PH-DEPENDENT METAL-BASED REDOX COUPLES AS MODELS FOR PROTON-COUPLED ELECTRON-TRANSFER REACTIONS

An overview of proton-coupled electron transfer in transition metal-li gand systems known to exhibit pH-dependent metal-based redox potential s is presented. The systems of interest can be thought of as MLHm comp lexes, where M is a redox-active metal and LHm is a ligand in the inne r-coordination sphere containing at least one ionizable hydrogen. The use of pH-dependent redox potentials to determine proton-coupled elect ron transfer reactions is described, along with some important factors for designing and studying complexes that exhibit this behavior. This chemistry is illustrated by a survey of the common transition metal-l igand systems known to give pH-dependent redox potentials indicative o f proton-coupled electron transfer. (C) 1998 Elsevier Science S.A. All rights reserved.