Molybdenum Catalyzed Ammonia Borane Dehydrogenation: Oxidation State Specific Mechanisms

Though numerous catalysts for the dehydro­gen­ation of ammonia borane (AB) are known, those that release >2 equiv of H₂ are uncommon. Herein, we report the synthesis of Mo complexes supported by a <i>para</i>-ter­phenyl diphosphine ligand, <b>1</b>, displaying metal–arene interactions. Both a Mo⁰ N₂ complex, <b>5</b>, and a Mo^II bis­(acetonitrile) complex, <b>4</b>, exhibit high levels of AB de­hy­dro­genation, releasing over 2.0 equiv of H₂. The reaction rate, extent of dehydrogenation, and reaction mechanism vary as a function of the precatalyst oxidation state. Several Mo hydrides (Mo^II­(H)₂, [Mo^II(H)]⁺, and [Mo^IV(H)₃]⁺) relevant to AB chemistry were characterized