The sun is the most abundant source of renewable energy available to us, but converting the light energy it produces into a storable, portable form remains a significant challenge. Organic ruthenium complexes have shown high efficacy for facilitating the oxidation of water into O2 and H2 gasses when a current is applied, making them promising materials for the development of artificial photosynthetic devices. We here report our work on rationally optimizing two existing water oxidation catalysts (WOCs) by using theory to predict and explain the effect that substitutions on the ligand systems might have in promoting higher catalytic efficiency. The efficiencies of WOCs Ru-Hbpp and Ru(tpy)(pynp) have been studied previously using the M06 suite of density functionals, and mechanistic pathways have been proposed.1,2 Building on these results, in the case of Ru-Hbpp we have tested the effects of substituting electron donating and withdrawing groups (–OCH3 and –NO2) near one of the Ru centers, in order to determine whether the removal of electron density from the metal might lower the energy of the rate-determining transition state: displacement of an O2 ligand by H2O. Theory predicts – and experiment confirms – that the electron withdrawing substituent decreases the rate of oxygen evolution, while the electron donating group has relatively little effect on the reaction rate. For Ru(tpy)(pynp), we have investigated the effects of replacing a naphthyridine with a quinoline moiety in the ligand system. This substitution, which amounts to replacing N in an N-heterocycle with CH, affects the catalytic efficiency of the complex, as well as allowing it to undergo reversible distal to proximal photoisomerization. 1Angeles-Boza, A.M.; Ertem, M.Z.; Sarma, R.; Ibañez, C.H.; Maji, S.; Llobet, A.; Cramer, C.J.; Roth, J.P. Chem. Sci. 2014, 5, 1141 2Hirahara, M.; Ertem, M.Z.; Komi, M.; Yamazaki, H.; Cramer, C.J.; Yagi, M. Inorg. Chem. 2013, 52, 6354

Theoretical prediction of the effects of substitution on the efficacies of ruthenium water oxidation catalysts

249th National Meeting (2015)

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