Experimental and Theoretical Studies of the Potential Interconversion of the Amine-Borane iPr2NH•BH(C6F5)2 and the Aminoborane iPr2N=B(C6F5)2 Involving Hydrogen Loss and Uptake

The amineborane adduct iPr2NH center dot BH(C6F5)2 (1) and the aminoborane iPr2N=B(C6F5)2 (2) have been prepared and crystallographically characterised. Interconversion between the two compounds has been attempted using thermal and transition-metal-catalysed dehydrogenation and hydrogenation protocols and the overall reaction thermodynamics were probed by computational methods. Thermal dehydrogenation of 1 was found to yield 2, together with uncharacterised by-products. Treatment of 1 with the carbene 1,3-di-tert-butyl-4,5-dihydroimidazol-2-ylidene (3) under ambient conditions did not lead to the elimination of hydrogen, but instead to the loss of C6F5H to afford iPr2N=B(H)C6F5 (4). Attempts to hydrogenate aminoborane 2 were unsuccessful with no reaction observed either thermally or in the presence of transition-metal catalysts. A computational study of the interconversion between compounds 1 and 2 indicated a thermodynamically unfavourable hydrogenation reaction, which was inverse to that demonstrated for the analogous phosphaneborane/phosphanylborane pair, iPr2PH center dot BH(C(6)F(5))(2) (5) and iPr2PB(C6F5)2 (6). The contrasting reactivity was attributed to the different N-B and pi-B p-bond strengths in 2 and 6, respectively.