Our density functional theory study reveals that the dehydrogenation of ethanol catalyzed by an aliphatic PNP pincer Ru complex,(PNP)Ru(H)CO {1Ru,PNP = bis[2-(diisopropylphosphino)-ethyl]amino},and its Fe analogue,(PNP)Fe(H)CO(1Fe),proceed via a self-promotion mechanism that features an ethanol molecule acting as a bridge to assist the transfer of a proton from ligand nitrogen to the metal center for the formation of H2.The calculated total free energy barrier of ethanol dehydrogenation catalyzed by 1Fe is only 22.1 kcal/mol,which is even 0.7 kcal/mol lower than the calculated total free energy barrier of the reaction catalyzed by 1Ru(Figure 1).Therefore,the potential of 1Fe as a low-cost and high-efficiency catalyst for the production of hydrogen from ethanol is promising.1 A recent experimental study of Beller and co-workers has confirmed 1Fe is an active catalyst for the dehydrogenation of methanol under mild condition.2 In addition to the finding of above self-promoted dehydrogenation mechanism for the aliphatic pincer complexes,the very different catalytic properties between the in ruthenium complexes with aromatic and aliphatic pincer ligands are analyzed based on our calculation results.