Forty years on - Covalent hydration of transition metal complexes revisited

The hypothesis that the reactivity, and in particular the kinetic behavior, of complexes of classical diimine ligands based on pyridine donors could be reinterpreted, in terms of reactivity at the ligand rather than the metal center was proposed some forty years ago by the Gillard group in Cardiff. The model received considerable resistance from the traditional inorganic chemistry community and has not received great attention in the past twenty years. This review surveys the modern evidence that has accrued, which indicates that the mechanistic proposals have fundamental merit, are indeed operative under extreme reaction conditions and may be of great relevance to the current big challenges associated with solar energy conversion and water splitting. (C) 2015 Elsevier Ltd. All rights reserved.