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The mechanism of tandem dimethylamine-borane (NHMe2BH3, DMAB) dehydrogenation and alkene hydrogenation catalyzed by [Pd(NHC)(PMe3)] are investigated by density functional theory (DFT) calculations [NHC = N,N′-bis(2,6-diisopropylphenyl) imidazole-2-ylidene]. Four possible DMAB dehydrogenation mechanisms have been carefully investigated involving concerted B H/N H activation, sequential B H/N H activation, sequential N H/B H activation, and proton transfer mechanism. DFT studies show that the N H proton transfers to ligated carbene carbon and sequential C H/B H activation is the most kinetically favorable pathway with the lowest activation barrier of 23.8 kcal/mol. For hydrogenation, it was found that a trans-dihydride Pd(II) complex, [Pd(H)2(NHC)(PMe3)], formed in the dehydrogenation process, serves as an effective catalyst for reduction of trans-stilbene.

A quantum-chemical mechanistic investigation using density functional theory (DFT) on ammonia-borane dehydrogenation catalyzed by a series of iron bis(phosphinite) pincer complexes is reported. A metal-ligand cooperation mechanism has been proposed, in which the hydrogen atom of B H moves to metal Fe and proton of N H transfers to pincer ipso carbon simultaneously with the lowest activation barriers. DFT calculations and natural bond orbital (NBO) charge analysis suggest that Fe POCOP complex with an electron-donating MeO group at the para position to the ipso carbon exhibits the highest catalytic activity. A plausible explanation of the observed catalytic activities is also given.