Synthesis, Characterization, and Properties of Symmetrically Substituted, Ring-Opened Poly(ferrocenylalkoxy/aryloxysilanes)

Abstract

A novel and convenient route to the first poly(ferrocenylsilanes) with alkoxy and aryloxy substituents at silicon is reported. The reaction sequence involves (i) unexpectedly facile and clean halogen replacement at the bridging atom of a readily accessible dichlorosilyl-bridged [1]ferrocenophane Fe(η-C5H4)2SiCl2 (3) by OR groups via reactions with aliphatic alcohols and phenols in the presence of an HCl acceptor and (ii) thermal or transition metal-catalyzed ring-opening polymerization of the new [1]ferrocenophanes of structure Fe(η-C5H4)2Si(OR)2 (4). This allows the preparation of high molecular weight poly(ferrocenylsilanes) [Fe(η-C5H4)2Si(OR)2]n with side group substituents such as short chain alkoxy groups (5a−5b, R = OMe, OEt), fluorinated ethoxy groups (5c, R = OCH2CF3), long chain alkoxy groups (5d−5g, R = OBu, OHex, OC12H25, OC18H37), and aryloxy substituents (5h, 5i, and 5k, R = OPh, OPh-p-tBu, OPh-p-tBu, OPh-p-Ph) at silicon. The molecular structures of the [1]ferrocenophane monomers 4a and 4j have been studied by single-crystal X-ray diffraction, and these species possess strained structures with tilt angles between the planes of the cyclopentadienyl ligands of 18−19°. The new poly(ferrocenylsilanes) possess a wide range of glass transition temperatures (Tg = −51° (5e) to 97 °C (5k)) and the materials with long chain (OC12 (5f) or OC18 (5g)) alkoxy groups crystallize and exhibit melt transitions (Tm) at −30 and +32 °C, respectively. Wide-angle X-ray scattering studies of 5g suggest a lamellar structure with interdigitated side groups. Cyclic voltammetry studies of the selected poly(ferrocenylsilanes) 5a and 5i show the characteristic two-wave pattern for poly(ferrocenes) with interacting iron atoms with a redox coupling ΔE = ca. 0.22 V.