The novel hydrogen dense dinuclear cobalt hydride

We have been interested in preparing new soluble hydrogen rich complexes of the transition metals since our original synthesis of [FeH6][MgBr(THF)2]4. These compounds are sought because they are intermediates in novel routes to metallic materials and also new hydrogenation catalysts. The search for the soluble homoleptic hydride of cobalt entailed a reaction of cobalt(II) bromide and six equivalents of phenylmagnesium bromide in THF solution under an atmosphere of hydrogen for 24 hours at temperatures between -70 and 23 °C. A striking difference in the cobalt vs. iron reaction has been the amount of biphenyl produced as a by-product (50% vs. 9% based on metal); nevertheless, an isolable yellow complex hydride precipitated. Analysis by 1H NMR and IR of this molecule and its D-labeled analogue has clearly demonstrated the presence of the Co-H bond. The solid state monomeric species Mg2CoH5 has precedence. Unexpectedly, XAFS and XANES analysis reveals a novel dinuclear cobalt hydride complex with three primary absorbers [n = 1, Co-Co, r = 2.4529(2); n = 4, Co-H, r= 1.544(7); n = 2, Co-H, r = 1.822(7)]. DFT studies combined with multiple elemental analyses have been undertaken to probe the electronic structure and to arrive at the correct formulation