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

Abstract

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.

Studies on Cage‐Type Tetranuclear Metal Clusters with Ferrocenylphosphonate Ligands

“…[38,39] This is because metal phosphonates normally form poorly crystalline compounds and the ferrocene moiety is sensitive to oxygen, water, heat, and light when it is attached with electron-withdrawing substituents on the cyclopentadienyl (Cp) rings. [40][41][42] Until now, only Henderson et al have reported platinum-ferrocenylphosphonate complexes and studied their antitumor activity [39] and Bideau et al have reported a zinc(ii)-ferrocenylphosphonate polymer with a unique 2D ferrocene arrangement anchored on a 1D Zn-O-P-O-Zn backbone. [38] To the best of our knowledge, metalferrocenylphosphonate cage complexes have not been reported.…”

Tetrametallic macrocyclic frameworks constructed from ferrocenedicarboxylato and 2,2′-bipyridine: synthesis, molecular structures and characteristics

“…It has been reported that electron-withdrawing substituent on the cyclopentadienyl ring for ferrocene derivatives may provide a greater photolability, and can undergo photolysis in some solvents to cause both ringmetal and ring-carbonyl cleavages, giving Fe 2þ cation and some free radicals [34][35][36][37][38]. If the mixture of metal ions, 2,2 0 -bpy, 1,1 0 -ferrocenedicarboxylic acid and NaOH in methanol-water solution are under light, it could turn from orange to dark-brown solution and then produce brown precipitate, whose composition cannot be identified, compounds (1)-(4) could not be obtained.…”

Synthesis and structures of three heterobimetallic compounds based on a new ferrocenyl pyridine ligand

“…All calculations were done with SHELX-97 [19]. Further details are given in Ferrocene derivatives bearing electron-withdrawing groups undergo photolysis in some solvents to cause cleavage of both ring-metal and ring-carbonyl, giving free Fe 2þ cation and free radicals [20][21][22][23]. Thus, all procedures should be performed in the dark.…”