The Carboxylate Ligand as an Oxide Relay in Catalytic Water Oxidation.

• Carboxylate groups have diverse functionality in ligands of transiton metal catalysts. Here we present a conceptuallydifferent function of the carboxylates – the oxide relay. It functions by providing an intramolecular nucleophilic oxygen close tothe oxo group to facilitate O-O bond formation, and at a later stage a remote electrophilic center to facilitate OH- nucleophilic attack.EVB-MD models were generated for key bond forming steps, diffusion coefficients and binding free energies from potentialof mean force estimations were calculated from MD simulations, activation free energies of chemical steps were calculated usingdensity functional theory. The catalyst studied is the extremely active Ru(tda)(py)2 water oxidation catalyst. The combination ofsimulation methods allowed for estimation of the turnover frequencies, which were within one order of magnitude from the experimentalresults at different pH values. From the calculated reaction rates we find that at low pH the OH- anion nucleophilic attack isthe rate-limiting step, which changes at high pH to the O-O bond formation step. Both steps are extremely rapid and key to theefficiency is the oxide relay functionality of a pendant carboxylate group. The functionality was discovered for a ruthenium catalyst,but since there is nothing in the mechanism restricting it to this metal, the oxide relay functionality could open new ways todesign the next generation water oxidation catalysts with improved activity.

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