Transition metal complexes that catalyze oxygen formation from water: 1979–2010

The study of catalytic water oxidation continues to be one of the most active areas of research across many sub-disciplines of chemistry. From efforts toward developing artificial photosynthetic assemblies to the exploration of nanoscale materials to be used as a photoanode for splitting water, a detailed understanding of the mechanistic details of water oxidation in photosystem II (PSII) is paramount for the rational design of an artificial model. In addition, insight into the model's mechanism of molecular-level water-oxidation catalysis will provide us with a unique opportunity to elucidate the mechanistic pathways of water oxidation in the oxygen-evolving complex (OEC) of PSII.In this review, the proposed mechanisms, catalytic activities and reaction kinetics of catalytic water oxidation with transition metal complexes in homogeneous systems published from 1979 to 2010, with an emphasis on the last decade, are discussed. These metal complexes include mononuclear, dinuclear and multinuclear manganese, ruthenium, iridium, iron and cobalt complexes. Electrodeposited cobalt complexes are a type of heterogeneous water-oxidation catalyst; however, these complexes are discussed herein because they are topological analogs of the Mn cluster in the OEC. MVO species (M = Mn, Ru) as the key active species in homogeneous catalytic evolution of O2 are common feature in many catalysts, in which formation of the OO bond can be achieved either by intramolecular elimination of dioxygen from two MVO groups or by nucleophilic attack of OH− species on MVO groups. Another common feature appears from tetranuclear ruthenium complex 71, manganese complex 10 and cobalt complex, all of these cubane structural complexes have self-repair properties similar to OEC–protein complex in nature.

► MVO species (M = Mn, Ru) as the key active species in homogeneous catalytic evolution of O2 is one common feature.
► Formation of OO bond can be achieved by intramolecular elimination of dioxygen from two MVO groups.
► Formation of OO bond can be achieved by nucleophilic attack of OH− species on MVO groups.
► Cubane structural complexes 71, 10 and cobalt complex have self-repair properties similar to OEC–protein complex.