| Abstract
| - Addition of [Ph3C][B(C6F5)4] to [MesNpy]Hf(i-Bu)2 (1a; [MesNpy]2- = [H3CC(2-C5H4N)(CH2N-2,4,6-Me3C6H2)2]2-) yields {[MesNpy]Hf(i-Bu)}[B(C6F5)4] (2a) quantitatively. Compound 2a decomposes in a first-order manner at 0 °C in C6D5Br with kd = 9.2 × 10-6 s-1.The polymerization of 1-hexene by 2a at 0 °C in C6D5Br was found to follow first-orderkinetics with a kp = 0.10(1) M-1 s-1. The polymerization is well-behaved up to 10 °C withΔH⧧ = 10.82 kcal mol-1 and ΔS⧧ = −23.01 cal mol-1 K-1 (at [Hf] = 1 M). Up to 600 equiv of1-hexene were polymerized by 2a in chlorobenzene to give atactic poly[1-hexene] with theexpected Mn values and polydispersities between 1.02 and 1.05. Compound 1a could beactivated with B(C6F5)3 to yield {[MesNpy]Hf(CH2CHMe2)}[HB(C6F5)3] (2a‘), which willpolymerize 1-hexene in C6D5Br at 0 °C with kp = 0.048(1) M-1 s-1 and in toluene with kp =0.0111(3) M-1 s-1. Well-behaved inhibitors for 1-hexene polymerization include diisopropylether, hexyltrimethylsilyl ether, triethylamine, and tributylamine, but not diphenyl etheror dimethylaniline, both of which undergo CH activation. Activation of [MesNpy]Zr(i-Bu)2(1b) with [Ph3C][B(C6F5)4] in C6D5Br gave {[MesNpy]Zr(i-Bu)}[B(C6F5)4] (2b), whichdecomposed at 0 °C by β-hydride elimination in a first-order manner with kd = 8.3 × 10-6s-1. Polymerization of 100 equiv of 1-hexene by 2b appeared to be well-behaved attemperatures up to 10 °C (ΔH⧧ = 8.08 kcal mol-1 and ΔS⧧ = −33.34 cal mol-1 K-1 for [Zr]= 1 M), although sensitivity of 1b to light limited reproducibility in general. Activation of[MesNpy]ZrMe2 (4) with [Ph3C][B(C6F5)4] resulted in formation of primarily catalyticallyinactive {[MesNpy]2Zr2Me3}[B(C6F5)4]. However, ∼10% of the theoretical amount of{[MesNpy]ZrMe}[B(C6F5)4] is not trapped by [MesNpy]ZrMe2 and therefore is available toinitiate polymerization of 1-hexene slowly at room temperature. Bulk polymerization resultsobtained for this system support the assertion that only ∼10% of the added metal centersare active for polymerization. Activation of [MesNpy]HfMe2 with [Ph3C][B(C6F5)4] also resultsin formation of inactive {[MesNpy]2Hf2Me3}[B(C6F5)4].
- Polymerization of 1-hexene with {[MesNpy]Hf(i-Bu)}[B(C6F5)4] as the initiator at 0 °C in bromobenzene or chlorobenzene is well-behaved and yields atactic poly(1-hexene) samples whose molecular weights correspond to those expected for a perfectly living system. Activation of [MesNpy]HfMe2 (4) with [Ph3C][B(C6F4)4] resulted in formation largely of catalytically inactive {[MesNpy]2Hf2Me3}[B(C6F5)4].
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