Synthesis by ligand exchange and electrochemistry of ruthenocenyl-containing β-diketonato complexes of titanocene. Structure of [TiCp2(RcCOCHCOCH3)][ClO4

Abstract

A new synthetic route involving ligand exchange towards a series of ruthenocenyl-containing β-diketonato titanocene complexes of the type [TiIV(C5H5)2(RcCOCHCOR)][ClO4] with Rc = RuII(C5H5)(C5H4) and R = C10F21 (1), CF3 (2), C6F5 (3), C10H21 (4), CH3 (5), Rc (6) and Fc = FeII(C5H5)(C5H4) (7) are described. The complex [TiIV(C5H5)2(RcCOCHCOCH3)][ClO4], 5, (Z = 4) crystallised in the monoclinic space group P21/n. A cyclic voltammetric electrochemical study in CH2Cl2/0.1 M [NBu4][B(C6F5)4] showed the one-electron transfer redox processes of the TiIII/TiIV and Rc/Rc+ couples exhibited irreversible electrochemical behaviour. In CH3CN/0.1 M [N(nBu)4][PF6], the ruthenocenyl couple switched to an electrochemically and chemically irreversible two-electron transfer redox couple, Rc/Rc2+, involving the RuIV redox centre. The redox potentials of the TiIII/TiIV, Rc/Rc+ and Rc/Rc2+ couples were in the range −642 < Eo′ < −1479 mV (both solvents), 1016 mV < Eo′ < 1034 mV (CH2Cl2) and 609 mV < Eo′ < 832 mV (CH3CN) vs. the free ferrocene couple, FcH/FcH+, respectively. The Fc/Fc+ redox process associated with 7 was observed at Eo′ = 0.259 (CH3CN) and 0.235 V (CH2Cl2). The cytotoxicity of [TiIV(C5H5)2(RcCOCHCOCF3)][ClO4], 2, against CoLo DM320 and HeLa cells, IC50 = 10.2 and 9.7 μmol dm−3 respectively, was found to be in the same order of magnitude as those of the free ligand, RcCOCH2COCF3.