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

Abstract

Titanium complexes of silicon-bridged cyclopentadienyl−phenoxy ligands modified with fused-thiophene, R 2 Si(L)(3- t Bu-5-Me-2-C 6 H 2 O)TiCl 2 { 5: R = Me; L = 6- L 1; L 1 = 2,4,5-Me 3 -cyclopenta[2,3- b ]thiophenyl, 6: R = Et; L = 6- L 1, 9a: R = Me; L = 4- L 2; L 2 = 2,5-Me 2 -cyclopenta[3,2- b ]thiophenyl, 10a: R = Et; L = 4- L 2, 16: R = Me; L = 7- L 3; L 3 = 2,5-Me 2 -cyclopenta[1,2- b:4,3- b ′]dithiophenyl, 17: R = Et; L = 7- L 3, 18: R = Et; L = 7- L 4; L 4 = cyclopenta[1,2- b:4,3- b ′]dithiophenyl, 19: R = Et; L = 4- L 5; L 5 = 2,6-Me 2 -cyclopenta[2,1- b:3,4- b ′]dithiophenyl, 20: R = Et; L = 4- L 6; L 6 = cyclopenta[2,1- b:3,4- b ′]dithiophenyl}, were prepared by treating TiCl 4 with the dilithium salts generated by reaction of the corresponding ligands ( 3, 4, 7, 8, and 11 − 15 ) with n BuLi in the presence of Et 3 N in toluene. In the ligand synthesis, the use of L 2 -H afforded R 2 Si(L-H)[2-(OCH 2 CH═CH 2 )-3- t Bu-5-Me-C 6 H 2 ] ( 7a: R = Me; L = 4- L 2, 8a: R = Et; L = 4- L 2 ) along with a small amount of the isomer R 2 Si(L-H)[2-(OCH 2 CH═CH 2 )-3- t Bu-5-Me-C 6 H 2 ] ( 7b: R = Me; L = 6- L 2, 8b: R = Et; L = 6- L 2 ), 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 η 5 -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 η 3 -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 i Bu 3 Al/[Me 2 NHPh][B(C 6 F 5 ) 4 ] and afforded higher molecular weight copolymer than the parent tetramethyl-substituted cyclopentadienyl complex Me 2 Si(η 5 -C 5 Me 4 )(3- t Bu-5-Me-2-C 6 H 2 O)TiCl 2 ( 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.