Ammonia Triborane: A New Synthesis, Structural Determinations, and Hydrolytic Hydrogen-Release Properties

Iodine oxidation of B(3)H(8)(-) in glyme solution to produce (glyme)B(3)H(7), followed by displacement of the coordinated glyme by reaction with anhydrous ammonia provides a safe and convenient preparation of ammonia triborane, NH(3)B(3)H(7) (1). X-ray crystallographic determinations and DFT computational studies of both NH(3)B(3)H(7) and the NH(3)B(3)H(7) x 18-crown-6 adduct demonstrate that while computations predict a symmetric single bridging-hydrogen conformation, NH(3)B(3)H(7) has a highly asymmetric structure in the solid-state that results from intermolecular N-H(+)...H(-)-B dihydrogen bonding interactions. Studies of its hydrolytic reactions have shown that upon the addition of acid or an appropriate transition metal catalyst, aqueous solutions of 1 rapidly release hydrogen, with 6.1 materials wt % H(2)-release being achieved from a 22.7 wt % aqueous solution of 1 at room temperature in the presence of 5 wt % Rh/Al(2)O(3) (1.1 mol% Rh). The rate of H(2)-release was controlled by both the catalyst loadings and temperature.