Electrochemical Illumination of Intramolecular Communication in Ferrocene-Containing tris-β-Diketonato Aluminum(III) Complexes; Cytotoxicity of Al(FcCOCHCOCF3)3

The series of ferrocene-containing tris-β-diketonato aluminum­(III) complexes [Al­(FcCOCHCOR)3] (R = CF3, 1; CH3, 2; C6H5, 3; and Fc = ferrocenyl = Fe­(η5-C5H5)­(η5-C5H4), 4) were synthesized and investigated structurally and electrochemically; complex 1 was subjected to cytotoxicity tests. 1H NMR-spectroscopy distinguished between the mer and fac isomers of 2 and 3. Complex 1 existed only as the mer isomer. A single crystal X-ray crystallographic determination of the structure of a mer-isomer of Al­(FcCOCHCOCF3)3, 1, (Z = 4, space group P212121) demonstrated extensive delocalization of all bonds which explained the pronounced electrochemically observed intramolecular communication between molecular fragments. In contrast to electrochemical studies in CH2Cl2/[N­(nBu)4]­[PF6], the use of the supporting electrolyte [N­(nBu)4]­[B­(C6F5)4] allowed identification of all Fc/Fc+ electrochemical couples by cyclic and square wave voltammetry for 1–4. For R = Fc, formal reduction potentials of the six ferrocenyl groups were found to be E°′ = 33, 123, 304, 432, 583, and 741 mV versus free ferrocene respectively. Complex 1 (IC50 = 10.6 μmol dm–3) was less cytotoxic than the free FcCOCH2COCF3 ligand having IC50 = 6.8 μmol dm–3 and approximately 2 orders of magnitude less toxic to human HeLa neoplastic cells than cisplatin (IC50 = 0.19 μmol dm–3).