In this computational study, the thermodynamics of H-2, proton, and hydride transfer from 13 ammonium borohydride and six phosphonium borohydride intramolecular and intermolecular frustrated Lewis pairs (FLPs) was probed to gain insight into whether intramolecular or intermolecular amine-containing FLPs are preferred to phosphine-containing FLPs in FLP-catalyzed hydrogenation reactions. H-2, hydride, and proton transfer from intramolecular ammonium borohydrides was, on average, 2.6 kcal/mol, 0.7 kcal/mol, and about 3.8 pK(a) units, respectively, less likely than from intramolecular phosphonium borohydrides. Using the thermodynamic quantities for H-2, hydride, and proton transfer to eight probe substrates, intramolecular phosphonium borohydrides were found to be thermodynamically preferred to intramolecular ammonium borohydrides in catalytic hydrogenation reactions.