Dihydrogen-bond-promoted catalysis:: Catalytic hydration of nitriles with the indenylruthenium hydride complex (η5-C9H7)Ru(dppm)H (dppm = bis(diphenylphosphino)methane)

The indenylruthenium hydride complex (eta(5)-C9H7)Ru(dppm)H was found to be active in catalyzing the hydration of nitriles to amides. The chloro analogue (eta(5)-C9H7)Ru(dppm)Cl was, however, found to be inactive. Density functional theory calculations at the B3LYP level provide explanations for the effectiveness of the hydride complex and the ineffectiveness of the chloro, complex in the catalysis. It is learned that the presence of a Ru-(HH)-H-...-OH dihydrogen-bonding interaction in the transition state lowers the reaction barrier in the case of (eta(5)-C9H7)Ru(dppm)H, but in the chloro system, the corresponding transition state does not contain this type of interaction and the reaction barrier is much higher. A similar dihydrogen-bond-promoting effect is believed to be responsible for the catalytic activity of the hydrotris(pyrazolyl)borato (Tp) ruthenium complex TpRu(PPh3)(CH3CN)H in CH3CN hydration. The chloro analogue TpRu(PPh3)(CH3CN)Cl shows no catalytic activity.