A new strategy to efficiently cleave and form C-H bonds using proton-coupled electron transfer.

Abstract

Oxidative activation and reductive formation of C-H bonds are crucial in many chemical, industrial, and biological processes. Reported here is a new strategy for these transformations, using a form of proton-coupled electron transfer (PCET): intermolecular electron transfer coupled to intramolecular proton transfer with an appropriately placed cofactor. In a fluorenyl-benzoate, the positioned carboxylate facilitates rapid cleavage of a benzylic C-H bond upon reaction with even weak 1<i>e</i>^- oxidants, for example, decamethylferrocenium. Mechanistic studies establish that the proton and electron transfer to disparate sites in a single concerted kinetic step, via multi-site concerted proton-electron transfer. This work represents a new elementary reaction step available to C-H bonds. This strategy is extended to reductive formation of C-H bonds in two systems. Molecular design considerations and possible utility in synthetic and enzymatic systems are discussed.