[1-(2-Phenylethyl)-2,3,4,5-tetramethylcyclopentadienyl]- titanium Compounds. Synthesis and Their Use for the Syndiospecific Polymerization of Styrene

A series of monocyclopentadienyltitanium complexes containing the 1-(2-phenylethyl)-2,3,4,5-tetramethylcyclopentadienyl ligand (C5Me4CH2CH2Ph) have been synthesized and characterized. The reaction of C5Me4(SiMe3)CH2CH2Ph (2) with TiCl4 was used to synthesized the trichloro complex (C5Me4CH2CH2Ph)TiCl3 (3), the molecular structure of which was confirmed by an X-ray diffraction study. Compound 3 was further converted into (C5Me4CH2CH2Ph)TiMe3 (4). Reaction of the latter with 1 equiv of [Ph3C][B(C6F5)4] was almost quantitative to give the “cationic” compound [(C5Me4CH2CH2Ph)TiMe2]+[B(C6F5)4]- (5). Complex 5 was thermally unstable in solution and very moisture sensitive. Compound 4 was readily hydrolyzed to [(C5Me4CH2CH2Ph)TiMe2]2(μ-O) (6) upon recrystallization in wet pentane. Structural data indicate intramolecular coordination of the phenyl group to titanium in compound 5, whereas there are no such indications for 3, 4, or 6. The catalytic performance for styrene polymerization of 3 activated with methylal...