The H 2-hydrogenation of ketones catalysed by ruthenium(II) complexes: A density functional theory study

Abstract

The catalytic cycle for the H 2-hydrogenation of ketones catalysed by Ru(diphosphine)(diamine) hydride complexes is studied at Density Functional Theory level. A model reaction is tested against a set of exchange–correlation density functionals: PBE, BLYP, B3LYP, B97-2 and BB1K. All methods agree in predicting the forward hydrogen transfer acetone/ i-Propyl alcohol reaction via the metal–ligand bifunctional mechanism to have a low energy barrier (⩽4 kcal/mol). The DFT results also agree with MP2 calculations. The analysis of the transition state structure involved in the hydrogen transfer via the metal–ligand bifunctional mechanism shows that the internuclear distances intimately involved in the reaction are sensitive to the density functional and the basis set employed, particularly the (Ru–)H ⋯ C( O) distance, which could be taken as the “pseudo” reaction coordinate. The PBE, BLYP, B3LYP, B97-2 and BB1K functionals have also been used to characterise the transition state involved in the H 2-splitting at the Ru 16-electron complex, which regenerates the trans-Ru(H) 2(PH 3) 2(en) catalyst. All DFT methods confirm the heterolytic nature of the dihydrogen splitting transition state and predict the H 2-splitting reaction to have higher activation energy.