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 = CF(3), 1; CH(3), 2; C(6)H(5), 3; and Fc = ferrocenyl = Fe(η(5)-C(5)H(5))(η(5)-C(5)H(4)), 4) were synthesized and investigated structurally and electrochemically; complex 1 was subjected to cytotoxicity tests. (1)H 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(FcCOCHCOCF(3))(3), 1, (Z = 4, space group P2(1)2(1)2(1)) demonstrated extensive delocalization of all bonds which explained the pronounced electrochemically observed intramolecular communication between molecular fragments. In contrast to electrochemical studies in CH(2)Cl(2)/[N((n)Bu)(4)][PF(6)], the use of the supporting electrolyte [N((n)Bu)(4)][B(C(6)F(5))(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 (IC(50) = 10.6 μmol dm(-3)) was less cytotoxic than the free FcCOCH(2)COCF(3) ligand having IC(50) = 6.8 μmol dm(-3) and approximately 2 orders of magnitude less toxic to human HeLa neoplastic cells than cisplatin (IC(50) = 0.19 μmol dm(-3)).