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-2ylidene]. 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. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.