SOLUTION PHOTOCHEMISTRY OF ANIONIC METAL-CARBONYL HYDRIDE DERIVATIVES - SUBSTITUTION AND DIMER DISRUPTION PROCESSES IN MU-H[M(CO)5]2-(M=CR AND W)

Dimer disruption and photosubstitution of a carbon monoxide ligand has been observed in µ-H[M2(CO)10]- derivatives (M = Cr and W) upon irradiation into the lowest energy electronic transition bands. The photosubstitution chemistry of these derivatives has been demonstrated to proceed with a high quantum efficiency for CO loss, φ410 = 0.20 for M = Cr and φ366 = 0.45 for M = W. On the other hand, the quantum efficiency for dimer disruption in the presence of CO to afford M(CO)6 was considerably less, being 0.046 and 0.017 for the chromium and tungsten derivatives, respectively. When the incoming ligand was 13CO, the principal species formed was µ-H[M2(CO)9(13CO)]-, where the 13CO ligand is in an equatorial site. Both photoprocesses, dimer disruption and photosubstitution, were interpreted in terms of the net bonding changes arising from depopulation of the dπ orbitals on the metals and the coincident population of the metal-metal antibonding component of the ̜closed̝ three-center bond of the M-H-M moieties. © 1979, American Chemical Society. All rights reserved.