Mechanistic investigations of cobalt-catalyzed hydrogen evolution

Abstract

Natural photosynthesis uses sunlight to drive the conversion of energy-poor mols. (H_2O, CO_2) to energy-rich ones (O_2, CH_2O_n). Many scientists are actively engaged in developing efficient artificial photosynthetic systems that split water into H_2 and O_2. Solar fuels prodn. involves three basic components: light absorption; charge transport; and multielectron redox catalysis. High on the list of challenges is the discovery of mols. that efficiently catalyze the redn. of protons to H_2. We have investigated the mechanisms of two types of cobalt hydrogen evolution catalysts: Co^(II)-diglyoxime and Co^I-(1,1,1-tris(diphenylphosphinomethyl) ethane) complexes. Time resolved spectroscopic measurements have provided crit. insights into the kinetics of H_2 prodn. In both cases, protonation of Co^I produces a Co^(III)-H complex. Redn. of Co^(III)-H by Co^I produces a Co^(II)-H transient that reacts rapidly with proton donors to produce H_2.