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Competitive Oxygen-18 Kinetic Isotope Effects Expose O–O Bond Formation in Water Oxidation Catalysis by Monomeric and Dimeric Ruthenium Complexes

Angeles-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 (doi:10.1039/c3sc51919h).

Competitive oxygen kinetic isotope effects (18O KIEs) on water oxidation initiated by ruthenium oxo (Ru=O) complexes are examined here as a means to formulate mechanisms of O–O bond formation, which is a critical step in the production of "solar hydrogen". The kinetics of three structurally related catalysts are investigated to complement the measurement and computation of 18O KIEs, derived from the analysis of O2 relative to natural abundance H2O under single and multi-turnover conditions. The findings reported here support and extend mechanistic proposals from 18O tracer studies conducted exclusively under non-catalytic conditions. It is also shown how Density Functional Theory calculations performed in tandem with experiments can constrain mechanisms of catalytic water oxidation and help discriminate between them.