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

A detailed structural and thermodynamic study of a series of cobalt-hydride complexes is reported. This includes structural studies of H(2)Co(dppe)(2)(+), HCo(dppe)(2), HCo(dppe)(2)(CH(3)CN)(+), and Co(dppe)(2)(CH(3)CN)(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 H(2)Co(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 H(2)Co(dppe)(2)(+), the reaction of Co(dppe)(2)(+) with H(2), the protonation and deprotonation reactions of the various hydride species, and the relative ability of the hydride complexes to act as hydride donors.