Catalytic olefin ougomerization and polymerization with cationic group IV metal complexes [Cp2∗MMe(THT)]+[BPh4]−, M = Ti, Zr and Hf

Diagonal Relationship among Organometallic Transition-Metal Complexes

“…In contrast to Kaminsky’s catalyst system Cp 2 ZrMe 2 /MAO, sterically crowded metallocene catalysts such as Cp* 2 ZrCl 2 /MAO and Cp* 2 HfCl 2 /MAO, as well as cationic catalysts such as [Cp* 2 MMe­(THT)]­[B­(C 6 F 5 ) 4 ] ( 22 , M = Zr, Hf), all active for propylene oligomerizations, favor β-methyl elimination over β-hydrogen elimination in the chain termination (eq ). ,− In contrast, as mentioned above, (C 5 H 4 R) 2 Ti­(CH 2 CMe 3 ) 2 ( 23 ; R = H, Me) normally undergoes α-H abstraction to give the corresponding alkylidene species . No experimental data are available, however, to support β-alkyl elimination for tantalum complexes: isolated isobutyl and neopentyl complexes bearing a Cp*Ta­(η 3 -1,3-diazaallyl) fragment were thermally stable toward β-hydrogen and β-methyl eliminations …”

Oligomerization of Monoolefins by Homogeneous Catalysts

“…In 1990 Teuben et al [27] reported that ionic group 4 complexes [Cp* 2 MMe(THT)] + (BPh 4 ) -(M = Zr, Hf, THT = tetrahydrothiophene) oligomerize propene and that the hafnium compound gives mainly one dimer (4-methyl-1-pentene: 72%) and one trimer (4,6-dimethyl-l-heptene: 24%). 3,3,3 Trideuteropropene was used to demonstrate that β-Me elimination is the dominant termination (Scheme 6).…”

Ethylene-Bridged Multi-Substituted Indenyl-Fluorenyl Zirconocene and Hafnocene Complexes: Synthesis, Structure and Catalytic Behavior for Propylene Selective Oligomerization

“…20 世纪 80 年代, Watson 等 [13] 在研究二(五甲基环戊 二烯基)稀土金属配合物催化丙烯聚合反应时, 首次发 现了金属中心 β-位 C-Me 键的活化现象, 吸引了相关 学者的深入研究. 随后, Teuben 等 [14,15] 和 Resconi 等 [16] 指出, 茂金属催化剂配体结构上特定位置的位阻环境对 β-H 消除反应过渡态的形成具有一定的抑制作用, 迫使 β-Me 取向于金属的最低未占分子轨道(LUMO)轨道, 从 而有效促进选择性 β-Me 消除反应的发生. 近年来, 人 们为了获得不同链长的烯丙基封端聚合产物, 导向选择 性 β-Me 消除的茂金属催化剂成了研究热点 [1,9,[17][18][19][20][21][22][23][24] , 然 而至今为止兼具 β-Me 消除选择性和丙烯齐聚性能的催 化 剂 报 道 仍 然 非 常 罕 见 .…”