The ferrocenylthiophenes 2,3-Fc 2 -c C 4 H 2 S (9), 2,4-Fc 2 -c C 4 H 2 S (10), and 2,3,4-Fc 3 -c C 4 HS (11) have been prepared by a 2-or 3-fold Negishi cross-coupling reaction of the appropriate bromo thiophenes 5−7 with FcZnCl (8; Fc = Fe(η 5 -C 5 H 4 )(η 5 -C 5 H 5 )) in the presence of either [Pd(PPh 3 ) 4 ] or [Pd(CH 2 CMe 2 P t Bu 2 )(μ-Cl)] 2 as catalyst. Concerning electron transfer studies on ferrocenyl-substituted aromatic heterocycles, the electrochemistry as well as in situ UV−vis−near-IR spectroelectrochemistry highlight the electrochemical properties of these compounds in a series of mono-, di-, tri-, and tetraferrocenylthiophenes, including 2-Fc- 12), and 2,3,4,5-Fc 4 -c C 4 S (13). These organometallic compounds display one (1, 2), two (3, 4, 9, 10), three (11, 12), or four (13) well-resolved electrochemically reversible one-electron-transfer processes using [N n Bu 4 ][B(C 6 F 5 ) 4 ] as the supporting electrolyte. The spectroelectrochemical studies reveal that ferrocenyl units placed in the α-position of the thiophene ring interact more strongly with the heterocycle than those in the β-position. Thus, the intensity of the ligand-to-metal charge transfer (LMCT) absorptions, caused by interactions between the thiophene core and the ferrocenyl moieties, decreases from 1 + to 2 + . Furthermore, in the series of diferrocenylthiophenes the interaction between the iron centers in the mono-oxidized compounds decreases in the series 3 + > 9 + > 10 + > 4 + . The structural properties of 10 were investigated by single-crystal X-ray diffraction studies, indicating that 10 possesses a syn conformation in the solid state with respect to the orientation of the two ferrocenyl units along the central thiophene core. Compound 10 is isomorphic with 3.

The electrochemical oxidation of ruthenocene, RuCp(2) (Cp = eta(5)-C(5)H(5)), 1, has been studied in dichloromethane using a supporting electrolyte containing either the [B(C(6)F(5))(4)](-) (TFAB) or the [B(C(6)H(3)(CF(3))(2))(4)](-) (BArF(24)) counteranion. A quasi-Nernstian process was observed in both cases, with E(1/2) values of 0.41 and 0.57 V vs FeCp(2) in the respective electrolyte media. The ruthenocenium ion 1(+) equilibrates with a metal-metal bonded dimer [Ru(2)Cp(4)](2+), 2(2+), that is increasingly preferred at low temperatures. Dimerization equilibrium constants determined by digital simulation of cyclic voltammetry (CV) curves were in the range of 10(2)-10(4) M(-1) at temperatures of 256 to 298 K. Near room temperature, and particularly when BArF(24) is the counteranion, the dinuclear species [Ru(2)Cp(2)(sigma:eta(5)-C(5)H(4))(2)] (2+), 3(2+), in which each metal is sigma-bonded to a cyclopentadienyl ring, was the preferred electrolytic oxidation product. Cathodic reduction of 3(2+) regenerated ruthenocene. The two dinuclear products, 2(2+) and 3(2+), were characterized by (1)H NMR spectroscopy on anodically electrolyzed solutions of 1 at low temperatures in CD(2)Cl(2)/[NBu(4)][BArF(24)]. The variable temperature NMR behavior of these solutions showed that 3(2+) and 2(2+) take part in a thermal equilibrium, the latter being dominant at the lowest temperatures. Ruthenocene hydride, [1-H](+), was also identified as being present in the electrolysis solutions. The oxidation of ruthenocene is shown to be an inherent one-electron process, giving a ruthenocenium ion which is highly susceptible to reactions that allow it to regain an 18-electron configuration. In a dry non-donor solvent, and in the absence of nucleophiles, this electronic configuration is attained by self-reactions involving formation of Ru-Ru or Ru-C bonds. The present data offer a mechanistic explanation for the previously described results on the chemical oxidation of osmocene (Droege, M.W.; Harman, W.D.; Taube, H. Inorg. Chem. 1987, 26, 1309) and are relevant to the manner in which sigma:eta(5)-C(5)H(4)-complexes of other second and third-row metals are formed.

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4,4-trifluorobutane-1,3-dione (ferrocenoyltrifluoroacetone, Hfctfa, pK a 1 = 6.53 ± 0.03), 4,4,4trichloro-1-ferrocenylbutane-1,3-dione (trichloroferrocenoylacetone, Hfctca, pK a 1 = 7.15 ± 0.02), 1-ferrocenylbutane-1,3-dione (ferrocenoylacetone, Hfca, pK a 1 = 10.01 ± 0.02), 1-ferrocenyl-3-phenylpropane-1,3-dione (benzoylferrocenoylmethane, Hbfcm, pK a 1 = 10.41 ± 0.02) and 1,3-diferrocenylpropane-1,3-dione (diferrocenoylmethane, Hdfcm, pK a 1 = 13.1 ± 0.1) were prepared by Claisen condensation of acetylferrocene with an appropriate ester under the influence of sodium amide, sodium ethoxide or lithium diisopropylamide. The group electronegativity of the ferrocenyl group is 1.87 (Gordy scale) as inferred from a linear β-diketone pK a 1 group electronegativity relationship as well as from a linear methyl ester IR carbonyl stretching frequency-group electronegativity relationship. Complexes [Rh(β-diketone)(cod)] were obtained in yields approaching 80% by treating the β-diketones with [Rh 2 Cl 2 (cod) 2 ], while the copper() chelates form just as readily. Treatment of all [Rh(β-diketone)(cod)] complexes with 1,10-phenanthroline (phen) and some of its derivatives resulted in substitution of the β-diketone ligand to form [Rh(cod)(phen)] ϩ . The uncomplexed β-diketones are increasingly stable towards the OH Ϫ nucleophile in the order Hdfcm (apparent most unstable) < Hfctfa < Hbfcm < Hfctca < Hfca (most stable). Asymmetric enolisation in the direction furthest from the ferrocenyl group was observed for all β-diketones. This finding is considered to be the result of resonance driving forces rather than inductive electronic effects of substituents on the pseudo-aromatic β-diketone core.