LAUSR

Abstract The paper presents a brief overview of the role of metal hydride complexes in understanding the dynamics of hydrogen generation in homogeneous water reduction catalysts. In addition, the kinetics of protonation of [Os(phen)2(CO)(H)]+ and the one-electron reduced form of the complex, [Os(phen)(phen−)(CO)(H)], in acetonitrile solution were examined. The monocationic complex reacted with tosylic acid to form a distinct intermediate species which was found to be a dihydrogen complex; this went on to produce hydrogen and the solvento complex. The one-electron reduced complex was prepared by reduction of the photoexcited monocationic complex with the sacrificial donor BIH. Protonation of the reduced complex by tosylic acid occurred with a rate constant approximately 100 million times larger. The results are used to address possible mechanistic pathways of existing homogeneous catalysts.