Photochemistry of π-cyclopentadienylcarbonylmetal halides in dimethyl sulphoxide and related solvents

Abstract

The principal product when solutions in dimethyl sulphoxide or pyridine of π-cyclopentadienylcarbonylmetal halides of Fe, Mo, and W are irradiated at long wavelengths (λ > 400 nm) is a dimer: this is [(π-C₅H₅)Fe(CO)₂]₂ in the case of Fe (indicating loss of halogen) but appears to be [(π-C₅H₅)M(CO)₂Cl]₂ for Mo and W; free cyclo-pentadiene and chloride ion are also produced in the case of Fe. The reactions do not proceed in non-polar solvents. At shorter wavelengths (λ > 280 nm) the principal product in all cases is a dimeric species which could not be isolated, but which spectral data suggest to correspond to displacement of one CO molecule by solvent from the dimers obtained at longer wavelengths; moreover i.r. and n.m.r. spectral profiles of the λ > 280 nm reaction indicate that the latter are essential intermediates in all three cases.