Molybdenum catalyzed ammonia borane dehydrgenation

Ammonia borane (AB, NH_3BH_3) and substituted amine borane adducts (NR_3BH_3) have received considerable interest as both promising modes of chem. hydrogen storage (up to 19.6 % for AB) and as precursors to inorg. B-N-contg. materials. Though numerous methods for the dehydrocoupling of AB are known, homogeneous transition metal catalysis provides promise for controlling the rate and extent of dehydrogenation, as well as defining the microstructure of the generated inorg. polymer. Though numerous catalysts for this process are known, those that release greater than 2 equiv (equiv.) of hydrogen (H2) are rare. We report the synthesis of low-valent molybdenum complexes supported by a para-terphenyl diphosphine (P2) ligand displaying metal-arene interactions. Both the Mo°c dinitrogen complex, P2Mo(N_2) (1), and the MoII bisacetonitrile complex, [P2Mo(MeCN)_2]^2+ (2), exhibit high levels of dehydrogenation when treated with AB, each releasing over 2.5 equiv. of H2. There is a marked difference in reaction rate and stability, with 2 proving to be both more active and robust. Structural and reactivity studies of species relevant to catalysis will be discussed