Synthesis and Properties of Poly(ferrocenyldihydrosilane) Homopolymer and Random Copolymers

Abstract

The strained, silicon-bridged [l]ferrocenophane Fe(η-C 5 H 4 ) 2 SiH 2 (4) was prepared via the reaction of H 2 SiCl 2 with Fe(η-C 5 H 4 Li) 2 .TMEDA in ether at < -78°c. This species was analyzed by single-crystal X-ray diffraction and was found to possess a strained, ring-tilted structure similar to those of previously reported silicon-bridged [l]ferrocenophanes [tilt angle 19.1(1)°]. Thermal ring-opening polymerization of 4 afforded the poly(ferrocenylsilane) [Fe(η-C 5 H 4 ) 2 SiH 2 ] n (5), which was found to be insoluble in common organic solvents. Under the same conditions, mixtures of 4 and the dimethyl analog Fe(η-C 5 H 4 ) 2 SiMe 2 (1a) afforded soluble copolymers 7a-c, consisting of random ferrocenyldihydrosilane and ferrocenyldimethylsilane repeat units, as the first examples of poly(ferrocenylsilane) copolymers prepared via ring-opening polymerization. Repeat unit composition of the random copolymers could be controlled by manipulation of the monomer ratio and was readily assessed by l H NMR spectroscopy. TGA of 5 under N 2 at a heating rate of 10 °C/min found this material to be the most thermally stable to weight loss of all the poly(ferrocenylsilanes) yet studied with only 10% weight loss up to 600 °C and a ceramic yield of 63% at 1000 °C. Among copolymers 7a-c, thermal stability to weight loss increased with increasing ferrocenyldihydrosilane repeat unit content. The homopolymer 5 was found to be crystalline by wide-angle X-ray scattering, and a melting transition at 165 °C was detected by DSC. Glass transitions for the essentially amorphous copolymers were observed to fall between the T g of 18 °C observed for 5 and the T g of 33 °C reported for [Fe(η-C 5 H 4 ) 2 SiMe 2 ] n (2a).