293764-48-4Relevant academic research and scientific papers
Living polymerization of 1-hexene by cationic zirconium and hafnium complexes that contain a diamido/donor ligand of the type [H3 CC(2-C5H4N)(CH2 NMesityl)2]2-. A comparison of methyl and isobutyl initiators
Mehrkhodavandi, Parisa,Schrock, Richard R.,Pryor, Lara L.
, p. 4569 - 4583 (2003)
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-order kinetics with a kp = 0.10(1) M-1 s-1. The polymerization is well-behaved up to 10°C with ΔH? = 10.82 kcal mol-1 and ΔS? = -23.01 cal mol-1 K-1 (at [Hf] = 1 M). Up to 600 equiv of 1-hexene were polymerized by 2a in chlorobenzene to give atactic poly[1-hexene] with the expected Mn values and polydispersities between 1.02 and 1.05. Compound 1a could be activated with B(C6F5)3 to yield [MesNpy]Hf(CH2CHMe2)} [HB(C6F5)3] (2a′), which will polymerize 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 diisopropyl ether, hexyltrimethylsilyl ether, triethylamine, and tributylamine, but not diphenyl ether or 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), which decomposed at 0°C by β-hydride elimination in a first-order manner with kd = 8.3 × 10-6 s-1. Polymerization of 100 equiv of 1-hexene by 2b appeared to be well-behaved at temperatures 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 catalytically inactive {[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 to initiate polymerization of 1-hexene slowly at room temperature. Bulk polymerization results obtained for this system support the assertion that only ～10% of the added metal centers are active for polymerization. Activation of [MesNpy]HfMe2 with [Ph3C][B(C6F5)4] also results in formation of inactive {[MesNpy]2Hf2Me3}[B(C6F5) 4].
