Oxidations of O-H and C-H Bonds: From Hydrogen Atom Transfers to Proton-Coupled Electron Transfer
Professor Jim Mayer
Department of Chemistry
University of Washington
Hydrogen atom transfer is a fundamental chemical process, involved in a wide variety of industrial, biochemical, and environmental processes. Many transition metal complexes and active sites use this as a key step in their oxidations of C–H, O–H, and other s-bonds. Examples to be described include oxidations of alkylaromatic compounds and hydroxylamines by ruthenium-oxo and iron-imidazoline complexes. In general, these reactions occur with concerted proton transfer to a ligand and electron transfer to the metal center. Rate constants for such hydrogen atom transfer reactions can, in many cases, be predicted by Marcus Theory, using the driving force and intrinsic barriers. This analysis provides a bridge between organic and transition-metal H-atom transfer processes. The second section of the presentation will describe oxidations of phenols with an pendent base, in which the electron and proton become separated in the phenoxyl radical products. These are emblematic of another class of proton-coupled electron transfer reactions.