Cyclic voltammetry of ferrocene-containing β-diketones as a tool to obtain group electronegativities.: The structure of 3-ferrocenoyl-1,1,1-trifluoro-2-hydroxyprop-2-ene

Formal reduction potentials (E degrees' values vs. Ag/Ag+ given in parentheses) in acetonitrile of 1-ferrocenyl-4,4,4-trifluorobutane-1,3-dione (ferrocenoyltrifluoroacetone, Hfctfa, 0.394 V), 1-ferrocenyl-4,4,3-trichlorobutane-1,3-dione (ferrocenoyltrichloroacetone, Hfctca, 0.370 V), 1-ferrocenylbutane-1,3-dione (ferrocenoylacetone, Hfca, 0.313 V), 1-ferrocenyl-3-phenylpropane-1,3-dione (benzoylferrocenoylmethane, Hbfcm, 0.306 V), and 1,3-diferrocenylpropane-1,3-dione (diferrocenoylmethane, Hdfcm, 0.265 and 0.374 V for the two electrochemically nonequivalent ferrocenyl groups) were determined. A linear relationship between observed group electronegativity, chi, and E degrees' as well as observed infrared carbonyl stretching frequencies of methyl eaters of the type RCOOMe resulted in average chi-values, on the Gordy scale, of 1.87 for the ferrocenyl group and 2.82 for the ferrocenium group. A single crystal X-ray structure determination of Hfctfa (monoclinic, P2(1)/n, Z = 4, R = 0.029) showed that this beta-diketone crystallizes in the enol form. Asymmetric enolization in a direction furthest from the aromatic ferrocenyl group was observed.