PHOTOSUBSTITUTION REACTIONS OF M(CO)(4)(1,10-PHENANTHROLINE) (M=MO,W)- INFLUENCE OF ENTERING LIGAND, IRRADIATION WAVELENGTH, AND PRESSURE

The influence of the entering nucleophile, irradiation wavelength, and pressure on the quantum yield for the photosubstitution of M(CO)(4)ph en (M = Mo, W) to produce M(CO)(3)(L)phen (L = PMe(3), PPh(3)) was inv estigated in toluene at 298 K. From the pressure dependence of the qua ntum yield apparent volumes of activation could be determined as a fun ction of irradiation wavelength. These could be analyzed in terms of c ontributions arising from dissociative ligand field excitation and ass ociative metal-to-ligand charge transfer excitation. The influence of steric hindrance on the entering ligand (PPh(3) > PEt(3) > PMe(3)) con trols the contribution of the associative charge-transfer photosubstit ution reaction. An overall mechanistic picture is presented and discus sed in reference to available literature data.