Structural analysis of imino- and amino-pyridine ligands for Ni(II):Precatalysts for the polymerization of ethylene

Publication date: Available online 10 March 2018 Source:Journal of Organometallic Chemistry Author(s): Danielle M. Lovett, Laura M. Thierer, Earl E.P. Santos, Rachel L. Hardie, William G. Dougherty, Nicholas A. Piro, W. Scott Kassel, Brian M. Cromer, E. Bryan Coughlin, Deanna L. Zubris Imino- and amino-pyridine ligands are versatile scaffolds to probe how ligand sterics influence polymerization outcomes for nickel(II) ethylene polymerization catalysts. Six imino- and one amino-pyridine nickel(II) complexes with varied imino/amino-carbon substitution (R1 = methyl, ethyl, isopropyl or tert-butyl) were synthesized (1-7). Five of these complexes were analyzed crystallographically: dimeric {[2-[(2,6-Me2-C6H3)N=C(R1)]C5H4N]NiBr2}2 (R1 = Et 2; R1 = t-Bu 4), monomeric [2-[(2,6-Me2-C6H3)N=C(R1)]C5H4N]NiBr2NCCH3 (R1 = Me 5; R1 = t-Bu 6), and monomeric [2-[(2,6-Me2-C6H3)NHCH(t-Bu)]C5H4N]NiBr2 (7). Complexes 1-7 are competent ethylene polymerization precatalysts at 0°C, and tert-butyl substituted imino-pyridine precatalysts 4 and 6 and amino-pyridine precatalyst 7 display the best activity, highest polyethylene molecular weight, and narrowest dispersity values of series. 13C-NMR analyses of polyethylene samples reveal a lightly branched morphology with a modest amount of methyl branching; polymer T m values are consistent with this assessment. Ongoing work includes further exploration of precatalysts 4, 6, and 7 in attempt to maximize polyethylene molecul...

Source: Journal of Organometallic Chemistry - March 10, 2018 Category: Chemistry Source Type: research