Session: Inorganic Catalysts:

A series of Ca-Mn clusters, with the ligand 2-pyridinemethoxide (Py-CH₂O), have been prepared with varying degrees of topological similarity to the CaMn₄ oxygen evolving complex (OEC) of photosystem II. Through variation of reagent stoichiometry, Mn₄, CaMn₃, CaMn₅, Ca₂Mn₄, and Ca₄Mn₃ clusters are prepared via self-assembled precursor fragments and fully characterized. All products feature a hemicubane motif (a heterocubane structure minus one corner metal ion) with Mn or Ca atoms bridged by oxygen, while containing water-accessible metal coordination sites. These clusters are able to activate water as a substrate in the oxidative degradation of stable propylene carbonate into CO₂. The propensity of these clusters to activate water in this oxidation reaction is correlated with increasing topological similarity to the OEC. For instance, the CaMn₃(PyCH₂O)₆(N(SiMe₃)₂)₂(THF) cluster is most similar in topology to the OEC (having identical core atom arrangements but for the absence of one Mn ion) and lowers the onset potential of the oxidation by approximately 700 mV.

Michael Gau

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