Oxidatively induced reductive elimination in transition metal-catalyzed C–H functionalizations

Abstract

Significant advances in transition metal-catalyzed coupling reactions have provided novel and efficient procedures for synthetic and industrial chemistry, instigating exploration on the mechanistic details of the catalytic cycle. Among the mechanistic components of catalytic coupling reactions, reductive elimination constitutes a key bond-forming step for the product formation, thereby has been extensively studied to facilitate this process. Seminal studies revealed that oxidation of the metal center in certain post-transmetalation intermediates promotes the reductive elimination process, necessitating much milder conditions for the desired chemical bond formation. This phenomenon, called oxidatively-induced reductive elimination (ORE), has been known for a long time but only seldom proposed in catalytic coupling reactions. This dissertation deals with the high-valent pathway in catalytic C–H aryl- and methylation process using isoelectronic Cp$^*$Ir(III), Cp$^*$Rh(III), and (p-cymene)Ru(II) catalysts with a range of oxidation systems. After demonstrating that the ORE mechanism is commonly operative for the C–C bond formation from all three Ir, Rh, and Ru intermediate with conventional chemical oxidants, its application on the development of novel catalytic reactions will be showcased. We further demonstrated that in lieu of chemical oxidants, photocatalytic redox processes, and even internal metal-to-ligand charge transfer are also able to generate the high-valent intermediate to facilitate the C–C bond-forming reductive elimination under catalytic conditions.