Pentamethylcyclopentadienylmethyltitanium Silsesquioxanes and Their Zwitterionic Complexes with Tris(pentafluorophenyl)borane

Reaction of [(η5-C5Me5)TiMe3] with [(c-C5H9)7Si8O12(OH)] (SIPOSS) or [(c-C5H9)7Si7O9(OSiMe3)(OH)2)] (DIPOSS′) affords stoichiometrically the half-sandwich titanium-disiloxy-methyl complexes [(η5-C5Me5){(c-C5H9)7Si8O12O}2TiMe] (1) and [(η5-C5Me5){(c-C5H9)7Si7O9(OSiMe3)O2}TiMe] (2), respectively. Compound 2 consists of the two stereoisomers possessing the (η5-C5Me5) ligand and OSiMe3 group in syn- (2a) and anti-position (2b). The more abundant 2a (2a/2b ≈ 2:1) was isolated by fractional crystallization. Compounds 1 and 2a reacted rapidly with B(C6F5)3 to give zwitterionic complexes [(η5-C5Me5){(c-C5H9)7Si8O12O}2Ti](+)[(μ-Me)B(C6F5)3](−) (3) and syn-[(η5-C5Me5){(c-C5H9)7Si7O9(OSiMe3)O2}Ti](+)[(μ-Me)B(C6F5)3](−) (4a), respectively. Infrared spectra proved that 3 and 4a were thermally stable in the solid state, and the structure of 4a was determined by X-ray single-crystal analysis. In contrast, 1H, 13C, and 19F NMR spectra of 3 in toluene C7D8 revealed that it was completely dissociated into initial components at 25 °C; however, the features of 3 were dominating already at −35 °C. On the other hand, 4a was dissociated only slightly at 25 °C. Stable ionic complexes 7 and 8 were prepared by reacting [PhNHMe2]+[B(C6F5)4]− with 1 and 2, respectively. Both 7 and 8 contained the molecule PhNMe2 coordinated to the titanium cation, and 8 consisted of the syn- and anti-isomers 8a and 8b in abundances found for 2a/2b. Analogous reaction of 1 and 2 with [Ph3C]+[B(C6F5)4]− afforded impure ionic complexes 9 and 10. When dissolved in the presence of PhNMe2, the amine coordinated to the titanium cations, thus reproducing complexes 7 and 8a/8b, identified by 1H NMR spectra. All compounds 1−10 were inactive in polymerization of styrene to syndiotactic polymer. A low activity was achieved by adding of 2 equiv of AlMe3 to 3 or 4.