Photochemistry of ferrocenyl ketones and acids in dimethyl sulphoxide and related solvents

Compounds of the type FcCOAr, FcCOR (R = Alkyl), and FcCHO undergo photoaquation (λ > 280 nm) in wet dimethyl sulphoxide, pyridine, dimethylformamide, and related solvents to give a cyclopentadienyliron salt of the acid ArCO2H or RCO2H together with a molecule of free cyclopentadiene derived from the originally substituted ring. At shorter wavelengths in DMSO a secondary reaction gives rise to the intense purple colouration described previously. Ferrocenecarboxylic acid undergoes similar consecutive changes in these solvents yielding initially a carboxylate and free cyclopentadiene, but then CO2 and a new carboxylate from which starting material could be recovered in 48% yield. With shorter wavelength light a purple colouration developed. The esters of this acid were also found to be photosensitive but subject to strong autoretardation.