Abstract
A key step in dioxygen evolution during photosynthesis is the oxidative generation of the O-O bond from water by a manganese cluster consisting of M 2 (μ-O) 2 units (where M is manganese). The reverse reaction, reductive cleavage of the dioxygen O-O bond, is performed at a variety of dicopper and di-iron active sites in enzymes that catalyze important organic oxidations. Both processes can be envisioned to involve the interconversion of dimetal-dioxygen adducts, M 2 (O 2 ), and isomers having M 2 (μ-O) 2 cores. The viability of this notion has been demonstrated by the identification of an equilibrium between synthetic complexes having [Cu 2 (μ-η 2 :η 2 -O 2 )] 2+ and [Cu 2 (μ-O) 2 ] 2+ cores through kinetic, spectroscopic, and crystallographic studies.