ABSTRACTSINGLE-SITE MOLYBDENUM(IV) MEDIATED BOND CLEAVAGE REACTIONSANDLIGAND PARAMETERIZATION USING A CHROMIUM(VI) PLATFORMByStephen Andrew DiFranco The following pages comprise various studies in the area of organometallic chemistry of the transition metals and may be separated into two main projects; exploration of novel molybdenum(IV) bispyrrolide complexes with implications toward the mechanism(s) of catalytic dinitrogen fixation, and electronic and steric parameterization of ligands using a chromium(VI) nitride complexes. Chapter 1 discusses a novel 2e− reduction the N-N bond in disubstuted hydrazines that proceeds via a Mo-hydrazido(1-) moetiy to produce a Mo(VI) nitride and a free secondary amine from N-N bond cleavage. Kinetic studies on this and an analogous Zr(IV) system are presented. The related N-O bond cleavage of o-benzyl hydrazine is also reported. Such single-site bond cleavage reactions may be operative in the enzymatic reduction of dinitrogen, and my find use in future catalytic systems toward the same end. Chapter 2 focuses on the reactivity of the same molybdenum(IV) bispyrrolide with alcohols, giving either mono or multiple substitutions resulting in Mo(IV) alkoxides, or radical C-O bond cleavage commensurate with Mo(VI) bisoxo and C-C bond formation. Additional reactivity and structural studies of molybdenum(IV) bispyrrolides are presented in Chapter 3. Chapter 4 presents the synthesis of 28 new chromium nitride complexes of the form NCr(NPri2)2X where X is a halide or anionic ligand bound through O, N or S. A method for using Spin Saturation Magnetization Transfer to measure the kinetics of diisopropylamide rotation is discussed. These barriers of rotation are indicative of the donor ability of the X ligand, and have been reported as the Ligand Donor Parameter (LDP) of each compound. Structural analysis is included of each compound, as it steric analysis using two different systems. Additionally, correlations to Hammett parameters, pKa's, 13C NMR data, electronic spectra, and the angular overlap model are presented. Chapter 5 explores similar NCr(NPri2)2X compounds where X is cyclopentadienyl and related compounds. Further substitution induces a hapticity shift in the bound Cp. Chapter 6 presents a new set of compounds based on the NCr(NPri2)2X platform where X is an organometallic ligand bound through carbon. Synthesis, structures, LDP's and steric analysis are presented. Chapter 7 discusses synthesis of cationic Cr(VI) nitridos of the form [NCr(NPri2)2L][A] where L is a neutral 2e− donor and A is a weakly coordinating anion. LDP's and a correction for anion effects are presented. Temperature dependent equilibrium in cation formation is reported. Structural and steric analysis of many of the compounds are included. Chapter 8 focuses on the synthesis and structure of a 3-ferrocenyl substituted pyrrolide ligand. Structural, steric and LDP analysis is discussed. In total a series of 58 ligands bound through O, N, P, S and C and halides have been parameterized via the LDP methodology. This list spans both neutral and anionic ligands. Crystal structures and steric analysis for many of these are included as to comprise a comprehensive map of ligation toward transition metals
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