Preparation and Crystal Structure of Bis(tert-butyltetramethylcyclopentadienyl)dichlorotitanium

[TiCl2(η5-C5Me4t-Bu)2] (1) was prepared by the reaction of [TiCl3(thf)3] with 2 equivalents of Li(η5-C5Me4t-Bu) (made by adding BuLi to a 1.33 molar excess of a mixture of tert-butyltetramethylcyclopentadiene isomers in THF) and subsequent oxidation of the Ti(III) intermediate to 1 by adding aqueous HCl. Neglecting the presence of cyclopentadiene isomers not forming the cyclopentadienide anion in the isomer mixture used for the synthesis of 1 resulted in the formation of hydrolytic product [{TiCl2(η5-C5Me4t-Bu)}2(μ-O)] (2) and a considerable decrease of yield of 1. The half sandwich complex [TiCl3(η5-C5Me4t-Bu)] (3) was obtained by synproportionation of 1 and TiCl4. Crystal structures of 1, 2, and 3 were determined. The electronic absorption spectra of 1 and 3 indicate a stronger electron-donor effect of tert-butyl group compared with methyl group.

Synthesis of Trichloro(η5-alkenyltetramethylcyclopentadienyl)titanium(IV) Complexes and Their Activity in Styrene Polymerization

Fully substituted trichloro(η5-cyclopentadienyl)titanium(IV) complexes with pendant alkenyl groups, [TiCl3(η5-C5Me4R)] (R = CH(Me)CH=CH2 (3a), (CH2)2CH=CH2 (3b), and (CH2)3CH=CH2 (3c)), were synthesized by the reaction of the corresponding trimethylsilyl or trimethylstannyl substituted cyclopentadienes C5Me4R(EMe3), where E = Si or Sn, with TiCl4. In all cases, the pendant double bonds did not exhibit any interaction with the titanium atoms as indicated by 1H, 13C NMR or IR spectra as well as by the solid-state structure of 3c. The catalytic systems prepared by mixing complexes 3a-3c, [TiCl3(η5-C5Me5)], [TiCl3(η5-C5H5)], and similar complexes with R = butyl (4), phenyl (5), 4-fluorophenyl (6) with methylalumoxane (MAO) at the molar ratio Al/Ti = 500 catalyzed polymerization of styrene to syndiotactic polystyrene. Their polymerization activities increase in the order: [TiCl3(η5-C5Me5)] < 3a < 3b < 3c < 4 < 5 < 6 < [TiCl3(η5-C5H5)], while the molecular weights (Mw) of syndiotactic polystyrene grow in the order: [TiCl3(η5-C5H5)] < 3a <3b < 4 ≈ 6 < [TiCl3(η5-C5Me5)] < 3c ≈ 5 (maximum Mw ca 3.0 · 105). A comparison of the results for the catalytic systems based on 4 with those derived from 3a-3c points to a rather weak competition of the pendant double bonds with monomer for a cationic Ti(III) catalytic centre.