1,5-Naphthyl-linked bis(imino)pyridines as binucleating scaffolds for dicobalt ethylene oligo-/polymerization catalysts: exploring temperature and steric effects

Qiang Chen; Hongyi Suo; Wenjuan Zhang; Randi Zhang; Gregory A Solan; Tongling Liang; Wen-Hua Sun

doi:10.1039/c9dt01235d

1,5-Naphthyl-linked bis(imino)pyridines as binucleating scaffolds for dicobalt ethylene oligo-/polymerization catalysts: exploring temperature and steric effects

Dalton Trans. 2019 Jun 21;48(23):8264-8278. doi: 10.1039/c9dt01235d. Epub 2019 May 17.

Authors

Qiang Chen¹, Hongyi Suo¹, Wenjuan Zhang², Randi Zhang¹, Gregory A Solan³, Tongling Liang¹, Wen-Hua Sun⁴

Affiliations

¹ Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China. whsun@iccas.ac.cn.
² Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China. whsun@iccas.ac.cn and School of Materials Science and Engineering, Beijing Institute of Fashion Technology, Beijing 100029, China. zhangwj@bift.edu.cn.
³ Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China. whsun@iccas.ac.cn and Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, UK. gas8@le.ac.uk.
⁴ Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China. whsun@iccas.ac.cn and State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China.

PMID: 31099370
DOI: 10.1039/c9dt01235d

Abstract

Six examples of dinuclear bis(imino)pyridine-cobalt(ii) complexes, [1,5-{2-(CMe[double bond, length as m-dash]N)-6-(CMe[double bond, length as m-dash]N(2,6-R¹₂-4-R²-C₆H₂))C₅H₃N}₂(C₁₀H₆)]Co₂Cl₄ (R¹ = Me, R² = H Co1; R¹ = Et, R² = H Co2; R¹ = ⁱPr, R² = H Co3; R¹ = Me, R² = Me Co4; R¹ = Et, R² = Me Co5; R¹ = CHPh₂, R² = Me Co6), have been prepared from the corresponding bis(tridentate) compartmental ligands (L1-L6) in reasonable yields. The molecular structures of Co3 and Co5 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 × 10⁷ gPE per·mol(Co) per·h for Co1/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[double bond, length as m-dash]CH₂) found to rise with the reaction temperature. By modulating the steric hindrance exerted by the ortho-R¹ substituents in the precatalyst, polyethylenes displaying a remarkably broad range of molecular weights could be obtained [from 4.52 kg mol^-1 (R¹ = Me) to 246.7 kg mol^-1 (R¹ = CHPh₂)].