Ring-Opening Polymerization Behavior of ansa- and Spirocyclic ansa-Zirconocene Complexes

Attempts to develop a ring-opening polymerization (ROP) approach to polymeric zirconocene complexes are reported. A new silicon-bridged [1][1]zirconocenophane, (SiMe2)2(η5-C5H3)2Zr(NEt2)2 (3a), was synthesized by reaction of Zr(NEt2)4 with (C5H4)2(SiMe2)2 (4). Single-crystal X-ray diffraction revealed a highly tilted structure with an angle of 73.1(4)°, a significant increase over the untethered compound (η5-MeC5H4)2ZrCl2 (2), which possesses a tilt angle of 54.2°. This and the related compounds (SiMe2)(η5-C5H4)2MCl2 (1a, M = Ti; 1b, M = Zr) and (SiMe2)2(η5-C5H3)2ZrCl2 (3b) were tested for transition-metal catalyzed ROP behavior in the presence of Pt(0) catalysts but were found to be inactive. The novel spirocyclic silacyclobutane-bridged monomer (CH2)3Si(η5-C5H4)2ZrCl2 (7b) was prepared via a “fly trap” amine elimination reaction between cyclotrimethylenedicyclopentadienylsilane (8) and Zr(NMe2)4; this initially yielded (CH2)3Si(η5-C5H4)2Zr(NMe2)2 (7a), which was converted to 7b by reaction with a slight...