Manganese and ruthenium complexes are perhaps the most well-known molecular systems for water oxidation, but relatively new efforts have targeted development of iridium-, iron-, cobalt-, and copper-based systems. In the proposed mechanism of oxygen evolution oxone first binds to the (III,IV) dimer. Because there are two manganese centers, one Mn(III) and one Mn(IV), there are already two paths here. When oxone binds to Mn(IV), there can be no oxidation since a two-electron oxidation would give a Mn(VI), which is inaccessible in this ligand environment even with the high-potential oxone. When it binds to the Mn(III), however, productive chemistry does result. McKenzie and co-workers studied a dinuclear manganese complex as a catalyst for water oxidation driven by tert-butyl hydroperoxide. A number of other manganese compounds have recently been reported by Anderlund and others to function as catalysts for water oxidation, driven by oxone or cerium(IV). Due to the ability of the analogous metal oxides to catalyze water oxidation, catalysts of manganese, iridium, and cobalt have recently attracted major scrutiny in a search for evidence of true molecular reactivity.
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