The silicon-bridged [1]ferrocenophanes Fe(η-C5H4)2SiRR‘ [3 (R = Me, R‘ = Cl), 4 (R = R‘ = Cl)] with chlorine substituent(s) at silicon were prepared via the reaction of Fe(η-C5H4Li)2·TMEDA (TMEDA = tetramethylethylenediamine) with the chlorinated silanes MeSiCl3 and SiCl4, respectively. An X-ray diffraction study of 4 indicated that the cyclopentadienyl rings in this species are tilted by an angle of 19.2(4)°, typical of other structurally characterized silicon-bridged [1]ferrocenophanes. Thermal ring-opening polymerization (ROP) of 3 and 4 at 250 °C yielded the first high molecular weight poly(ferrocenylsilanes) with halogen substituents at silicon, [Fe(η-C5H4)2SiRR‘] n [7 (R = Me, R‘ = Cl), 8 (R = R‘ = Cl)]. Transition-metal-catalyzed polymerization of 3 and 4 with Pd and Pt catalysts also yielded polymers 7 and 8 in solution at room temperature. Polymer 7 was soluble in polar organic solvents and was characterized by 1H, 29Si, and 13C NMR and elemental analysis. In contrast, poly(ferrocenylsilane) 8 was found to be insoluble in organic solvents and this material was characterized by elemental analysis and derivatization. Substitution of the chlorine side groups in polymer 7 was achieved under mild conditions via reaction with the organolithium reagents MeLi, PhLi, and LiC⋮C(CH2)4H to afford the known polymers [Fe(η-C5H4)2SiMe2] n (2a) and [Fe(η-C5H4)2SiMePh] n (2d) and the new polymer [Fe(η-C5H4)2SiMeC⋮C(CH2)4H] n (9), respectively. The molecular weights for the completely halogen-substituted poly(ferrocenylsilanes) 2a, 2d, and 9 were estimated by gel permeation chromatography in THF to be in the range of M w = 7.4 × 104 to 1.7 × 105 and M n = 3.6 × 104 to 1.1 × 105 versus polystyrene standards. Substitution of the chlorine atoms in 8 was also demonstrated by reaction of the polymer with MeLi to give 2a.

The first chalcogen-bridged [1]ferrocenophanes Fe(η-C5H3R)2E (6, E = S, R = H; 7, E = Se, R = H; 12, E = S, R = Me) have been synthesized and characterized both structurally and spectroscopically. Synthesis of sulfur- and selenium-bridged species 6 and 7 was achieved by the reaction of dilithioferrocene·TMEDA (TMEDA = tetramethylethylenediamine) with bis(phenylsulfonyl) sulfide S(O2SPh)2 and selenium diethyldithiocarbamate Se(S2CNEt2)2, respectively, in 20−30% yields. Structural characterization of both 6 and 7 revealed highly strained structures with tilt-angles between the cyclopentadienyl ligands of 31.05(10)° and 26.4(2)°, respectively. Compounds 6 and 7 are purple and red-purple, respectively; comparison of the structures of known [1]ferrocenophanes 1 showed that when the second period (from group 14−16) is traversed, there is a substantial increase in cyclopentadienyl ring-tilting in main group element bridged [1]ferrocenophanes, and the lowest energy UV/vis absorption peaks become increasingly red-shifted. Extended Hückel MO calculations were performed and, consistent with this observation, predicted a decrease in the HOMO−LUMO gap as the ring-tilt increases. Thermal ring-opening polymerization (ROP) of both 6 and 7 afforded the insoluble poly(ferrocenyl sulfide) [Fe(η-C5H4)2S] n 8 and poly(ferrocenyl selenide) [Fe(η-C5H4)2Se] n 9, respectively. Differential scanning calorimetry studies of the ROP process provided estimates of the strain energies of 6 and 7 which were ca. 130(±20) and 110(±20) kJ mol-1, respectively. Anionic ROP of 6 also yielded the insoluble poly(ferrocenyl sulfide) 8. However, linear soluble dimeric and trimeric trimethylsilyl-capped oligo(ferrocenyl sulfides) 10b and 11b were synthesized by the reaction of 6 with dilithioferrocene·TMEDA followed by the addition of Me3SiCl and were characterized spectroscopically, electrochemically, and, for 11b, by X-ray diffraction, and provide useful models for the analogous high polymer. The dimethylated sulfur-bridged species 12 was prepared as a mixture of isomers from the reaction between dilithiodimethylferrocene·TMEDA and S(O2SPh)2, and X-ray structural characterization of a single isomer 12a showed the presence of a large tilt-angle of 31.46(8)°. Thermal and anionic ROP of the isomer mixture 12 afforded the first soluble poly(ferrocenyl sulfide) [Fe(η-C5H3Me)2S] n 13 which was characterized by 1H and 13C NMR, elemental analysis, thermogravimetric analysis, and gel permeation chromatography. Cyclic voltammetric studies of 13 showed the presence of two reversible oxidation waves with a redox coupling ΔE = ca. 0.32 V, which is consistent with the presence of significantly stronger M···M interactions compared to those present in other ring-opened poly(ferrocenes) derived from [1]ferrocenophanes.

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