Electrochemical illumination of intramolecular communication in ferrocene-containing tris -β-diketonato aluminum(III) complexes; Cytotoxicity of Al(FcCOCHCOCF _3) _3

摘要

The series of ferrocene-containing tris-β-diketonato aluminum(III) complexes [Al(FcCOCHCOR) _3] (R = CF _3, 1; CH _3, 2; C _6H _5, 3; and Fc = ferrocenyl = Fe(η ~5- C _5H _5)(η ~5-C _5H _4), 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(FcCOCHCOCF _3) _3, 1, (Z = 4, space group P2 _12 _12 _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 _2Cl _2/[N(~nBu) _4][PF _6], the use of the supporting electrolyte [N(~nBu) _4][B(C _6F _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 _2COCF _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)).