Synthesis and investigation of [Cp*(PMe3)Rh(H)(H2)]+ and its partially deuterated and tritiated isotopomers:: Evidence for a hydride/dihydrogen structure

Hydrogenolysis of [Cp*(PMe3)Rh(Me)(CH2Cl2)]+BAr'(-)(4) (4, Ar' = 3,5-C6H3(CF3)(2)) in dichloromethane afforded the nonclassical polyhydricle complex [Cp*(PMe3)Rh(H)(H-2)]+BAr'(-)(4) (1), which exhibits a single hydride resonance at all accessible temperatures in the H-1 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 (DeltaG(double dagger)) to exchange of hydride with dihydrogen sites was determined to be less than ca. 5 kcal/mol. Protonation of Cp*(PMe3)Rh(H)(2) (2) using H(OEt2)(2)BAr'(4) resulted in binuclear species [(Cp*(PMe3)Rh(H))(2)(mu-H)](4) 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 H-1 NMR spectroscopy. Additionally, the structures of 3 and 4, determined by X-ray diffraction, are reported.