1, 5-Naphthyl-linked bis(imino)pyridines as binucleating scaffolds for dicobalt ethylene oligo-/polymerization catalysts: exploring temperature and steric effects. Issue 23 (17th May 2019)

• Record Type: Journal Article
• Authors: Chen, Qiang; Suo, Hongyi; Zhang, Wenjuan; Zhang, Randi; Solan, Gregory A.; Liang, Tongling; Sun, Wen-Hua
• Is Part Of: Dalton transactions. Volume 48:Issue 23(2019)
• Page Start: 8264
• Page End: 8278
• Publication Date: 2019-05-17
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c9dt01235d
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : The title dinuclear Co complexes showed high activity for ethylene oligo-/polymerization with the run temperature having an unexpected effect on the PE to oligomer ratio. Abstract : Six examples of dinuclear bis(imino)pyridine-cobalt(ii ) complexes, [1, 5-{2-(CMeN)-6-(CMeN(2, 6-R 1 2 -4-R 2 -C6 H2 ))C5 H3 N}2 (C10 H6 )]Co2 Cl4 (R 1 = Me, R 2 = HCo1 ; R 1 = Et, R 2 = HCo2 ; R 1 = i Pr, R 2 = HCo3 ; R 1 = Me, R 2 = MeCo4 ; R 1 = Et, R 2 = MeCo5 ; R 1 = CHPh2, R 2 = MeCo6 ), have been prepared from the corresponding bis(tridentate) compartmental ligands (L1–L6 ) in reasonable yields. The molecular structures ofCo3 andCo5 revealed two N, N, N -cobalt dichloride units to adopt anti -positions about the 1, 5-naphthyl linking unit, with each cobalt center exhibiting a distorted trigonal bipyramidal geometry. On activation with either MAO or MMAO, Co1–Co6 were shown to promote both polymerization and oligomerization of ethylene with high overall activities (up to 1.03 × 10 7 gPE per·mol(Co) per·h forCo1 /MAO at 70 °C). Curiously, on increasing the reaction temperature a larger proportion of polymer was noted, while at lower temperature an enhanced selectivity for oligomer was seen. In general, the oligomeric products displayed Schulz–Flory distributions with high selectivities for α-olefins (>99%). On the other hand, the highly linear polymers displayed narrow dispersities and comprised both fully saturated and unsaturated chain ends with the vinyl content (–CHCH2 ) found to rise with the reaction temperature. By modulating the steric hindrance exerted by the ortho -R 1 substituents in the precatalyst, polyethylenes displaying a remarkably broad range of molecular weights could be obtained [from 4.52 kg mol −1 (R 1 = Me) to 246.7 kg mol −1 (R 1 = CHPh2 )].