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

Iodine oxidation of B3H8− in glyme solution to produce (glyme)B3H7, followed by displacement of the coordinated glyme by reaction with anhydrous ammonia provides a safe and convenient preparation of ammonia triborane, NH3B3H7 (1). X-ray crystallographic determinations and DFT computational studies of both NH3B3H7 and the NH3B3H7·18-crown-6 adduct demonstrate that while computations predict a symmetric single bridging-hydrogen conformation, NH3B3H7 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 % H2-release being achieved from a 22.7 wt % aqueous solution of 1 at room temperature in the presence of 5 wt % Rh/Al2O3 (1.1 mol% Rh). The rate of H2-release was controlled by both the catalyst loadings and temperature.