Hydrogenolysis of [Cp(PMe(3))Rh(Me)(CH(2)Cl(2))](+)BAr'(4)(-) (4, Ar' = 3,5-C(6)H(3)(CF(3))(2)) in dichloromethane afforded the nonclassical polyhydride complex [Cp*PMe(3))Rh(H)(H(2))](+)BAr'(4)(-) (1), which exhibits a single hydride resonance at all accessible temperatures in the (1)H NMR spectrum. Exposure of solutions of 1 to D(2) or T(2) gas resulted in partial isotopic substitution in the hydride sites. Formulation of 1 as a hydride/dihydrogen complex was based upon T(1) (T(1)(min) = 23 ms at 150 K, 500 MHz), J(H-D) (ca. 10 Hz), and J(H-T) (ca. 70 Hz) measurements. The barrier (Delta G(++)) to exchange of hydride with dihydrogen sites was determined to be less than ca. 5 kcal/mol. Protonation of Cp(PMe(3))Rh(H)(2) (2) using H(OEt(2))(2)BAr'(4) resulted in binuclear species [(Cp(PMe(3))Rh(H))(2)(mu-H)](+)BAr'(4)(-) (3), which is formed in a reaction involving 1 as an intermediate. Complex 3 contains two terminal hydrides and one bridging hydride ligand which exchange with a barrier of 9.1 kcal/mol as observed by (1)H NMR spectroscopy. Additionally, the structures of 3 and 4, determined by X-ray diffraction, are reported.

Several dihydrogen complexes of ruthenium of the form [Cp/Cp*Ru(P-P)H(2)](+) (P-P = chelating diphosphine ligand) have been prepared by reaction of the corresponding neutral chloride complexes with H(2) in the presence of NaB(ArF)(4). Treatment with D(2) or T(2) 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.