A series of imine/phosphine-oxide ligands was synthesized and characterized. These ligands are easily prepared in a modular fashion, with positions that are independently tunable. The corresponding nickel allyl complexes were synthesized and serve as single-component catalysts for the homopolymerization of ethylene. It is generally believed that sterically bulky substituents lead to high polymer molecular weights during olefin polymerization. In this system, however, catalysts bearing the sterically bulky dibenzhydryl substituent afforded polyethylenes with much lower molecular weights than those bearing the sterically unhindered isopropyl substituent. Based on control experiments, theoretical calculations, and literature evidence, we propose that electronic effects override steric effects and play dominant roles in this nickel system. Efficient copolymerizations of ethylene with methyl 10-undecenoate and 6-chloro-1-hexene were also facilitated by this system without the need for any cocatalyst or protecting agent.

合成并表征了一系列的亚胺/膦氧化物配体。这些配体易于以模块化方式制备，其位置可独立调节。合成了相应的镍烯丙基配合物，并用作乙烯均聚的单组分催化剂。通常认为，空间大的取代基在烯烃聚合过程中导致高的聚合物分子量。然而，在该体系中，带有空间上庞大的二苯甲酰基取代基的催化剂所提供的聚乙烯的分子量比带有空间上不受阻碍的异丙基取代基的聚乙烯的分子量低得多。基于控制实验，理论计算和文献证据，我们建议电子效应优先于空间效应，并在该镍体系中起主导作用。