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

Abstract

Treatment of [Rh(β-diketonato)(cod)] with CO resulted in better yields of [Rh(FcCOCHCOR)(CO) 2] than by treating [Rh(Cl)(CO) 2] 2 with FcCOCH 2COR, R = CF 3 (Hfctfa), CH 3 (Hfca), Ph (Hbfcm, Ph = phenyl) and Fc (Hdfcm, Fc = ferrocenyl). The single crystal structure of the fctfa rhodium(I) complex [C 16H 10F 3FeO 4Rh], monoclinic, C 2/c(15), a = 13.266(3) Å, b = 19.553(3) Å, c = 13.278(3) Å, β = 100.92(2)°, Z = 8 showed both rotational and translational displacement disorders for the CF 3 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, χ R, of the R groups on the β-diketonato ligands, as well as to the p K a ′ values of the free β-diketones. Anodic peak potentials, E pa,Rh, for the dominant cyclic voltammetry peak associated with rhodium(I) 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.