Nickel complexes bearing substituted 2-(naphthylen-1-yl)iminopyridines as catalysts for the formation of highly branched unsaturated PE waxes

Abstract

A set of six 2-iminopyridine-nickel(II) complexes, [2-{C(Me)=NAr}C5H4N]NiCl2 (Ar = 1-C10H7Ni1, 2-Me-1-C10H6Ni2, 2-(CHMePh)-1-C10H6Ni3, 4-(NNC6H5)-1-C10H6Ni4, 4-(NNC6H4-4-Me)-1-C10H6Ni5, 4-(NNC6H4-4-F)-1-C10H6Ni6), all N-functionalized with naphthalen-1-yl or its substituted alkyl or aryldiazenyl derivatives, have been readily synthesized from their corresponding free N,N-ligand, L1 – L6. On crystallization of Ni3, the chloride-bridged trimetallic species, [(L3)3Ni3Cl6(OH2)], was identified as an aqua adduct by single crystal X-ray diffraction. When activated with either MAO or MMAO, high catalytic activity for ethylene polymerization was achieved using Ni1–Ni6 (up to 10.1 × 106 g (PE) mol−1 h−1 for Ni3/MAO), affording low molecular weight polyethylene (Mw range: 0.81–3.50 kg mol−1) with low melting temperature and narrow dispersity. 13C NMR spectroscopic analyses of these polyethylenic waxes revealed the formation of branched macromolecules with branching densities up to 69 per 1000 carbons. Further analysis revealed these polymers to contain predominantly methyl branches (%Me range: 7.8–9.0), with lower levels of longer chain branching and some branch-on branch structure (%sec-Bu range: 0.07–0.12%). Moreover, their 1H and 13C NMR spectra showed various levels of unsaturated functionality in the form of terminal and internal olefins.