The effect of the amido substituent on polymer molecular weight in propene homopolymerisation by titanium cyclopentadienyl‐amide catalysts

Sinnema, Piet-Jan; Hessen, Bart; Teuben, Jan H.

doi:10.1002/1521-3927(20000601)21:9<562::aid-marc562>3.0.co;2-#

Cited by 18 publications

(12 citation statements)

References 5 publications

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“…The low predicted value of −5.5 kcal/mol for BHE at (C 6 F 5 NCHC 6 H 4 O) 2 Ti is not compatible with the high MW obtainable with FI catalysts, although the lack of steric hindrance at the phenol moiety of our model system might be a factor here. High molecular weights are correctly predicted for Cp*SiMe 2 N t BuTi and Cp*CH 2 CH 2 N t BuTi systems.…”

Section: Resultsmentioning

confidence: 89%

Variability of Chain Transfer to Monomer Step in Olefin Polymerization

Talarico

Budzelaar

2008

Organometallics

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Computational studies of a variety of polymerization catalyst models have revealed an unexpected fluidity in chain termination mechanisms. For many early transition metal olefin polymerization catalysts two distinct transition states exist for β-hydrogen transfer to monomer, which differ mainly in the M−H distance and CMC angle. The transition state for the “classical” (BHTA) path resembles a metal hydride−bis(olefin) complex, whereas the alternative BHTB path involves direct transfer of an alkyl β-hydrogen to a coordinated olefin without any metal−hydride interaction. The two transition states are separated by a second-order saddle point that is just a few kcal/mol above the highest of the two transition states, indicating a flat potential-energy surface between the two paths. Of the group IV metals, Zr (in contrast to Ti and Hf) appears to have an intrinsic preference for the “classical” BHTA path. Increasing the amount of space around the metal (e.g., in lanthanocenes) changes BHTA into a two-step path (BHTC), showing two β-hydride elimination transition states around a hydride−bis(olefin) complex local minimum. Decreasing the amount of space by using sterically demanding ligands results in a shift toward the “new” BHTB path. However, β-hydrogen elimination becomes more favorable at the same time, and our results suggest that for most early transition metal catalysts (typically 14-e metal alkyls) either BHTA or β-hydrogen elimination will be the dominant chain-transfer pathway, whereas BHTB may be relevant for some Hf complexes of intermediate crowding. The BHTB path is expected to be more important for systems that are less unsaturated (16-e transition metal alkyls; 6-e main-group metal alkyls) and also for “hetero-olefin” derivatives (alkoxides, amides), where β-hydrogen elimination is strongly endothermic.

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Section: Resultsmentioning

confidence: 89%

Variability of Chain Transfer to Monomer Step in Olefin Polymerization

Talarico

Budzelaar

2008

Organometallics

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“…Therefore, the ligands of title procatalysts and model catalyst A occupy more space around the active titanium center. It is supposed that the chain transfer process of the half-titanocene catalyst requires more space in the coordination sphere of the titanium than the olefin insertion state does. , So the title catalysts produce polyethylenes with higher molecular weights than catalysts A and B . Due to bulky substituents, the catalysts C1 and C2 produce polyethylenes with higher molecular weight than catalyst C5 , containing ligands with less steric influence.…”

Section: Resultsmentioning

confidence: 99%

Syntheses, Characterization, and the Ethylene (Co-)Polymerization Screening of 2-Benzimidazolyl-N-phenylquinoline-8-carboxamide Half-Titanocene Chlorides

et al. 2010

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A series of 2-benzimidazolyl-N-phenylquinoline-8-carboxamide half-titanocene chlorides, CpTiLCl (C1−C6: Cp = η5-C5H5; L = 2-(1H-benzo[d]imidazol-2-yl)-N-(2,6-R1-4-R2-phenyl)quinoline-8-carboxamide derivatives; C1: R1 = i-Pr, R2 = H; C2: R1 = Et, R2 = H; C3: R1 = Me, R2 = H; C4: R1 = Me, R2 = Me; C5: R1 = H, R2 = H; C6: R1 = F, R2 = H), have been synthesized by the stoichiometric reaction of half-titanocene trichlorides with the corresponding potassium 2-benzimidazolyl-N-phenylquinoline-8-carboxamide. All complexes are fully characterized by elemental and NMR analyses, as well as single-crystal X-ray diffraction for complexes C1, C2, and C6. In addition, the oxo-bridged dinuclear complex C7 was separated from the solution of C6 in air. These complexes, C1−C6, activated with methylaluminoxane (MAO), exhibit high catalytic activities toward both ethylene polymerization and copolymerization of ethylene with α-olefins. According to the catalytic system of C1/MAO, both elevating the reaction temperature and increasing the ratio of MAO to titanium precursor enhance the productivities; however, the molecular weights of the resultant polymers obtained decrease against their higher activities. Moreover, copolymerizations of ethylene with either 1-hexene or 1-octene effectively produce copolymers with incorporated comonomers of 2.0−5.0% mol.

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“…[20] Hessen et al investigated the effect of the amido substituent on propene polymerization using ethylene-bridged CpA titanium dichlorides and their dibenzyl derivatives combined with MAO and B(C 6 F 5 ) 3 , respectively, and found that the effects of the amido substituent on the productivity and molecular weight were dependent on the cocatalyst employed. [21] We have previously investigated propene polymerization with [g 3 :g 1 -tert-butyl(dimethylfluorenylsilyl)amido]-dimethyltitanium ([t-BuNSiMe 2 Flu]TiMe 2 ). We found that [t-BuNSiMe 2 Flu]TiMe 2 catalyzed the living polymerization of propene in a highly regiospecific manner at -50 or 0 8C when B(C 6 F 5 ) 3 or Me 3 Al-free MAO (dried and washed before use), respectively, were employed as cocatalyst, [22,23] while it produced low-molecular weight polypropene in high yields at 40 8C using MAO as cocatalyst because of the chain transfer by Me 3 Al in MAO.…”

Section: Introductionmentioning

confidence: 99%