Ethylene oligomerization/polymerization over a series of iminopyridyl Ni(II) bimetallic catalysts modulated electronically and sterically

A series of sterically and electronically modulated iminopyridyl Ni(II) bimetallic catalysts of the general formula [(2,6-C5H3NX)–CN–(Z)–NC–(2,6-C5H3NX)][NiBr2]2 {Z = (2,6-C6H2R2)2CH(4-C6H4Y); R = Me, Et, iPr; Y = H, NO2, OCH3, X = H, Me, Ph} have been synthesized. When activated with methylaluminoxane or common alkyl aluminums such as ethyl aluminum sesquichloride (EASC), all catalysts oligomerize/polymerize ethylene with activities exceeding 106 g-product/(mol-Ni h bar) at 30 °C to yield C4 as a major product. Among the cocatalysts used, EASC records the best activity. The effect of electronic modification of the complexes on catalytic activity was studied by using UV–vis spectroscopy and cyclic voltammetry. The cooperative effect due to two metal centers of bimetallic complexes was evidenced by comparing the molecular weight of polymer and the 13C NMR spectra of poly(1-hexene) obtained by its monometallic analogue.

Graphical abstractA series of sterically and electronically modulated iminopyridyl Ni(II) bimetallic catalysts showed activity exceeding 106 g-product/mol-Ni h bar at 30 °C to yield C4 as a major product when activated with ethyl aluminium sesquichloride. The cooperative effect of iminopyridyl bimetallic nickel catalyst was evidenced by comparing the physical properties and microstructures of polymers obtained by its monometallic analogue.Figure optionsDownload full-size imageDownload as PowerPoint slide