Elucidating the Mechanism and Intermediates of Nitrogen-Atom Transfer From Diruthenium Carboxylates

Abstract

Direct oxidation of hydrocarbon substrates to provide value added products (e.g., amines or alcohols) remains a challenge due to the strength and kinetic inertness of unactivated C–H bonds. Substrate pre-functionalization, for example by radical halogenation, followed by functional group interconversion is often necessary to access target products. Transition metal-catalyzed C–H functionalization provides an alternative strategy to overcome the kinetic barriers to C–H functionalization. Specifically, the use of metal-ligand multiply bound species (i.e., M=E or M≡E) has found use in both enzymes (e.g., cytochrome P450 and methane monooxygenase) as well as in purely synthetic systems (E = O, N, NR). Diruthenium paddlewheel (or lantern) nitride complexes (i.e., (Ru2X4)≡N) can engage in nitrogen-atom transfer (NAT) chemistry to furnish amine products, and confinement of these nitrides in porous media, such as metal-organic frameworks (i.e., Ru-HKUST-1) has enabled intermolecular amination of simple benzylic substratesa. This dissertation will present investigations of the mechanism of NAT from Ru2(O2CR)4X systems. Particular attention is given to the synthesis of intermediates implicated in a hypothetical NAT catalytic cycle and investigation of the stoichiometric reactivity of these compounds to develop these systems as platforms for NAT catalysis. Chapter I surveys the field of transition metal nitrides which have been employed for NAT to organic small molecules. Chapter II presents a combined theoretical and experimental investigation of the mechanism of NAT from Ru2(O2CR)4N to benzylic C–H bonds. Chapters III and IV present synthesis and characterization of intermediates relevant to NAT from Ru2(O2CR)4X. Chapter V will conclude the dissertation with a perspective on the future directions of the Ru2(O2CR)4X system for NAT.