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Compounds of the type FcCOAr, FcCOR (R = Alkyl), and FcCHO undergo photoaquation (A > 280 nm) in wet dimethyl sulphoxide, pyridine, dimethylformamide, and related solvents to give a cyclopentadienyliron salt of the acid ArC0,H or RC0,H 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 CO, 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. Warwick, Coventry CV4 7ALNOT only is ferrocene itself apparently remarkably inert to photo-irradiation except in chlorocarbon solvents: but the presence of a ferrocenyl group (Fc) in a molecule containing a photoactive functional group, such as that of an aromatic carbonyl compound, can impart a remarkable change in the level and direction of photoreactivity.2 Bozak has summarised the several attempts to photoreduce benzoylferrocene using such solvents as propan-2-01 which are well known to reduce benzophenone to benzpinacol via the triplet state of the solute in a quantum yield of almost one. Nesmeyanov has found ferrocene-1 ,l'-dicarboxylic 3 and -disulphonic acids to undergo metal-ring cleavage on prolonged photolysis in aqueous or aqueous-alkaline solution to give derivatives of cyclopentadiene or its dimer. An interesting report of Tarr and Wiles refers to a somewhat greater photoreactivity of 1 ,l'-dibenzoylferrocene towards propan-1-01 and methanol and brief reference is given to a relatively rapid colour change to deep purple in the solvents, pyridine, dimethyl sulphoxide (DMSO), and dimethylformamide (DMF) (but not acetonitrile), but no attempt was made to characterise these reactions further. One possible explanation for the colour change lies in the formation of a ferrocene ketyl radical-anion FcCOPh-which has been characterised by e.s.r. spectroscopy,697 and we report here a detailed account of the relatively rapid photoreaction of benzoylferrocene in these particular solvents and observations on a number of related compounds of the general formula FcCOX where X = Ph, Ar, Me, H, OH, OR, and NH,: our results indicate that the photoreaction does not involve radicals derived from ferrocene but is rather a photoaquation involving solvent impurity followed by E. Koerner von Gustorf and F. W. Grevels, Fortsclzr. Chem.

Benzoylferrocene photoreacts with water in scopy ; a variety of other or-carbonylferrocenes are photoreactive in these solvent systems to give products which solvents such as dimethyl sulphoxide and pyridine to yield cyclopentadienyliron benzoate and free cyclo-may also contain carboxylate groups. pentadiene identified by Lr., u.v., and n.m.r. spectro-

The principal product when solutions in dimethyl sulphoxide or pyridine of x-cyclopentadienylcarbonyimetal halides of Fe, Mo, and W are irradiated at long wavelengthsin the case of Fe (indicating loss of halogen) but appears to be [(X-C~H~)M(CO),CJ], for Mo and W; free cyclopentadiene and chloride ion are also produced in the case of Fe. The reactions do not proceed in non-polar solvents. At shorter wavelengths (A > 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 h > 280 nm reaction indicate that the latter are essential intermediates in all three cases. Coventry CV4 7ALTHE primary process dominating the photochemistry of many metal and arenemetal carbonyls is that of elimination of one molecule of CO to leave an unsaturated intermediate, which rapidly co-ordinates with a solvent molecule S,1~2 vix.unless it is prepared either in an inert in which case it can be rendered sufficiently stable for i.r. and U.V. examination, or in a non-co-ordinating solvent, in which case the end-product corresponds to a disproportiona-tionJ6 e.g. GCr(CO), + 5Cr(CO), + Cr which clearly involves a sequence of several steps. Evidence for the unsaturated intermediates has also been obtained from room-temperature flash photolysis