Photochemical reduction of CpW(CO)3CH3 (Cp = η5-C5H5) to CpW(CO)3 -; An isolobal analogy to the disproportionation of Cp2Mo2(CO)6

Irradiation (λ > 380 nm) of CpW(CO)₃Me in inert solvents in the presence of PPh₃ gives [PPh₃CH₃ ⁺][CpW(CO)₃ ^-] as well as the substitution product CpW(CO)₂(PPh₃)Me (φ_{disappearance CpW(CO)3Me} = 0-45 ± 0.005, φ_{appearance CpW(CO)3-} = 0.04 ± 0.01). The mechanism of CpW(CO)₃ ^- formation was studied. Experiments suggest that CpW(CO)₂(PPh₃)Me may be an intermediate in the reaction but direct reductive elimination of PPh₃Me⁺ from this species or from CpW(CO)(PPh3)2Me was ruled out. Experiments using PTol₃ demonstrated that PAr₃Me⁺ (Ar = aryl) is formed from exogenous, not coordinated, phosphine. The mechanism proposed for the reduction of CpW(CO)₃Me involves the intermediate formation of phosphoranyl radicals, -PPh₃Me, formed by addition of Me radicals (from W-CH₃ homolysis) to PPh₃. Phosphoranyl reduction of a variety of metal species which are present in solution is shown to lead to CpW(CO)₃ ^-. The proposed mechanism is isolobal with a mechanism we proposed for the photochemical disproportionation of metal-metal bonded dimers (e.g., Cp₂Mo₂(CO)₆) involving 19-valence-electron intermediates.