Uncatalyzed Transfer Hydrogenation and Transfer Hydrogenolysis: Two Novel Types of Hydrogen‐Transfer Reactions

Abstract

Abstract Uncatalyzed transfer hydrogenations are H 2 ‐transfer reactions in which donors that contain weakly bound hydrogen atoms undergo an H‐atom transfer (retrodisproportionation) onto an acceptor containing unsaturated bonds such as CC, CO, CN, NN, NO. Transfer hydrogenolyses are reactions in which σ bonds are cleaved upon additon of H 2 . These hydrogenations are terminated by H, transfer; they do not follow a radical‐chain mechanism. The initial steps of both types of reactions, H‐atom transfer, complement the bimolecular formation of 1,4‐diradicals from alkenes or heteroalkenes within the scope of bimolecular radical formation (Molecule‐Induced Radical Formation, MIRF). The title reactions play an important role in coal liquefaction, aromatization reactions with nitroarenes or quinones, and possibly biochemical dehydrogenations. This review focuses on mechanistic studies, structure–reactivity relationships, and current applications of these reactions.