Poly(ferrocenylmethylsilane): An Unsymmetrically Substituted, Atactic, but Semicrystalline Polymetallocene

Abstract

Polyferrocenylsilanes (PFSs) [Fe­(μ-C₅H₄)₂SiRR′]_<i>n</i> are generally atactic and amorphous when unsymmetrically substituted at silicon (R ≠ R′) but are often able to crystallize if the substitution is symmetrical (R = R′). In this paper we report detailed studies of the ring-opening polymerization (ROP) of [1]­methylsilaferrocenophane Fe­(μ-C₅H₄)₂SiMeH (<b>1</b>) by thermal, anionic and photolytic methods to yield an unsymmetrically substituted yet crystallizable poly­(ferrocenylmethylsilane) (<b>PFMS</b>) (R = Me, R′ = H) with Me and H substituents at silicon (designated <b>PFMS</b>_<b>T</b>, <b>PFMS</b>_<b>A</b>, and <b>PFMS</b>_<b>P</b>, respectively). The structures of the resulting polymers were shown to possess significant differences as revealed by MALDI–TOF mass spectroscopy experiments. For example, <b>PFMS</b>_<b>A</b> prepared using <i>n</i>-BuLi as an initiator was shown to contain cyclic contaminants whose formation indicated the existence of backbiting reactions during polymer chain growth. On the other hand, photolytic ROP of <b>1</b> using Na­[C₅H₅] as an initiator led only to the formation of linear material but was not a living process due to side reactions between the initiator (and presumably the propagating polymeric anions) and the Si–H groups in the monomer <b>1</b>. Transition metal-catalyzed ROP of <b>1</b> was also explored and, in contrast, was found to afford a hyperbranched and amorphous low molar mass polyferrocenylsilane (<b>4</b>), presumably also as a result of side reactions involving the Si–H groups in the monomer. High resolution ¹H and ¹³C NMR spectroscopic studies revealed that <b>PFMS</b>_<b>T</b>, <b>PFMS</b>_<b>A</b>, and <b>PFMS</b>_<b>P</b> were all atactic, irrespective of the polymerization route utilized. The crystallization of the samples was investigated by wide-angle X-ray scattering (WAXS), which showed a reflection corresponding to a <i>d</i>-spacing of 6.32 Å, by differential scanning calorimetry (DSC), which revealed melting endotherms in the range 106–139 °C, and by polarizing optical microscopy (POM)