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.