Synthesis and characterization of ReCl(H2)(AsMePh2)4, a classical hydride complex;: reexamination of ReCl(H2)(PMePh2)4 and theoretical calculations on model compounds

The synthesis of ReCl(H-2)(AsMePh2)(4) is reported and verified on the basis of H-1 NMR and FAB-MS. The minimum T-1 time for the metal-bonded hydrogen atoms was determined to be 44 ms (-78 degreesC) and 89 (-48 degreesC) ms at 200 and 400 MHz, respectively. From this minimum T-1 time, and, allowing for contributions from other nuclei to the relaxation, a metal-bonded H to H atom distance of 1.57 Angstrom can be assessed. The complex is reversibly oxidized at a potential E-1/2(ox) = +0.07 V. The J(HD) coupling in the related ReCl(HD)(AsMePh2)(4) compound was at 3.3 Hz. These data for ReCl(H-2)(AsMePh2)(4) suggest that this molecule contains classical hydrides, and interpretations on T-1 and X-ray data published previously for ReCl(H-2)(PMePh2)(4) suggest that this molecule contains a very long metal-bonded H-H interaction of 1.39 Angstrom. Theoretical calculations on model compounds ReCl(H-2)(XR3)(4) (X = P, As; R = H, Me) give virtually identical average d(H-H) values of 1.5 (XH3) and 1.63 (XMe3) Angstrom.