A High-Valent Metal-Oxo Species Produced by Photoinduced One-Electron, Two-Proton Transfer Reactivity

Described herein is a photochemical approach to the generation of a high-valent metal-oxo species that utilizes a chromophore or "sensitizer", a semiconducting electron acceptor, and a redox buffer that poises a catalyst's initial protonation and oxidation state. The photoexcited sensitizer injects an electron into the semiconductor and then oxidizes the catalyst whose reactivity occurs in kinetic competition with back electron transfer. Core-shell SnO₂/TiO₂ semiconductor nanocrystallites inhibited charge recombination relative to TiO₂ acceptors. With low sensitizer-catalyst surface coverages, a novel trapping process is exploited that enables catalysis reactivity to be quantified on time scales ranging from nanoseconds to minutes. A proof-of-principle example provides the demonstration of a light-initiated, (1e^-, 2H⁺)-transfer reaction, with an inverse isotope effect of k_H/k_D = 0.63, to generate a Ru(IV) oxo species.