Catalysis of Proton Reduction by a [BO_4]-Bridged Dicobalt Glyoxime

We report the preparation of a dicobalt compound with two singly proton-bridged cobaloxime units linked by a central [BO_4] bridge. Reaction of a doubly proton-bridged cobaloxime complex with trimethyl borate afforded the compound in good yield. Single-crystal X-ray diffraction studies confirmed the bridging nature of the [BO_4] moiety. Using electrochemical methods, the dicobalt complex was found to be an electrocatalyst for proton reduction in acetonitrile solution. Notably, the overpotential for proton reduction (954 mV) was found to be higher than in the cases of two analogous single-site cobalt glyoximes under virtually identical conditions

Cobalt catalyzed hydrogen evolution and formic acid dehydrogenation

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

Catalysis of Proton Reduction by a [BO₄]‑Bridged Dicobalt Glyoxime

We report the preparation of a dicobalt compound with two singly proton-bridged cobaloxime units linked by a central [BO₄] bridge. Reaction of a doubly proton-bridged cobaloxime complex with trimethyl borate afforded the compound in good yield. Single-crystal X-ray diffraction studies confirmed the bridging nature of the [BO₄] moiety. Using electrochemical methods, the dicobalt complex was found to be an electrocatalyst for proton reduction in acetonitrile solution. Notably, the overpotential for proton reduction (954 mV) was found to be higher than in the cases of two analogous single-site cobalt glyoximes under virtually identical conditions