EH3 (E=N, P, As) and H2 activation with N-heterocyclic silylene and germylene homologues

DFT calculations have been used to probe the mechanism of the addition reaction of group 15 hydrides EH3 (E=N, P, As) and H2 to a N-heterocyclic silylene and its germylene homologue. Nitrogen lone pair donation into the vacant p-orbital of Si and Ge is the first step of ammonia activation, whereas silylene and germylene behave as nucleophiles toward dihydrogen, phosphane, and arsane. Formation of 1,4-addition products is kinetically favoured in all cases. In excess ammonia, the assistance of a second molecule drastically lowers the 1,1-addition energy barriers, enabling formation of 1,1-addition products. The participation of a second molecule in the P-H bond activation of phosphane also lowers the 1,1-addition energy barriers, but not enough to cause inversion.