Titanium Complexes of Silicon-Bridged Cyclopentadienyl−Phenoxy Ligands Modified with Fused-Thiophene: Synthesis, Characterization, and Their Catalytic Performance in Copolymerization of Ethylene and 1-Hexene

Titanium complexes of silicon-bridged cyclopentadienyl−phenoxy ligands modified with fused-thiophene, R2Si(L)(3-tBu-5-Me-2-C6H2O)TiCl2 {5: R = Me; L = 6-L1; L1 = 2,4,5-Me3-cyclopenta[2,3-b]thiophenyl, 6: R = Et; L = 6-L1, 9a: R = Me; L = 4-L2; L2 = 2,5-Me2-cyclopenta[3,2-b]thiophenyl, 10a: R = Et; L = 4-L2, 16: R = Me; L = 7-L3; L3 = 2,5-Me2-cyclopenta[1,2-b:4,3-b′]dithiophenyl, 17: R = Et; L = 7-L3, 18: R = Et; L = 7-L4; L4 = cyclopenta[1,2-b:4,3-b′]dithiophenyl, 19: R = Et; L = 4-L5; L5 = 2,6-Me2-cyclopenta[2,1-b:3,4-b′]dithiophenyl, 20: R = Et; L = 4-L6; L6 = cyclopenta[2,1-b:3,4-b′]dithiophenyl}, were prepared by treating TiCl4 with the dilithium salts generated by reaction of the corresponding ligands (3, 4, 7, 8, and 11−15) with nBuLi in the presence of Et3N in toluene. In the ligand synthesis, the use of L2-H afforded R2Si(L-H)[2-(OCH2CHCH2)-3-tBu-5-Me-C6H2] (7a: R = Me; L = 4-L2, 8a: R = Et; L = 4-L2) along with a small amount of the isomer R2Si(L-H)[2-(OCH2CHCH2)-3-tBu-5-Me-C6H2] (7b: R = Me; L = 6-L2, 8b: R = Et; L = 6-L2), respectively. X-ray crystallographic studies of 6, 17, and 19 indicate that the cyclopentadienyl moiety of 6 with TFCp (TFCp = thiophene-fused cyclopentadienyl) is bound to the titanium atom in an η5-fashion, whereas the coordination of the moieties to the metal in 17 and 19 with DTFCp (DTFCp = dithiophene-fused cyclopentadienyl) contributes in somewhat of an η3-manner. The newly prepared complexes 5, 6, 9, 10, and 16−20 exhibited high catalytic activities for copolymerization of ethylene and 1-hexene in the presence of iBu3Al/[Me2NHPh][B(C6F5)4] and afforded higher molecular weight copolymer than the parent tetramethyl-substituted cyclopentadienyl complex Me2Si(η5-C5Me4)(3-tBu-5-Me-2-C6H2O)TiCl2 (1a). The complexes 6, 17, and 19 were thermally stable and exhibited high polymerization activities, even at 180 °C. Among tested complexes, the DTFCp complexes 17 and 19 at 180 °C showed very high activity and produced high molecular weight copolymers with good 1-hexene content.