Synthetic, electrochemical and structural aspects of a series of ferrocene-containing dicarbonyl β-diketonato rhodium(I) complexes

Treatment of [Rh(beta-diketonato)(cod)] with CO resulted in better yields of [Rh(FcCOCHCOR)(CO)(2)] than by treating [Rh(Cl)(CO)(2)](2) with FcCOCH(2)COR, R = CF3 (Hfctfa), CH3 (Hfca), Ph (Hbfcm, Ph = phenyl) and Fc (Hdfcm, Fc ferrocenyl). The single crystal structure of the fctfa rhodium(I) complex [C16H10F3FeO4Rh], monoclinic, C 2/c(15), a 13.266(3) angstrom, b = 19.553(3) angstrom, c = 13.278(3) angstrom, beta = 100.92(2)degrees, Z = 8 showed both rotational and translational displacement disorders for the CF3 group. An electrochemical study revealed that the formal reduction potential, E-0 ', for the electrochemically reversible one electron oxidation of the ferrocenyl group varied between 0.304 (for the fctfa complex) and 0.172 V (for the dfcm complex) versus Fc/ Fc(+) in a manner that could be directly traced to the group electronegativities, chi(R), of the R groups on the beta-diketonato ligands, as well as to the pK '(a) values of the free beta-diketones. Anodic peak potentials, E-pa.Rh,E- for the dominant cyclic voltammetry peak asso- ciated with rhodium(l) oxidation were between 0.718 (bfcm complex) and 1.022 V (dfcm complex) versus Fc/Fc '. Coulometric experiments implicated a second, much less pronounced anodic wave for the apparent two-electron Rh-I oxidation that overlaps with the ferrocenyl anodic wave and that the redox processes associated with these two Rh-I oxidation waves are in slow equilibrium with each other. (c) 2005 Elsevier B.V. All rights reserved.