A Self-Promotion Mechanism for Efficient Dehydrogenation of Ethanol Catalyzed by Pincer Ruthenium and Iron Complexes: Aliphatic versus Aromatic Ligands

摘要

A density functional theory study reveals that the dehydrogenation of ethanol catalyzed by an aliphatic PNP pincer ruthenium complex, (PNP)Ru(H)CO {1Ru, PNP = bis[2-(diisopropylphosphino)ethyl]amino}, proceeds via a self-promoted 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 very different catalytic properties between the aromatic and aliphatic pincer ligand in ruthenium complexes are analyzed. The potential of an iron analogue of 1Ru, (PNP)Fe(H)CO (1Fe), as a catalyst for the dehydrogenation of ethanol was evaluated computationally. 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. Therefore, the potential of 1Fe as a low-cost and highefficiency catalyst for the production of hydrogen from ethanol is promising.