31.2 ppm “’1th = 146 Hz) are characteris- tic of HhCl(PPh3)3 (11t.47c 5Pc a -48.9 ppm. 81": =- -32.2 ppm. JPcHh = 192 Hz. JPcPt = 38 Hz. thRh = 146 Hz). PO is the phosphorus cis to the two trans phosphines. Pt' in the roughly square planar complex. The resonance at 3P a +7.1 ppm may be attributed to free PPh3 (lit.u7° 5Pu+6 DP!!!) . The same spectral features were observed for II when toluene or CHZCIZ were used as the solvents. Addition of two equiv- alents of PPh3 directly to é[HhCl(COD)]2 also generates II. The presence of HhCl(PPh3)3 in solution II was a surprising result. Proton nmr studies have shown that HhClI.3 complexes are produced on addition of L to HhCl(COD)L. where L equals the more basic. less bulky ligands PPhZMe. PPhMe2 and PBua.7o presumably according to the following scheme. HhCl(COD)L + L ;== HhCl(COD)L2 z== HhCl(COD*)L2 HhCl(COD*)L2 + L 2:: HhCl(COD*)L3 ;;=; HhClL3 + COD COD’ represents monodentate 1.5-cyclooctadiene. The overall reaction might be represented as follows. zshcucomr. + 21. -) HhczlL3 + HhCl(COD)L + 000 Hewever. proton nmr studies of the addition of one equivalent of PPh3 to HhCl(COD)(PPh3) in CHCl3 have not provided any evidence for HhCl(PPh3)3 formation. The observed temperature dependence of the COD vinyl proton resonances 68 Figure 6. Temperature dependent 31'P nmr spectra of HhCl(COD)(PPh3) 4- PPh 0.03 g in 0H2012. 3. + 30° ... 290 -4E> - -20 ppm FIGURE 6 70 from ~60° to 00 has been attributed to a phosphine exchange pr°°°33 1nV°1V1n6 a pontacoordinate intermediate.6b’7o HhCl(COD)(PPh3) + PPh3 : HhCl(COD)(PPh3)2 The distinct vinyl proton resonances observed at low temperature for HhCl(COD)(PPh3) broaden and coalesce as the temperature is raised. No free COD was observed in the proton nmr. 331 Th P nmr spectra show the presence of HhCl(PPh 3’3 and free PPhB. HhCl(PPh3)3 appears to be a stable complex over the temperature range studied but the free PPh appears 3 to be in rapid thermal equilibrium with a second phosphine containing species. If HhCl(PPh HhCl(COD)(PPh3) and 3’3' COD are present in solution following reaction. an equilibrium might be set up between HhCl(COD)(PPh3) and COD such that free PPh3 and HhCl(COD)2 are favored at lower temperatures. RhCl(COD)(PPh3) + COD : RhCIJCOD)2 + PPh3 It was found however that addition of one equivalent of free COD to HhCl(COD)(PPh3) produced no apparent change in the 31P spectrum of the complex between +300 and -80°. Similarly. Vrieze found that the proton nmr spectrum of HhCl(COD)(PPh3) was unaffected by addition of excess COD. although only the temperatures between +250 and +600 were studied.6u It is possible that HhCl(PPh3)3 may serve to activate the exchange between COD and PPh3 in some way. Although HhCl(COD)2 has not been observed spectroscopically nor has it been isolated. the analogous norbornadiene complex. HhCl(NBD)2. has been observed in cold solutions of 71 71 and the butadiene complex. HhCl(CuH6)2. has been isolated.72 At higher [HhCl(NBD)]2 containing excess NBD. temperatures. HhCl(COD)(PPh3) may not be observed by 31? nmr since the peaks attributable to it at -30.6 ppm may be overlapped by the doublet of doublets arising from HhCl(PPh3)3 at -31.2 ppm. Although the hypothesis that HhCl(COD)2 is present with HhCl(PPh3)3 and free PPh3 in solution II does account for the observed 31F nmr spectra. it contradicts the proposed interpretation of the 1H nmr spectra. This inter- pretation requires that HhCl(COD)(PPh3) be present at low temperature. along with free PPh3.6u’7o The existence of HhCl(PPh3)3 in II defies this interpretation based on problems of stoichiometry. although it may be possible that the vinyl protons of HhCl(COD)2 have the same chemical shifts as those of HhCl(COD)(PPh ). 3 The discrepancies between the 1 H and 31p nmr results are difficult to rationalize. The preparation of the compounds and solutions is essentially the same. The concentrations of the solutions used for the 1H and 31P nmr studies were of the same magnitude. Elucidation of the nature of the HhCl(COD)(PPh3) plus PPh system probably requires a more rigorous. independent 1H. 1P and perhaps 130 nmr study in addition to conventional product separation and analysis. Addition of hydrogen to solution II produces solution III. The temperature dependent 31? nmr spectra of III 72 are reproduced in Figure 7. The -280 spectrum may be characterized in the following way. The downfield incom- pletely resolved doublet of doublets at SPt = -40.1 ppm (JPtHh = 115 Hz. JPtPc = 18 Hz) and the upfield unresolved doublet of triplets atlaPc = -19.4 ppm (JP Hh = 90 Hz) are 47c c characteristic of HhH2C1(PPh3)3 (lit. Spt .. 410.3 ppm. = - e I = u = 3 8pc 20 7 ppm JPtRh 11 Hz. thpc 18 Hz and .7},th 90 Hz). Chemical shifts and coupling constants were taken from expanded scale spectra. The doublet centered at BP = -30.6 ppm ”PM = 151 Hz) is characteristic of HhCl(COD)(PPh3) (see Section III. A). Alternative peak assignments are difficult to rationalize. The temperature 47c dependence of the spectrum.of HhHZCl(PPh is well known. 3’3 The line broadening and loss of coupling at 280 is due to exchange of the labile phosphine cis. PC. to the two trans phosphines. Pt‘ Apparently. hydrogen adds directly to RhCl(PPh3)3 to form Hh3201(PPh3)3. Although a go analysis for reduction products of COD was not made. the presence of HhCl(COD)(PPh3) at both high and low temperatures indicates that the ' equilibrium. RhC1(COD)(PPh3) + COD {-3 RhCl(COD)2 + PPh}. is not operative. RhHZCl(PPh3)3. most likely in the highly active dissociated form. HhH2C1(PPh3)2. probably acts as a catalyst for the reduction of the free mole of COD in the solution. Addition of a quantity of 1-hexene sufficient for ten 73 Figure 7. Temperature dependent 31F nmr spectra of BhC1(COD)(PPh3) + PPh + 13 3 2. 0.03 M in CH2C1 2. 7t: WM -280 Nut/LIAM. I I I I 1 _ ‘20 0 +20 I I I I ppm FIGURE 7 75 catalyst turnovers under oxygen free conditions followed by addition of H2 until no more uptake was observed on a hydrogenation apparatus produced solution IV. The temper- ature dependent 31F nmr spectra of IV are shown in Figure 8. In the -610 spectrum the upfield distorted doublet of doublets at 8st = -31.0 ppm (J = 146 Hz. JP P = 39 Hz) PtHh t and the slightly obscured doublet of triplets at ch = -47.6 ppm (JPcBh = 192 Hz) are characteristic of RhCl(PPh3 3. The large doublet downfield at 8? = -51.5 ppm (JPRh = 195 Hz) is characteristic of chloride bridged dimeric species such as [HhCl(PPh3)2]2 and [HhCl(olef1n)(PPh3)]2. (See later in this section.) The absence of hydridic species indicates that the reduction of 1-hexene was incomplete so that there is probably residual olefin in solution IV. The fact that HhCl(PPh3)3 remains as one of the major species is a surprise. For a phosphine to rhodium ratio of 2:1 it was expected that the major species in solution would contain only two phosphines in the metal's coordination sphere. The tris phosphine complex is apparently relatively more stable than the other his and mono phosphine complexes possible in this solution. The complex upfield.patterns in the higher temperature spectra of IV are difficult to interpret based on first order spectral analysis. The equilibrium process illustrated below might account for the observed temperature dependence as well as the stoichiometry of the system. although it is difficult to say with any certainty what the HhCl(L)(S) Figure 8. 76 1 Temperature dependent 3 P nmr spectra of HhCl(COD)(PPh3) + PPh3 + xH2 + y(1-hexene) 0.03 g in CH Cl The +30°, 42° and -61° 2 2' spectra were taken at twice the instrument gain of the +1° and -210 spectra. +30° WWW )7) N} j W WWWMWN +|° 2 4 2 77 ELM; Thaw/LN J ‘60 Oppmz FIGURE 8 78 species may be because the composition of this solution has not been adequately elucidated. HhClIL)(S)2 F? t[11hCl(L>($)]2 4- s 3 may be solvent or residual olefin. It is interesting to note that the complexes HhCl(COD)(PPh3) (8? = -30.6 ppm. JPBh = 151 Hz) and HhCl(CzH,+)(PPh3)2 (5P = -35.7 ppm. JPHh = 128 Hz)“7c would both give rise to resonances in the vicinity of the complex upfield pattern of IV. Despite the fact that HhC1(PPh3)3 and [HhCl(PPh3)(S)]2 appear to be the major species in the solution they are probably not the actual catalytic species. They are probably in dissociative/associative equilibrium with the highly active species HhCl(PPh3)2 and/or HhH2C1(PPh3)2 which have been invoked by numerous authors to account for the observed kinetics in analogous catalyst systems.“7 A 31F nmr study of the 1:1:1 catalyst system was undertaken in order that a comparison might be made with the analogous 0:2:1 catalyst system just described. The 1:1:1 catalyst is generated by the sequential addition of 12-19313“. PPh3. H2 and 1-hexene to [HhCl( 0013)]2 as represented below. i:[HhCl(Cop)]2 + P-P+BFQ —) I' I' + PPh3 -€> II' II' + H2 -€> III' 111' + 1-hexene '-€} IV' As described in Section III. A. the addition of one equivalent of P-P+BFu to i.[1ihCl(Cop)]2 produces 79 [HhCl(COD)(P-P*)]BF . (I'). analogous to the preparation of I. HhCl(COD)(PPh3). Addition of one equivalent of PPh3 to I' produced solution 11'. The temperature dependent 31F nmr spectra of II' are reproduced in Figure 9. The addition of PPh 3 to [HhCl(COD)]2 followed by addition of P-P+BFu produces 31 a solution whose P nmr spectra resemble those of solution 11'. The spectra are too complex to allow direct assignment of the peaks: however. certain major features of the spectra deserve comment. The large peaks near -27 ppm are in the region expected for the phosphonium group resonances of the cationic ligand. The two multiplets found between -40 and -50 ppm are reminiscent of the doublet of triplets found for 5P0 = -47.8 ppm of solution II and are therefore indicative of tris phosphine complexes in II'. The resonances between -20 and -35 ppm. aside from those due to the phosphonium group. are found where the trans phosphines of HhClI.3 complexes should resonate as well as the phosphine resonances due to HhCl(COD)L complexes. Like the spectra for II. II' shows the presence of free phosphine as the temperature is lowered. although this occurs at much lower temperature. It may be inferred from these generalizations that solution II' is similar to solution II in many ways. but the species present are much more complex since there are a number of ways in which the two different phosphine ligands may be distributed among them. Addition of hydrogen to solution 11' produces 80 Figure 9. Temperature dependent 31F nmr spectra of [HhCl(COD)(P-P+)]BFI+ + PPh 0.03 g in 30 WI Lea m NM M VJ kw“ I I I I I I I I I '60 '40 “20 0 +20 ppm FIGURE 9 82 solution III'. The temperature dependent 31F nmr spectra of III' are reproduced in Figure 10. These spectra are also too complex to be able to make specific peak assignments but just as the spectra of II' had certain features in common with II. III' appears to mimic the properties of III. The large central peaks near ~27 ppm may be attributed to the phosphonium group of the cationic ligand. The broad multiplets near -41 ppm as well as those near -19 ppm may well indicate the presence of HhHZClL3 complexes. where L is PPh) and/or P-PIBFu. There are also peaks centered about ~30 ppm which may be due to HhCl(COD)L complexes. As with 11'. it is difficult to determine precisely which species are present in solution III'. but the appearance of the spectra is suggestive of complexes similar to those found in solution III and probably containing mixed phosphine ligands. Addition of l-hexene to III' caused immediate precipitation of most of the rhodium containing material from the solution. The residual catalyst hydrogenated the i-hexene only very slowly. The precipitation of most of the cationic catalyst precluded meaningful analysis of the 31F nmr spectra of this solution. Although [HhCl(COE)2]E was not used as a homogeneous catalyst precursor in this study. it was of interest to compare its reactivity toward PPh3 and P-P+BFu with that of [HhCl(COD)]2. Addition of one equivalent of PPhB to 83 31 Figure 10. Temperature dependent P nmr spectra of [HhCl(COD)(P-p+)]BFu + PPh3 + Hz. 0.03 31 in CHZCIZ. ”Lyle/“W . “52° 1 I J ‘60 I 1 1 -4 .- I (hm... * PPm _ FIGURE IO 85 §[HhCl(COE)2]é is known to cause displacement of one equivalent of COE by PPh3.7u not chloride bridge cleavage as is the case for [HhCl(COD)]é. i[HhCl(C0E)2]2 + PPhB —) alri’Hhcucos)(1>Fh3)]2 + com The 31F nmr spectrum of [HhCl(COE)(PPh3)]2 is shown in Figure 11 A. 8F = -55.2 ppm and J ... 194 Hz. It is PRh assumed that one equivalent of COE is displaced from each rhodium center in the dimer. It is not known whether the configuration of the two phosphines about the Hh(Cl)ZHh linkage is cis or trans. Addition of two equivalents of FFh3 to §[HhC1(C0E)2]2 is known to cause displacement of two equivalents of COE 47c.74 3. ifshcucomzjz + 2PPh by PPh 3 -> t[1athl(FFh3)2]2 The 31F nmr spectrum of [HhCl(PPh3)2]E is displayed in + 200E Figure 11 B. 8F = -51.5 ppm and J = 199 Hz. This PRh dimer is not very soluble in CHZCl2 or benzene (~3 x 10"5 fi).u7c and it began to precipitate from the 0.05 5 solution within one hour following preparation. The 31F nmr data for the much more soluble complex (HhClL2)2. where 47c L = P(p-tclyl)3. are 8P :2 49.5 ppm and J = 196 Hz. PBh Addition of three equivalents of PPh3 to §[HhCl(COE)ZJE not only displaces two equivalents of COE but also cleaves the chloride bridge of the dimer forming HhCl(PPh3)3. ithCl(COE)2]2 + 3F1>h3 -) HhC1(FFh3)3 + 200s. The 31F nmr spectrum of HhCl(PPh3)3 is reproduced in Figure 11 0. BF = -31.5 ppm. 8F = -48.3 ppm. 86 31 Figure 11. P nmr spectra of CHZCl solutions 2 containing. A. §[HhCl(COE)2]% + PPh3: B. ithCl(COE)2]E + 2PPh3: and C. §[HhCl(COE)2]é + 3PPh A and B. +28° 3. C. -34°. 87 ppm FIGURE II 88 JPtHh = 145 Hz. JPth 8 194 Hz and J = 38 Hz. Tolman has shown that (HhClL PtPc 2)2 and HhClL3 may be generated in an analogous fashion from the addition of phosphine to Cramer's complex. [HhCl(CZH,+)2]2.u7c (HhClL2)2 adds one equivalent of hydrogen to produce H2(HhClL2)2 which is an active hydrogenation catalyst and is in dissociative equilibrium with the highly active species 'HhClLZ” and HhHZCle. HhClL3 adds one equivalent of hydrogen to produce HhHZClLB. which dissociates one equivalent of L to form the catalytically active intermediates. Although the 2:1 PPh3:Hh catalyst generated from [HhCl(COD)]é contains HhCl(PPh3)3 as well as dimeric species. this presents little problem for the catalyst since active species containing two equivalents of PPh are easily obtained. Overall 3 hydrogenation rates may be affected. however. It would be interesting to see whether HhCl(PPh3)3 species are generated in 2.1 PPh3:Hh catalyst solutions obtained from [HhCl(COE)2]E. The cationic ligand. P-P+BFu. appears to mimic the behavior of FFh3 in the [HhCl(COE)ZJE system. Addition of one equivalent of P-P+BFh to é[HhCl(COE)2]é produces &[HhCl(Cos)(P-F*)]2(3Fu)2 [HhCl(COE)2]E + 2P-P+BFu -4> [HhCl(C0E)(F-F*)]2(BFu)2 + 2003 The 31P nmr spectrum of [HhCl(COE)(P-P‘+)]2(BF5)2 is shown in Figure 12. 8F = -51.8 ppm. 815" = -27.1 ppm. J = 195 Hz PHh and J a 45 Hz. It is not known whether the configuration FF+ of the two phosphines about the Hh(Cl)ZHh linkage is cis 89 Figure 12. 31P nmr spectrum of [HhCl(00E)(F--F"’)]2(13FL,)2 at +28°. 0.05 g in CH2C12. 9O F ppm IGURE I2 91 or trans. D. Heterogeneous Systems II. fiydrogenations Employigg .1_:_1_:_1/Hect L 0. 2 . 1/Hect , Hh( COD) (PPhBlquHectl 2:0:1/Hect and 3:0:1/Hect The system employing a P-P‘BFu:PPh3:Hh ratio of 1:1:1 appeared to be best suited for use as a cationic catalyst since the 1:0:1. 2:0:1 and 3:0:1 systems failed to function. the 2:1:1 system appeared to undergo constitutional change during reaction and the 1:2:1 and 2:2:1 systems probably contain too high a concentration of neutrally charged species. It was felt that generation of the hydride of the homogeneous catalyst prior to exchange with hectorite would allow a more legitimate comparison between the homogeneous and heterogeneous systems. since the nature of the reduction of the COD precursors might be altered within the mineral environment. Methanol was used as the solvent system to maintain consistency between the heterogeneous and homogeneous catalyst environments. As may be seen in Table 7. the 1:1:1 homogeneous catalyst. when exchanged on hectorite. 1:1:1/Hect. is an active catalyst for the hydrogenation of i-hexene. In fact. the supported catalyst is much.more active than the homogeneous system. In general. the rate decrease of the 1:1:1/Hect system during the reaction parallels that of the solution catalyst. No desorption of the catalyst occurred during the reaction (color). Independent tests of filtrates taken from the reactions at CT = 750 and CT = 1300 for 92 .H.ooma u sm.o:ouomla .AHvsm HOSE No.0 .msoumam ones» you oobhomno no: soduahonoo unmaoudos .eeoo can .onm .ossaot Home» as on .Amommov m a .ozonomld u oudhumnsm .Anm HOEE\:«E\Nm HEV ‘09 .sm.n£mm.+mlm u fl.x.w Azxm oze poem\a.o.m Azxm ozv poom\H.o.~ me an ass was +~Ansaaexoooesm mm one was mad encom\+mxmsmavxooo.sm mm as are new smm ram nos man one a.~.o 42 as and man was «as no: man mmm epoom\«.~.o on so as on an no no on no H.H.a no . no mna and and «as and and ass soom\a.a.a com com com one cow, so: can con cos condense AaoM hoposusa umxamumo mamaampmo nodumsowonohm poem \+Nan:mmvanoovsm Ugo poom\d.m.o 80% m.*OBzH= .mnmhddumo soapssomoaoam +~Ansamvaaoovsm one a.~.o .H.H.a .ooom\a.a.a sou n.*oa .5 sense 93 olefin hydrogenation activity gave negative results. The fact that the rates of the heterogeneous and homogeneous systems parallel one another is significant. It indicates that the species responsible for the catalytic activity in both systems are probably very similar in composition. It is interesting to note that the composition of the 1:1:1/Hect catalyst determined by chemical analysis gave a Hh:P:Cl ratio of 1.00:3.17:0.76. very close to the ratio of l.00:3.00:1.00 expected for the overall composition of the homogeneous catalyst. That the catalyst exhibits larger TO#'s in the supported environment is unusual for Wilkinson type catalysts. which generally exhibit decreased activity when immobilized.9 The solution-like environment expected for the catalyst within the hectorite interlayers should allow the catalyst to behave as it would in the homogeneous environment. but although this is no doubt a major factor. it cannot explain the increase in catalytic activity. However. each of the following rationalizations may be contributing factors. either in part or in combination. It is possible that in the mineral environment steric congestion at the metal center may be relieved if strong electrostatic attraction of the silicate sheets for the phosphonium group causes the cationic ligand to undergo conformational change about the ethylene bridge by pulling the phosphonium group away ~from the coordination sphere. In addition. it is possible that the randomly distributed sites of negative charge 94 within the mineral. at a catalyst loading of only 14$ that of the cation exchange capacity. affect the distri- bution of dimeric species in the overall catalyst composition. Separation of the rhodium centers through phosphonium group association with the negatively charged sites of hectorite would promote dimer separation and inhibit dimer formation. This should result in a higher concentration of the more active monomeric species. ”HhCILZ" and HhHZCle. As shown if Table 7. 0:2:1/Hect and Hh(con)(FFh3)2+/Hect were tested for catalytic activity in comparison with’their homogeneous counterparts. 0:2:1/Hect begins to desorb catalyst immediately upon suspension in the solvent. Early in the work it was feared that the negatively charged silicate sheets might promote chloride ion dissociation from the rhodium center in the wilkinson type catalysts. The fact that the 0:2:1 catalyst is readily desorbed from hectorite. which was the case for the HhCl(PPh3)3/Hect system as well (see Section III. B. 1). indicates that the complexes involved maintain their neutrality in the physisorbed state. The cationic complex [Hh(COD)(PPh3)2]X. where x = ClOu-. PF6’ or BFu'. is a known olefin hydrogenation catalyst.35 Schrock and Osborn attribute the reactivity of c this homogeneous catalyst to the presence of two species.35 The cationic dihydride. [HhH2(PPh3)2]+. which is formed following reduction of COD. is an active olefin hydrogenation catalyst but a poor olefin isomerization catalyst. This 95 complex is in pH dependent deprotonation equilibrium with a neutrally charged monohydride complex. HhH(PPh3)2. which is also an active hydrogenation catalyst but is also very active for olefin isomerization as well. [HhH2(FFh3)2]+ {—3 HhH(PPh3)2 + H+ As a result. as shown by the TO#'s in Table 7. the homo- geneous catalyst hydrogenates 1-hexene at a fair rate in the early stages of the reaction. but as the concentration of the isomerization product 2-hexene increases. the overall rate of olefin hydrogenation decreases because 2-hexene is reduced much more slowly than 1-hexene. Desorption of catalyst from Hh(COD)(PPh3)2+/Hect was observed visually at CT = 975. The desorbed species is probably the neutrally charged monohydride catalyst. From the rate data for Hh(CCD)(FFh3)2"’/Hect it might be inferred however. that the degree of monohydride formation in the mineral environment is less than that in homogeneous solution. High hydrogenation rates are maintained longer during the reaction with the supported catalyst. indicating that the extent of l-hexene isomerization is less and thus the concentration of the monohydride is lower. The generally acknowledged higher acidity of the mineral environment compared to methanol solution38 is most likely the major factor contributing to this effect. As expected based on the results presented in Section III. B. 1 for the phosphinated hectorite systems and in Section III. C. 2 for the 2:0:1 and 3:0:1 homogeneous 96 catalysts. both the 2:0:1/Hect and 3:0:1/Hect systems proved inactive as catalysts for olefin hydrogenation. IV. CONCLUSIONS AND RECOMMENDATIONS As described in the results and discussion section. this dissertation has shown that a positively charged ligand can be employed to produce an active cationic transition metal catalyst. The 1.1.1. P-P+BFu:PPh3:Hh. 'catalyst is active both in solution and when situated between the negatively charged sheets of the mica-like silicate hectorite. It is of considerable importance to note that. when in the mineral environment and under the reaction conditions employed here. the activity of the catalyst is increased. The 1:1:1 catalyst is a mixture of two or more cationic mixed phosphine ligand rhodium(I) chloride complexes which probably act in concert to generate highly active intermediates for olefin hydrogenation. The support appears to exert a positive effect on the catalytic activity of the 1.1.1 system. This effect may be attributed to the solution-like environment within the support and the ability of the large negatively charged silicate sheets to alter the stoichiometry and geometry of the complexes employed. These results have some significant implications. Cationic catalysts might be prepared in a simple. convenient manner. Judicious choice of appropriate ligands and 97 98 reaction conditions could produce complexes which might possess a number of different oxidation states. These compounds would have the potential for binding to a variety of'anionic supports. In particular. swelling. layered silicates seem ideal supports for immobilization of such species. Certain aspects of this dissertation deserve additional comment. Although the cationic ligand. P-P+BFu. was relatively easy to prepare and manipulate and it mimics the behavior of PPh3 up to a point. its large size and complexity relative to commonly used phosphine ligands probably preclude its use in other catalyst systems. A simpler. smaller cationic phosphine ligand comparable to PPh3 would find more general application since problems associated with ligand steric bulk and the need for mixed phosphine ligand systems would be minimized. Most of the known cationic phosphine ligands mentioned in Section I. D. would be no better than P-P+BFu as far as size is concerned. although the methyl substituent on the quaternized phosphorus in the ligand (PhZPCHZCHzPPhZCH3)+ is an improvement. The smaller ligands [P(CH20)3PCH3]BF,+52 50b and (PhZPCH OH NH H)X would be more suitable. although 2 2 2 the former may be too basic for many applications and in the latter the protonated amine suffers from pH restrictions and the ethylene bridge still allows ligand conformations which would crowd metal coordination sites. The neutral ligands (p-MeZNC6Hh)PPh2. (p-MecheHh)2PPh 99 and (p-MechéHu)3P should possess the same steric bulk as PPh3 and are known to mimic its behavior in certain catalytic 75 systems. Quaternization of one or more of the amine groups would produce cationic phosphine ligands capable of substitution for PPh3 in the preparation of a variety of transition metal complexes. However. these complexes should exhibit different catalytic reactivities than the PPh3 systems since one expects that the cationic phosphine ligands would be significantly poorer bases than PPh3. due to the strongly electron withdrawing trialkylammonium groups attached to the phenyl rings. The cationic ligand (Me2N+CH206Hu)PPh2 is as yet unknown. but it should possess electronic and steric properties that are similar to those of PPh3 and/or P(p-tolyl)3. (H3N+CH2C6Hh)3P is a known ligand.76 but it would only be useful in acidic media. The phosphinated hectorites employed in this study appeared to bind rhodium complexes. but these materials were not successful catalyst precursors presumably because of the bulkiness of the cationic ligand. Analogous phosphinated hectorites prepared with smaller cationic phosphine ligands. possibly at lower concentration within the intracrystal space. might well serve as catalyst supports. These materials might also find uses as molecular sieves and/or as metal ion or complex trapping agents. A simple method of phosphinated hectorite preparation might be found in the protonation of the amine groups of (p-Mechéflh)3P by the acid exchanged mineral. H+/Hect. 100 The surface catalyzed disproportionation of‘[HhCl(COE)2]é deserves further study. It would be of interest to determine the species produced from the reaction and establish a plausible mechanism. The chemistry associated with the preparation and utilization of silylated montmorillonite and hectorite should also be investigated. These materials may prove very useful as supports for the immobilization of moisture sensitive catalysts and may extend the uses of smeetites to systems whose reactivities are inhibited by the presence of protonated solvents and/or hydroxyl groups. The use of ligand functionalized silane coupling agents in place of (CH3)3Six in the silylation reaction might allow the preparation of dual purpose supported catalysts. It is feasible that two different catalysts could be supported on the same mineral. one within the interlayers and the other attached to edge sites ylg the silane coupling agent. In addition to the positively charged ligands discussed in this dissertation. there exists a number of other cationic and zwitterionic ligands of variable functionality which might be employed to synthesize cationic complexes of catalytic interest. Some examples of positively charged 7 nitrogen ligands are the amines. HZNCHZCH2N+H3.7 + 78 N(CH2CH2)3N H and N(CHCH) 21):"CH379 and the nitrile. +— 80 + 81 NCC(CHCH)2N CH3. An arsine is known. thAsCHZCHzAs thH. and a sulfonium ligand. MeBSI. has been reported recently.82 Zwitterionic carboxylate ligands such as (Me3N+CH2C02') 101 have been studied for some time for their biochemical interest.83 Organometallic ligands containing positive charge are also known. such as the cyclopentadienyl ligand CSHQPIPh3.8h the carbanion.(PhMe2P+CHZCH').85 the cyclo- octatetraenyl ligand 08H7CH2N+he3.86 and the allyl ligand Fh3F*CH(CH)20H.°7 Finally. the following list of complexes. which are known homogeneous catalysts. probably only hints at the number and variety of systems which might be rendered cationic through the judicial utilization of positively charged ligands in their preparation (see Table 8). 102 Table 8. Some Known Homogeneous Catalysts Potentially Suitable for Modification by Positively Charged Ligands* Complexes T1(CP)2(CO)2 MnCp(CO)2(PPh3) Fe(Ht)2dipy)2 Fe(CO)4(PPh )3 [Co(co)3LJ2 Co073-03H5)[F(0he)3j5 Ni(PPh3)3 Ni(CO)2(PPh3)2 NiClz(PEt3)2 Ni(COD)(PPh3)3 Ni(PPh3)u Ni(Et)(dipy)2 Mo(CO)5(PPh 21.01214 HhClIC0)L2 3) HhH(C0)L3 Rh6(°°)ie-nLn HhCln(N33) HhCln(NCR) PdC12(PPh3)2 Selected Uses o1 H2 Hz/CO olig. poly H2/00 Hz/Co. ket H2 ar H2 XPh/HCN olig. poly isom. olig olig dimer olig. poly Hz/CO Hz/CO. 01 H2 Hz/CO Hz/CO 01 H2 H31 H31 HOPh/NR . Type of Cationic Ligand Needed cyclopentadienyl cyclopentadienyl or phosphine amine phosphine phosphine phosphite phosphine phosphine phosphine phosphine phosphine amine phosphine phosphine phosphine phosphine phosphine amine nitrile phosphine Ed 103 Table 8. (cont'd). 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