AB-INITIO MO AND MM STUDY ON THE NATURE OF [RU(P-P)2H-3]+ (P-P = DPPB, DIOP, DPMB, DPPE) COMPLEXES

A theoretical study has been carried out on [Ru(P-P)2''H3'']+ (P-P = dppb, diop, dpmb, dppe) complexes with the goal of clarifying the wide differences observed in their experimental NMR spectra. Electronic effects are evaluated through ab initio molecular orbital calculations at the MP2 and MP4 levels on the [Ru(PH3)4''H3'']+ model, while steric effects are quantified through molecular mechanics calculations on the [Ru(P-P)2] (P-P = dppb, diop, dpmb, dppe) model. The results suggest that the dominant species in solution are six-coordinate dihydrogen hydride [Ru(P-P)2H(H2)]+ complexes. Two different isomers of this complex seem possible, an octahedral trans species and a very distorted cis species, their relative energies depending on the particular diphosphine ligand. A trihydride complex is also found to play a substantial role as an intermediate in [Ru(diop)2''H3'']+.