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.

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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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A series of poly(ferrocenylsilanes) with methylated cyclopentadienyl (Cp) rings [Fe(η-C5-MexH4-x)(η-C5MeyH4-y)SiMe2]n (2a-e) (a, x ) 0, y ) 0; b, x ) 1, y ) 1 (Cp-Me groups at random positions); c, x ) 1, y ) 1 (Cp-Me groups at 3,3′ positions); d, x ) 4, y ) 0; e, x ) 4, y ) 4) have been prepared by thermal ring-opening polymerization (TROP) of the corresponding silicon-bridged [1]ferrocenophanes Fe-(η-C5MexH4-x)(η-C5MeyH4-y)SiMe2 (1a-e). DSC analysis revealed that increasing methylation of the ferrocenophane Cp rings resulted in increasing onset temperatures for the TROP reaction but did not significantly affect the enthalpy of polymerization, ∆Hp. Poly(ferrocenylsilanes) 2b-d were soluble in common organic solvents and were characterized by IR, 1 H, 13 C, and 29 Si NMR spectroscopy, and elemental analysis. The molecular weights of these polymers were estimated to be in the range of Mw ) 1.8 × 10 5 to 4.1 × 10 5 and Mn ) 9.4 × 10 4 to 2.8 × 10 5 by GPC in THF versus polystyrene standards. The fully methylated poly(ferrocenylsilane) 2e was insoluble in common organic solvents and was characterized by IR, 13 C and 29 Si CP-MAS NMR, and elemental analysis. The electrochemical behavior of 2b-d in CH2Cl2 solution was investigated by cyclic voltammetry, and these polymers each exhibited two reversible oxidation waves, consistent with significant electronic interactions between the iron centers. Increasing Cp methylation led to the expected decrease in half-wave oxidation potentials, relative to nonmethylated 2a. DSC analysis showed that 2b-d exhibit weak glass transitions which shift to higher temperature with increasing methylation. No melting transitions were detected by DSC for these polymers, and WAXS analysis confirmed that the polymers were amorphous and indicated that the average interchain distance increases with increasing Cp methylation. TGA of 2a-d found decreasing thermal stability with regard to weight loss upon increasing methylation. The microstructure of polymer 2d provided insight into the polymerization mechanism and was consistent with polymerization via nonselective cleavage of Cp-Si (as opposed to Cp-Fe) bonds. The reactions of 2a, 2b, 2d, and 2e with tetracyanoethylene (TCNE) were investigated. Whereas 2a did not react, the Cp-methylated analogues 2b, 2d, and 2e yielded dark solids 3b, 3d, and 3e, which were soluble in polar organic solvents. IR and microanalytical data indicated that the products contain oxidized polymer and a mixture of polycyano counteranions. Bulk solid-state magnetic susceptibility data indicated that 3e obeys the Curie-Weiss law, with µeff ) 2.0 µB, and θ ) -1.1 K. In contrast to recent reports on TCNE-oxidized oligo(ferrocenylsilanes), no evidence was found for any long-range cooperative spin-spin interactions at low temperature.