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Alkyl Effects on the Chain Initiation Efficiency of Olefin Polymerization by Cationic Half-Sandwich Scandium Catalysts: A DFT Study

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journal contribution
posted on 16.03.2016, 18:03 by Xiaohui Kang, Guangli Zhou, Xingbao Wang, Jingping Qu, Zhaomin Hou, Yi Luo
The effect of alkyls on the chain initiation efficiency of ethylene, propene, 1-hexene, styrene, butadiene, and isoprene polymerizations catalyzed by the half-sandwich cationic rare-earth-metal alkyl complexes [(η5-C5Me5)­ScR]+ (R = CH2SiMe3, 1; R = o-CH2C6H4NMe2, 2; R = η3-C3H5, 3) has been studied by using a DFT approach. It has been found that 2 with the largest sterically demanding aminobenzyl group results in the lowest initiation efficiency and thus longest induction period among the three catalysts investigated. In contrast, 1 with CH2SiMe3 displays the best chain initiation ability, and 3 with η3-allyl gives moderate chain initiation activity, mainly due to the most stable resulting coordination complex. Species 1 and 3 have better regioselectivity in the chain initiation of styrene polymerization than species 2. In addition, species 1′ ([(η5-C5Me5)­Sc­(CH2SiMe3)­THF]+) with a THF ligand has better chain initiation efficiency in styrene and isoprene polymerizations than species 2 but is reasonably worse than the analogue 1 without a THF ligand.