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.

Electrocatalytic water activation by synthetic topological analogs of the oxygen evolving complex of photosystem II in oxidation of stable propylene carbonate

ACS Spring Meeting 2021

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