Synthesis, characterization and styrene polymerization behavior of alkoxysilyl-substituted monocyclopentadienyltitanium(IV) complexes

Abstract

Trimethylsilylcyclopentadienes bearing alkoxysilyl functionality, C5H4(SiMe3)(SiMe2OR), where R is Me (2), i-Pr (3) and t-Bu (4), were prepared and characterized. Methoxy derivative 2 reacts with TiCl4 giving unstable [Ti(η5-C5H4SiMe2OMe)Cl3] (5), which is slowly transformed to chlorosilyl complex [Ti(η5-C5H4SiMe2Cl)Cl3] (6) and a mixture of cyclopentadienyltitanium(IV) methoxides on heating. Fully alkoxylated derivatives of the type [Ti(η5-C5H4SiMe2OR)(OR)3] [R = Me (7), i-Pr (8), t-Bu (9)] and {Ti[η5-C5H4SiMe(OMe)2](OMe)3} (10), were synthesized in low-to-moderate yields from respective chlorosilylcyclopentadienyltitanium trichlorides. All prepared alkoxysilyl compounds were characterized by spectroscopic techniques including 29Si NMR. Polymerization activity of 7–10 in the presence of methylaluminoxane was determined and compared with [TiCp(OMe)3] and corresponding trimethylsilyl-substituted compounds [Ti(η5-C5H4SiMe3)(OR)3], where R is Me, i-Pr and t-Bu. The highest conversion of styrene has been observed in systems based on [Ti(η5-C5H4SiMe3)(OMe)3], [TiCp(OMe)3] and [Ti(η5-C5H4SiMe3)(OBut)3], respectively. The new alkoxysilyl compounds 7–10 have significantly lower activity of 500–1800 kg of polystyrene/(mol Ti mol styrene h). All prepared polystyrenes showed both high melting point and high degree of syndiotacticity as determined by DSC and NMR measurements.