Prospects and crucial problems in oligomerization and polymerization with iron and cobalt complex catalysts

The discovery of highly active 2,6-bis(imino)pyridyl iron and cobalt complexes provided a milestone of late-transition metal catalysts for ethylene oligomerization and polymerization with being currently investigated for the scale-up process. The crucial problems are remaining in the catalytic systems: the catalytic systems targeting ethylene polymerization produce more oligomers at elevated reaction temperatures, however, there is a recognizable amount of high-molecular-weight polyethylene remained in the modified catalytic system for the oligomerization process. Beyond the modification of bis(imino)pyridyl metal complexes, several alternative procatalysts' models have been developed in our group. This review highlighted the achievements in exploring new iron and cobalt complexes with tridentate NNN ligands as procatalysts for ethylene oligomerization and polymerization.