Redox-innocent metal ions have been found to play critical roles in various synthetic transformations as well as biocatalytic processes. One prominent example is the need of a Ca2+ ion within the oxygen evolving complex (OEC) that is involved in biological water oxidation during photosynthesis. It is still not fully understood what makes the Ca2+ ion an indispensable cofactor in the dioxygen production, yet it has been shown that Ca2+-depleted OEC clusters are not able to generate dioxygen. Replacing the Ca2+ ion with a Sr2+ ion can lead to partial dioxygen generation, but other metal ions lead to an inactivity. Another aspect of understanding how the OEC works is to gain structural as well as spectroscopic insights into the oxidized forms of the OEC cluster. It has been proposed that a high-valent Mn center are involved in the oxidized form of the OEC. To examine the role for high valent Mn centers and a Ca2+ ion in the OEC, we have developed heterobimetallic complexes with MnIII—(μ-OH)—MII (where MII = Mg, Ca and Sr) cores using a multi-functional phosphinic amido-based tripodal ligand; this ligand controls the assembly of the MnIII—(μ-OH)—MII core and controls the secondary coordination sphere around the Mn center with intramolecular hydrogen bonds. The presentation will describe the preparation and characterization of these heterobimetallic constructs and their oxidized forms, including those with high-valent MnIV—(μ-O)—MII and MnIV—(μ-OH)—MII cores. Their relationships to species found within the OEC will be discussed.

Accessing high-valent manganese centers in MnIII-(µ-OH)-MII (MII = Mg, Ca, Sr) heterobimetallic complexes

ACS Spring 2022

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