Water oxidation catalyzed by dimeric μ-oxo bridged ruthenium diimine complexes

Dimeric μ-oxo ions such as cis,cis-[(bpy)2Ru(OH2)]2O4+, its congeners containing ring-substituted bipryidine ligands, and related structures have long been known to efficiently catalyze water oxidation by strong chemical oxidants and at electrode surfaces. However, despite considerable effort, the goal of identifying the underlying molecular mechanisms has not yet been realized. In this contribution issues concerning the reactivity of these catalysts are reviewed from the perspective of recent research findings, which have led to considerable clarification of the reaction pathways. Alternative postulated molecular mechanisms are also discussed within the framework of general principles governing the reactivity of group 8 polypyridyl complexes.