PHOTOCHEMICAL HETEROLYSIS OF THE METAL-METAL BOND IN (ME3P)(OC)4OSW(CO)5

The photochemistry of (Me3P)(OC)4OsW(CO)5 (1), a molecule with a dative covalent metal−metal bond, was investigated. The results indicate that the photoprocess is heterolytic cleavage of the metal−metal bond, rather than homolytic cleavage as is found in compounds with nondative covalent metal−metal bonds. The principal evidence for heterolysis comes from the irradiation (λ > 400 nm) of 1 in benzene in the presence of PPh3. The major products were Os(CO)4(PMe3), Os(CO)3(PMe3)(PPh3), and W(CO)5(PPh3). These products are consistent with a pathway that involves initial heterolysis to form Os(CO)4(PMe3) and W(CO)5 followed by trapping of the coordinatively unsaturated W(CO)5 species with PPh3. (Control experiments showed that Os(CO)3(PMe3)(PPh3) forms from Os(CO)4(PMe3) and PPh3 under the reaction conditions.) Primary photoprocesses involving either M−CO bond dissociation or Os−W bond homolysis are incompatible with the results of other experiments. For example, when the irradiation of 1 was carried out under...