89579-59-9Relevant articles and documents
Photochemical heterolysis of the metal-metal bond in (Me3P)(OC)4OsW(CO)5
Male, Jonathan L.,Pomeroy, Roland K.,Tyler, David R.
, p. 3431 - 3438 (2008/10/08)
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 CO, the quantum yield for disappearance of 1 increased to 0.28 ± 0.05 from its value of 0.13 ± 0.01 under N2, a result inconsistent with M-CO dissociation as the primary photoprocess. Likewise, control experiments showed that [W(CO)5.1] was readily trapped under the reaction conditions, but all attempts to trap [W(CO)5.1] (one of the expected homolytic primary photoproducts) with the metal-radical traps benzyl chloride, CCl4, or TMIO (1,1,3,3-tetramethylisoindoline-2-oxyl) during the photolysis of 1 were fruitless. Compound 1 reacted photochemically with CCl4 to form fac-Os(CO)3(PMe3)Cl2 (fac-2) and W(CO)6. The fac-Os(CO)3(PMe3)Cl2 product is likely formed by a secondary photolysis of Os(CO)4(PMe3). Control experiments showed that irradiation of Os(CO)4(PMe3) in CCl4 initially formed a compound believed to be Os(CO)3(PMe3)(CCl3)-Cl, which in the presence of W(CO)5 then reacted to form fac-Os(CO)3(PMe3)Cl2. Small amounts of W(CO)6 (8percent) were also produced in the photochemical reaction of 1 with PPh3. An experiment in a more viscous solvent system indicated that W(CO)6 is not formed in a CO abstraction reaction involving the [(Me3P)(OC)4Os, W(CO)5] solvent cage pair. The formation of W(CO)6 is attributed to a second (minor) heterolytic pathway involving an intermediate with a bridging CO that directly yields W(CO)6 and Os(CO)3(PMe3).
