Activation of enamido zirconium complexes for olffin polymerization: electrophilic addition versus electrophilic abstraction reaction

摘要

Homogeneous transition metal complexes for olefin polymerization are traditionally activated by electrophilic abstraction reaction by Lewis acids (eq 1). The activated complex is an ion-paired complex consisted of cation of transition metal and bulky non-coordinating anion. The pre-activated complex requires two alkyls or halides. One of them is abstracted by the Lewis acid and monomer inserts into the remaining metal-alkyl bond. Recently, some different activation reactions have been reported. Chen, et al. have reported that group 4 complexes bearing only one alkyl or halide can serve as efficient catalysts for olefin polymerization. They proposed a bimetallic mechanism resembling that originally proposed by Natta and Mazzanti (eq . 2). Bazan et al. and I have shown that nickel complexes containing carboxylato, carboxamidato, or enamido ligand can be activated by electrophilic addition reaction of Lewis acid. In those cases, the Lewis acid is added to the functional group to afford zwitterionic active complexes (eq. 3). Herein, we disclose that the novel activation reaction can be expanded to group 4 transition metal complexes. In these cases, it is characteristic that the pre-activated complexes have only one alkyl or halide.