1,3-Bisdiphenylphosphinoferrocenes: the unexpected 2,5,-dilithiation of dibromoferrocene towards a new area of ferrocene-ligand chemistry

1,1′-Dibromo-2,2′,5,5′-tetrakis(methylthio)ferrocene

The reaction of 1,1′-dibromoferrocene with three equivalents of LiTMP and Me2S2 produces a product mixture, from which 1,1′-dibromo-2,2′-bis(methylthio)ferrocene (4) can be isolated in moderate yield. Further treatment of the isolated compound 4 with two equivalents of LiTMP and Me2S2 also produced a mixture, from which the title compound 7 could be isolated. A crystal structure determination of 7 shows that the two cyclopentadienyl rings are oriented in such a way that a maximum number of S…Br contacts results. Intermolecular S…Br contacts, supported by S…S contacts, lead to a 1D-chain polymer in [1 0 0] direction.

Synthesis and Structures of 1,1′,2-Tribromoferrocene, 1,1′,2,2′-Tetrabromoferrocene, 1,1′,2,2′-Tetrabromoruthenocene: Expanding the Range of Precursors for the Metallocene Chemist’s Toolkit

The synthesis, characterisation, and isolation of 1,1′,2-tribromoferrocene and 1,1′,2,2′-tetrabromoferrocene, which are key synthons in ferrocene chemistry, are described. These compounds are prepared using α-halide assisted lithiation. The crystal structures of 1,1′,2-tribromoferrocene, 1,1′,2,2′-tetrabromoferrocene, 1,1′-dibromoruthenocene, and 1,1′,2,2′-tetrabromoruthenocene have been determined and are reported together with a brief discussion of the intramolecular forces involved in the crystal structures.

Halide-Mediated Ortho-Deprotonation Reactions Applied to the Synthesis of 1,2- and 1,3-Disubstituted Ferrocene Derivatives

The ortho-deprotonation of halide-substituted ferrocenes by treatment with lithium tetramethylpiperidide (LiTMP) has been investigated. Iodo-, bromo-, and chloro-substituted ferrocenes were easily deprotonated adjacent to the halide substituents. The synthetic applicability of this reaction was, however, limited by the fact that, depending on the temperature and the degree of halide substitution, scrambling of both iodo and bromo substituents at the ferrocene core took place. Iodoferrocenes could not be transformed selectively into ortho-substituted iodoferrocenes since, in the presence of LiTMP, the iodo substituents scrambled efficiently even at −78 °C, and this process had occurred before electrophiles had been added. Bromoferrocene and certain monobromo-substituted derivatives, however, could be efficiently ortho-deprotonated at low temperature and reacted with a number of electrophiles to afford 1,2- and 1,2,3-substituted ferrocene derivatives. For example, 2-bromo-1-iodoferrocene was synthesized by ortho-deprotonation of bromoferrocene and reaction with the electrophiles diiodoethane and diiodotetrafluoroethane, respectively. In this and related cases the iodide scrambling process and further product deprotonation due to the excess LiTMP could be suppressed efficiently by running the reaction at low temperature and in inverse mode. In contrast to the low-temperature process, at room temperature bromo substituents in bromoferrocenes scrambled in the presence of LiTMP. Chloro- and 1,2-dichloroferrocene could be ortho-deprotonated selectively, but in neither case was scrambling of a chloro substituent observed. As a further application of this ortho-deprotonation reaction, a route for the synthesis of 1,3-disubstituted ferrocenes was developed. 1,3-Diiodoferrocene was accessible from bromoferrocene in four steps. On a multigram scale an overall yield of 41% was achieved. 1,3-Diiodoferrocene was further transformed into symmetrically 1,3-disubstituted ferrocenes (1,3-R₂Fc; R = CHO, COOEt, CN, CH=CH₂).

Synthesis, transition metal chemistry and catalytic reactions of ferrocenylbis(phosphonite), [Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2]

The new metalloligand ferrocenylbis(phosphonite), [Fe(C5H4PR2)2 (R = OC6H3(OMe-o)(C3H5-p))], (2), is synthesized by the reaction of bis(dichlorophosphino)ferrocene Fe(C5H4PCl2)2 (1) with 4-allyl-2-methoxyphenol. The reactions of 2 with H2O2 and elemental sulfur or selenium afforded bischalcogenides, [Fe{C5H4P(E)(OC6H3(OMe-o)(C3H5-p))2}2] (3, E = O; 4, E = S; 5, E = Se), in good yield. The bis(phosphonite) reacts with group 6 metal carbonyls and group 10 metal dichloride precursors to produce the chelate complexes [{M(CO)4}Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2}] (6, M = Mo; 7, M = W) and [(MCl2)Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2] (8, M = Pd; 9, M = Pt). The palladium(ii) complex [(PdCl2)Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2] (8) is an efficient catalyst for the Suzuki-Miyaura cross-coupling reactions (TON up to 1.5 × 10(5)). The reaction of 2 with one equivalent of [RuCl2(η(6)-p-cymene)]2 yielded the binuclear complex [{Ru2Cl4(η(6)-p-cymene)2}Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2] (12) in good yield. Treatment of 2 with copper chloride in a 1 : 1 or 1 : 2 molar ratio resulted in the formation of a binuclear complex, [{(CuCl)Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2}2] (13), whereas a similar reaction of 2 with CuBr and CuI in a 1:2 or 1:2.5 molar ratio yielded the novel butterfly-like deca-nuclear complexes [Cu5(μ-X)5{Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2}2]2 (14, X = Br; 15, X = I). The reaction of 2 with two equivalents of [AuCl(SMe2)] afforded the digold complex [(AuCl)2Fe{C5H4P(OC6H3(OMe-o)(C3H5-p))2}2] (16), with the ligand exhibiting bridged-bidentate mode of coordination. Additionally, some complexes were studied by cyclic voltammetry. The crystal structures of complexes 8, 9, 12, 15 and 16 were determined using X-ray diffraction studies.

Stereoselective synthesis of chiral, non-racemic 1,2,3-tri- and 1,3-disubstituted ferrocene derivatives

Chiral, non-racemic 1,2,3-trisubstituted ferrocene derivatives are accessible from monosubstituted ferrocenes through two sequential ortho-deprotonation reactions; removal of the central substituent gives 1,3-disubstituted ferrocenes.