DFT studies of cobalt hydride intermediate on cobaloxime-catalyzed H2 evolution pathways

Chemical, electrochemical, and photochemical methods all had been utilized to explore proton reduction catalysis by cobaloxime complexes. It was postulated in these studies that the initial step toward making H2 was protonation of CoI to form a CoIII hydride intermediate. However, in the following steps, different results from electrochemical studies had led to both monometallic and bimetallic pathways. In this article, theoretical computation method (BP86/6-31G*) was firstly performed on possible cobalt hydride intermediates involved in the reactive pathway of cobaloxime-catalyzed H2 evolution. The monometallic pathway B was excluded, both monometallic pathway A and bimetallic pathway were the possible process. However, the Gibbs free energy change for generation of H2 following monometallic pathway A was much more negative than that following bimetallic pathway. The calculation on monometallic pathway A indicated that the main driving force of the reaction (i) came from the step of the reduction of 11. The proton transfer steps were also studied in detail. The protonation of cobalt hydride intermediates could directly happen on the dimethylglyoximate part. All the results refer to gas-phase calculations, not considering the solution. (c) 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011