Rotating Benzyl Substituent in ansa-Bis(indenyl)zirconocenes Controls Propene Polymerization

Abstract

A series of benzyl-substituted, dual-site ansa-metallocenes were synthesized and characterized. Their isolated rac-and meso-diastereomers were studied in propene polymerization after methylaluminoxane or borate activation. Catalysts' polymerization behavior were investigated in various polymerization conditions, and produced polypropenes (PPs) were characterized with NMR, GPC, and DSC. The rac-and meso-diastereomers of these unsymmetric catalysts bearing a SiMe 2 bridge produced PP with similar activity, tacticity, and molar mass. According to quantum chemical calculations, the benzyl group in the catalysts can rotate, having significant energy minima. The reason that the diastereomers produce PP with similar molar mass is linked to these local energy minima and is further discussed.

Accurate Prediction of Copolymerization Statistics in Molecular Olefin Polymerization Catalysis: The Role of Entropic, Electronic, and Steric Effects in Catalyst Comonomer Affinity

“…Rational modeling of a polymerization process can be a challenging task, due to the complexity of the reaction pool and the high accuracy that is needed for predictions to be useful. On the one hand, prediction of stereochemistry represents a particularly successful case for computational modeling. − On the other hand, many other catalyst properties are at least as important but are more difficult to rationalize. For instance, prediction of molecular weight capability works only in simple cases where the main termination process can be easily and unambiguously identified, − while prediction of catalyst activity (“productivity”) and catalyst decay (“catalyst mileage”) is greatly hampered by its strong dependence on reaction and activation conditions, − although some progress has been made recently. , …”

Synthesis and Characterization ofansa-Bis(3-chiral groupsubstituted indenyl) Zirconium Complexes

“…可能是由于配体结构 中单原子的亚甲基桥, 使得化合物 1a 的两个茚环相距 较近, 再加上 3-位(1S,2S,5R)-新孟基的存在, 使空间位 阻变大, 锆原子不能有效与茚环络合. 亚乙基桥联-二{3-[(1S,2S,5R)-新孟基]-1-茚基}二氯 化锆络合物的合成路线 [9,13] 络合物 2c 中 Zr 原子与两个茚基的五元环上 5 个碳 原子的键长、键角与文献中 meso-构型亚乙基桥联二茚 锆络合物报道类似 [14] , 说明 Zr 原子与两个茚基以 η 5 模 表 1 络合物 2c 的主要键长(Å)…”

“…[22,23] [22～26] . 另外, 该步反应的主要副产物为 只有一个溴被茚基取代的产物, 所以要严格控制 1,2-二 溴乙烷的用量, 不能过量, 否则导致一取代副产物增 加 [12,13,22,23] . [12,13,22,23] .…”

Group 4 Complexes Supported by Pyridine-2-Phenolate-6-Arylmethine Ligands: Spectroscopic and Structural Characterization and Olefin Polymerization Catalysis

“…With regards to the fluorinated [O,N,C]-Ti system, the ability to spectroscopically detect intramolecular C–H···F–C interactions is considered to be linked to their intrinsic rigidity, yet this may not be conducive to desirable (well-defined) reactivity . As revealed by our investigation of [O,N,C­(σ-naphthyl)]-Ti catalysts ( D ), including by DFT calculations, insertion of olefin into the Ti–C­(sp 2 ) bond is competitive with normal chain propagation to afford additional “olefin-assimilated” [Ti–C 2 H 4 –naphthyl] active species ( E ), leading to polymers with broad molecular weight distributions indicative of multisite behavior. , Motivated by these observations, we turned our attention to C­(sp 3 )-chelating auxiliaries and the development of the [O,N,C­(methine)] system ( F ): (i) the greater flexibility of the M–C­(sp 3 ) chelation [compared with M–C­(sp 2 )] and rotating aryl substituent in these catalysts would permit the formation of optimal structures during the polymerization and reduce activation energies, thereby improving catalytic performance, (ii) if sufficiently robust, the four-membered N,C-donor chelate ring would confer a relatively small bite angle to facilitate monomer binding and chain migration processes. More generally, the chelate ring size can stabilize or activate the catalytic species as well as enhance or hinder alternative reaction pathways such as olefin assimilation.…”