| Abstract
| - High-level electronic structure calculations have been used to predict the thermodynamic stability of ammoniatriborane B3H7NH3 and the molecular mechanism of H2 elimination from various isomeric forms in the gasphase. Geometries of stationary points were optimized at the second-order perturbation theory MP2 level,and total energies were computed at the coupled-cluster CCSD(T) theory with the aug-cc-pVnZ (n = D, T,Q) basis sets and extrapolated to the complete basis set limit. Heats of formation for the structures consideredin the gas phase were evaluated at both 0 and 298 K. The lowest-energy process for H2 release from the moststable isomer of B3H7NH3 is a 1,3-elimination characterized by an energy barrier of 28.9 kcal/mol. Althoughthe barrier height for H2 release from B3H7NH3 is slightly smaller than the B−N bond cleavage energy of30.7 kcal/mol yielding B3H7 + NH3, the calculated rate coefficients predict that bond cleavage is faster thanH2 release by 3 orders of magnitude at 298 K and 1 atm. We predict the heat of formation for the most stableisomer of B3H7 to be ΔHf (0 K) = 37.1 ± 0.8 kcal/mol and ΔHf (298 K) = 32.5 ± 0.8 kcal/mol, and for themost stable isomer of B3H7NH3 to be ΔHf (0 K) = 0.4 ± 1.0 kcal/mol and ΔHf (298 K) = −7.1 ± 1.0kcal/mol.
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