乙烯选择性三聚/四聚铬系催化剂及其齐聚机理研究进展

线性α-烯烃是一类重要的有机化工原料和中间体，其下游市场包括聚乙烯、合成润滑油、表面活性剂等，其中C4~C8 组分的消费量占全球线性α-烯烃消费量的一半以上。采用1-己烯和1-辛烯作为共聚单体生产的线性低密度聚乙烯（LLDPE）和高密度聚乙烯（HDPE）产品具有优异的性能，被广泛用于薄膜、管材等领域。为了提高原子经济性，学术界和工业界一直致力于乙烯选择性三聚/四聚催化剂的设计与开发，而铬系催化剂是其中研究最广泛、最深入的体系。本文从配体、铬源、助催化剂、反应条件等方面综述了典型的铬系乙烯选择性三聚/四聚催化体系，包括雪佛龙菲利普斯乙烯三聚催化体系，Cr/PNP催化体系，以及其他N、P、Si配体等催化体系。在本文第二部分综述了乙烯选择性齐聚的相关机理提案，包括经典的Cossee-Arlman机理、单核金属环机理、双核金属环机理、双配位机理、及其他机理提案。

Selective Ethylene Tri-/tetramerization Catalyzed by Chromium-Based Catalysts and Oligomerization Mechanism

Linear alpha olefins are important chemical raw materials and intermediates, which are used in the production of polyethylene, synthetic lubricants, surfactants, etc. 1-Hexene and 1-octene are used as co-monomers to enhance the performance of linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE), which are widely used in the production of films, tubes, and other high-grade materials. About half of linear alpha olefins (C4~C8) are consumed by polyethylene manufacturers. Therefore, both academia and industry have long been devoting to develop effective catalysts for the selective oligomerization of ethylene into 1-hexene and 1-octene. Chromium catalysts are believed to be advantageous compared to other catalysts. In this review, the chromium-based catalysts with excellent catalytic performance for ethylene tri-/tetramerization are summarized, including the Phillips catalyst system for ethylene trimerization, the well-studied Cr/PNP catalysts for ethylene tri-/tetramerization, and other catalysts baring N-, P-, Si-based ligands. The catalyst development can be accelerated trough mechanistic understanding, including the linear Cossee-Arlman mechanism, the mononuclear metallacycle mechanism, the binuclear metallacycle mechanism, the double-coordination mechanism, and other mechanisms. With the mechanistic understandings on the chromium active oxidation states, the spin multiplicity of the catalyst systems, the electronic and steric effects of the ligands, the multiple conformers of the key intermediates, and other crucial factors, this catalyst system will surely become more and more mature through close collaboration between industrial and academia, and will finally be realized in industrial application for mass production of alpha olefins with tunable high selectivity.