Synthesis and Spectroscopic Properties of Elongated Ruthenium Dihydrogen Complexes:  Temperature and Isotope Dependence of H−H Distances

Several dihydrogen complexes of ruthenium of the form [Cp/Cp*Ru(P−P)H2]+ (P−P = chelating diphosphine ligand) have been prepared by reaction of the corresponding neutral chloride complexes with H2 in the presence of NaB(ArF)4. Treatment with D2 or T2 gas leads to incorporation of deuterium or tritium in the dihydrogen ligand. Measurement of the resulting H−D and H−T couplings as a function of the temperature and magnetic field gives results consistent with computational studies which predict that the H−H bond distance will increase with temperature and will be significantly shortened by isotopic substitution. The degree of the observed temperature dependence is found to be a critical function of the ancillary ligand set.