Influence of intramolecular π-π and H-bonding interactions on pyrazolylimine nickel-catalyzed ethylene polymerization and co-polymerization

Designing new catalysts through structural modification is a permanent dimension in catalysis. In this scenario, the limitations of pyrazolylimine, concerning their low thermal stability and providing the polymer with low molecular weight, have been improved. For this purpose, sterically hindered N -(2,6-dibenzhydryl-4-methylphenyl)benzimidoyl chloride was selected to link 3,5-Me and -Ph substituted pyrazoles, inspired by the role of bulky dibenzhydryl groups in α-diimine and other catalytic systems. From crystallographic analysis, it was noticed that after the formation of catalysts, the phenyl of dibenzhydryl and benzimidoyl orient themselves in such a way to develop proper off-set intramolecular π-π interactions. Likewise, the counter dibenzhydryl groups shield the metal center much closely, so that distance of hydrogen attached with methine carbon to bromide was recorded to be 2.634 Å, which confirms the intramolecular H-bond. The effectiveness of this combination in these catalysts is illustrated by their higher thermal stability along with a 40 times higher molecular weight than the previously reported pyrazolylimine catalysts. Moreover, co-polymerization was also done with considerable incorporation of methyl 10-undecenoate. Pyrazolylimine-based nickel catalysts bearing intramolecular π-π and H-bonding interactions show high activity, thermal stability, and Mn of polyethylene.