Intermolecular H...H Bonding and Proton Transfer in Semisandwich Re and Ru Complexes

The reactions of transition metal (TM) hydrides (Cp)Re(H)(NO)(CO), (Cp)Ru(H)(CO)(PH3), and (Cp)Re(H)(NO)(PH3) with poor, moderate, and strong proton donors HR (H2O, HOCF3, and H3O+) are studied using DFT B3PW91. The reaction pathway depends on the relative proton-attracting powers of the TM and hydride H atoms, as well as on the proton donor ability of HR. In the case where these two atoms have comparable basicity, (Cp)Re(H)(NO)(CO) forms an intermolecular H···H bonding intermediate upon reaction with both poor and strong proton donors H2O and H3O+. This is followed by rearrangement to η2-H2 by proton transfer over a very small barrier. The reaction of (Cp)Ru(H)(CO)(PH3) with its highly nucleophilic hydride yields H···H bonding complexes with moderate proton donor HOCF3, whereas the strong donor H3O+ produces only the η2-H2 structure. Rapid rearrangement of η2-H2 to cis-dihydride is possible although the trans-dihydride is more stable. For both types of hydride, a reaction pathway through a H···H bonding ...