title: Relationship between electrochemical potentials and substitution reaction rates of ferrocene-containing β-diketonato rhodium(I) complexes; cytotoxicity of [Rh(FcCOCHCOPh)(cod)].
abstract: A series of ferrocene-containing rhodium complexes of the type [Rh(FcCOCHCOR)(cod)] (cod = 1,5-cyclooctadiene) with R = CF(3), 1, (E(pa)(Rh) = 269; E(o)'(Fc) = 329 mV vs. Fc/Fc(+)), CCl(3), 2, (E(pa) = 256; E(o)' = 312 mV), CH(3), 3, (E(pa) = 177; E(o)' = 232 mV), Ph = C(6)H(5), 4, (E(pa) = 184; E(o)' = 237 mV), and Fc = ferrocenyl = (C(5)H(5))Fe(C(5)H(4)), 5, (E(pa) = 135; E(o)'(Fc1) = 203; E(o)'(Fc2) = 312 mV), have been studied electrochemically in CH(3)CN. Results indicated that the rhodium(I) centre is irreversibly oxidised to Rh(III) in a two-electron transfer process before the ferrocenyl fragment is reversibly oxidized in a one-electron transfer process. The peak anodic (oxidation) potential, E(pa), (in V vs. Fc/Fc(+)) of the rhodium core in 1-5 relates to k(2), the second-order rate constant for the substitution of (FcCOCHCOR)(-) with 1,10-phenanthroline in [Rh(FcCOCHCOR)(cod)] to form [Rh(phen)(cod)](+) in methanol at 25 °C with the equation lnk(2) = 39.5 E(pa)(Rh) - 3.69, while the formal oxidation potential of the ferrocenyl groups in 1-5 relates to k(2) by lnk(2) = 40.8 E(o)'(Fc)-6.34. Complex 4 (IC(50) = 28.2 μmol dm(-3)) was twice as cytotoxic as the free FcCOCH(2)COPh ligand having IC(50) = 54.2 μmol dm(-3), but approximately one order of magnitude less toxic to human HeLa neoplastic cells than cisplatin (IC(50) = 2.3 μmol dm(-3)).
authors.affiliation: Department of Chemistry, University of the Free State, P.O. Box 339, Bloemfontein, 9300, Republic of South Africa.
authors.forename: Jeanet
authors.initials: J
authors.lastname: Conradie
authors.forename: Jannie C
authors.initials: JC
authors.lastname: Swarts
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry* / Q000494:pharmacology*; D004563:Electrochemistry; D005296:Ferrous Compounds / Q000737:chemistry*; D006367:HeLa Cells; D006801:Humans; D020128:Inhibitory Concentration 50; D007700:Kinetics; D000075163:Metallocenes; D009942:Organometallic Compounds / Q000737:chemistry* / Q000494:pharmacology*; D012238:Rhodium / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D000970:Antineoplastic Agents; D005296:Ferrous Compounds; D000075163:Metallocenes; D009942:Organometallic Compounds; D012238:Rhodium; C004998:ferrocene