Cobalt catalyzed hydrogen evolution and formic acid dehydrogenation

Abstract

A Co^I-triphos complex (triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane) reacts at room temp. with ptoulenesulfonic acid monohydrate in acetonitrile to generate hydrogen (0.5 equiv) and Co^(II) with a driving force of just 30 meV/Co. Protonation of Co^I produces a transient Co^(III)-H complex that has been characterized by NMR spectroscopy. The Co^(III)-H intermediate decays by second-order kinetics with an inverse dependence on acid concn. Anal. of the kinetics suggests that Co^(III)-H produces hydrogen by a dominant heterolytic channel in which a highly reactive Co^(II)-H transient is generated by Co^I redn. of Co^(III)-H. The Co^I-triphos complex also reacts with excess formic acid to produce H_2 and CO_2. The mechanism of this transformation has been probed electrochem. and in studies of the gas evolution kinetics.