gem-Dimethyl-substituted bis(imino)dihydroquinolines as thermally stable supports for highly active cobalt catalysts that produce linear PE waxes

Randi Zhang; Yongfeng Huang; Gregory A Solan; Wenjuan Zhang; Xinquan Hu; Xiang Hao; Wen-Hua Sun

doi:10.1039/c9dt01345h

gem-Dimethyl-substituted bis(imino)dihydroquinolines as thermally stable supports for highly active cobalt catalysts that produce linear PE waxes

Dalton Trans. 2019 Jun 21;48(23):8175-8185. doi: 10.1039/c9dt01345h. Epub 2019 May 15.

Authors

Randi Zhang¹, Yongfeng Huang², Gregory A Solan³, Wenjuan Zhang⁴, Xinquan Hu⁵, Xiang Hao⁶, Wen-Hua Sun¹

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 and CAS Research/Education Center for Excellence in Molecular Sciences and International School, University of Chinese Academy of Sciences, Beijing 100049, China.
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 College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China.
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@leicester.ac.uk.
⁴ Beijing Key Laboratory of Clothing Materials R&D and Assessment, Beijing Engineering Research Center of Textile Nanofiber, School of Materials Science and Engineering, Beijing Institute of Fashion Technology, Beijing 100029, China.
⁵ College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China.
⁶ 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.

PMID: 31089598
DOI: 10.1039/c9dt01345h

Abstract

Six types of 2,8-bis(imino)-7,7-dimethyl-5,6-dihydroquinoline, 2-(ArN[double bond, length as m-dash]CMe)-8-(ArN)-7,7-Me₂C₉H₆N (Ar = 2,6-Me₂C₆H₃L1, 2,6-Et₂C₆H₃L2, 2,6-ⁱPr₂C₆H₃L3, 2,4,6-Me₃C₆H₂L4, 2,6-Et₂-4-MeC₆H₂L5, 2,4,6-^tBu₃C₆H₃L6), distinguishable by their steric and electronic profile, are described that can readily undergo complexation with cobaltous chloride to form their corresponding LCoCl₂ chelates, Co1-Co6. The molecular structures of Co2 and Co3 reveal square pyramidal geometries with ring puckering a feature of the gem-dimethyl section of their unsymmetrical N,N,N'-ligands. On activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all the cobalt complexes exhibited exceptionally high activities for ethylene polymerization with levels reaching up to 1.19 × 10⁷ g PE per mol (Co) per h for mesityl-containing Co4. Significantly, these catalysts exhibited good thermal stability by displaying their optimal performance at temperatures up to 70 °C whilst also maintaining appreciable catalytic lifetimes. With the exception of that obtained using the most sterically hindered Co6 (2,4,6-t-butyl), the polyethylenes are of low molecular weight (M_w≤16.0 kg mol^-1) and of narrow dispersity (M_w/M_n≤3.4). Moreover, end-group analysis of these highly linear polymer waxes reveals evidence for unsaturated as well as various levels of fully saturated materials highlighting the role of both β-H elimination and chain transfer to aluminum as termination pathways.