Comprehensive Thermodynamic Characterization of the Metal−Hydrogen Bond in a Series of Cobalt-Hydride Complexes

TLDR: These measurements and the determinations of various electrochemical potentials were used to determine 11 of 12 possible homolytic and heterolytic solution Co-H bond dissociation free energies of [H(2)Co(dppe)(2)](+) and its monohydride derivatives.

Abstract: A detailed structural and thermodynamic study of a series of cobalt-hydride complexes is reported. This includes structural studies of [H2Co(dppe)2]+, HCo(dppe)2, [HCo(dppe)2(CH3CN)]+, and [Co(dppe)2(CH3CN)]2+, where dppe = bis(diphenylphosphino)ethane. Equilibrium measurements are reported for one hydride- and two proton-transfer reactions. These measurements and the determinations of various electrochemical potentials were used to determine 11 of 12 possible homolytic and heterolytic solution Co−H bond dissociation free energies of [H2Co(dppe)2]+ and its monohydride derivatives. These values provide a useful framework for understanding observed and potential reactions of these complexes. These reactions include the disproportionation of [HCo(dppe)2]+ to form [Co(dppe)2]+ and [H2Co(dppe)2]+, the reaction of [Co(dppe)2]+ with H2, the protonation and deprotonation reactions of the various hydride species, and the relative ability of the hydride complexes to act as hydride donors.