Evidence for an oxygen evolving iron-oxo-cerium intermediate in iron-catalysed water oxidation

The non-haem iron complex alpha-[Fe-II(CF3SO3)(2)(mcp)] (mcp = (N,N'-dimethyl-N,N'-bis (2-pyridylmethyl)-1,2-cis-diaminocyclohexane) reacts with Ce-IV to oxidize water to O-2, representing an iron-based functional model for the oxygen evolving complex of photosystem II. Here we trap an intermediate, characterized by cryospray ionization high resolution mass spectrometry and resonance Raman spectroscopy, and formulated as [(mcp)Fe-IV(O) (mu-O)Ce-IV(NO3)(3)](+), the first example of a well-characterized inner-sphere complex to be formed in cerium(IV)-mediated water oxidation. The identification of this reactive Fe-IV-O-Ce-IV adduct may open new pathways to validate mechanistic notions of an analogous Mn-V-O-Ca-II unit in the oxygen evolving complex that is responsible for carrying out the key O-O bond forming step.