A rigid-flexible double-layer steric strategy for ethylene (co)oligomerization with pyridine-imine Ni(ii) and Pd(ii) complexes

Abstract

Late transition-metal-based catalysts have been extensively used in olefin oligomerizations for decades. In this study, a series of N-terphenyl pyridine-imine Ni(II) and Pd(II) complexes bearing rigid-flexible double-layer steric substituents were...

Synthesis of High-Molecular-Weight Branched Polyethylene Using a Hybrid “Sandwich” Pyridine-Imine Ni(II) Catalyst

“…As opposed to the fact that the pyridine-imine catalysts usually generate low-molecular-weight polyethylene or copolymers in ethylene (co)polymerization due to the unilateral axial steric structure of the pyridine-imine ligand, all these Ni(II) complexes in our case yielded polyethylene with high molecular weight (level of 100 kg/mol), one or two orders of magnitude higher than those obtained in most reported pyridine-imine systems ( Figure 5 ). ( Laine et al, 1999 ; Meneghetti et al, 1999 ; Laine et al, 2000 ; Bianchini et al, 2010 ; Sun et al, 2012 ; Yue et al, 2014 ; Sun et al, 2015a ; Sun et al, 2015b ; Huang et al, 2015 ; Chen et al, 2016 ; Huang et al, 2016 ; Guo et al, 2019 ; Wang et al, 2020b ; Fan et al, 2021 ; Li and Dai, 2021 ; Peng et al, 2021 ; Yan et al, 2022 ) This is mainly attributed to the synergistic effect of 8-arylnaphthyl and diarylmethyl groups, which form a sandwich-like structure that can effectively retard chain transfer during polymerization. In particular, Ni5 is capable of generating the highest molecular weight of polyethylene among these catalysts ( Figure 2B ).…”

“…( Peng et al, 2021 ; Li and Dai, 2021 ) In contrast, the pyridine-imine consisting of N-terphenyl structure failed to retard chain transfer, thus only hyperbranched ethylene oligomers and ethylene-methyl acrylate (MA) co-oligomers can be obtained ( Chart 1D ). ( Fan et al, 2021 ; Yan et al, 2022 ; Fan et al, 2022 ) In addition, the effectiveness of a single dibenzosuberyl group in unsymmetrical iminopyridyl Ni(II) and Pd(II) catalysts in retarding the chain transfer was also demonstrated ( Chart 1E ). ( Ge et al, 2021 ) In this study, the dibenzosuberyl and 8-aryl-naphthyl units are integrated into the pyridine-imine nickel catalyst at the same time and the resulting hybrid “sandwich” catalyst is capable of catalyzing ethylene polymerization to yield highly branched polyethylene with high molecular weights ( Chart 1F ).…”

Direct synthesis of hyperbranched ethene oligomers and ethene‐MA co‐oligomers using iminopyridyl systems with weak neighboring group interactions

“…[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] Recently, we developed a series of N-terphenyl iminopyridyl Ni(II) and Pd(II) complexes and they were highly effective in the preparation of hyperbranched ethene oligomers and ethene-MA co-oligomers (Chart 1D). [32][33] A π-interaction of a phenyl group with the metal center is responsible for the results of the above experiments. Mecking and Marks et al elaborated this weak neighboring group interactions in a neutral N,O-salicylaldiminato Ni(II) system (Chart 1E,F).…”

Ethylene (co) oligomerization using iminopyridyl Ni(II) and Pd(II) complexes bearing benzocycloalkyl moieties to access hyperbranched ethylene oligomers and ethylene-MA co-oligomers

“…Compared to the widely used α-diimine systems, which are typically used to prepare polyethylene or ethylene-based copolymers of high molecular weights, these iminopyridyl catalysts possessing a unilateral steric hindrance are known for the synthesis of low molecular weight polyethylene ( Chart 1A ). ( Laine et al, 1999 ; Meneghetti et al, 1999 ; Laine et al, 2000 ; Bianchini et al, 2010 ) Many improvements in terms of catalytic activity, thermal stability and properties of the resulting polymer have been made via the introduction of bulky ortho-aryl substituents, modification of the pyridine backbone and electronic tuning ( Chart 1 ) ( Yue et al, 2014 ; Huang et al, 2015 ; Chen et al, 2016 ; Dai et al, 2016 ; Huang et al, 2016 ; Chen et al, 2018 ; Guo et al, 2019b ; Dai and Li, 2020 ; Ge et al, 2021 ; Li and Dai, 2021 ; Peng et al, 2021 ; Fan et al, 2022a ; Fan et al, 2022b ; Yan et al, 2022a ). Among all the modified catalysts, a series of half “sandwich” iminopyridyl Ni(II) and Pd(II) complexes bearing an 8-aryl-naphthyl substituent ( Chart 1B ) and rotation-restricted iminopyridyl Ni(II) and Pd(II) complexes with dibenzosuberyl groups ( Chart 1C ) can effectively suppress chain transfer in ethylene polymerization to yield high-molecular-weight polyethylene and ethylene-based copolymers ( Chen et al, 2016 ; Dai et al, 2016 ; Dai and Li, 2020 ; Ge et al, 2021 ; Li and Dai, 2021 ; Peng et al, 2021 ).…”

“…Among all the modified catalysts, a series of half “sandwich” iminopyridyl Ni(II) and Pd(II) complexes bearing an 8-aryl-naphthyl substituent ( Chart 1B ) and rotation-restricted iminopyridyl Ni(II) and Pd(II) complexes with dibenzosuberyl groups ( Chart 1C ) can effectively suppress chain transfer in ethylene polymerization to yield high-molecular-weight polyethylene and ethylene-based copolymers ( Chen et al, 2016 ; Dai et al, 2016 ; Dai and Li, 2020 ; Ge et al, 2021 ; Li and Dai, 2021 ; Peng et al, 2021 ). In contrast, N-teraryl iminopyridyl Ni(II) and Pd(II) catalysts with weak neighboring group interactions were prone to simultaneous chain walking and chain transfer reactions, thus facilitating the synthesis of hyperbranched ethylene oligomers and ethylene-MA co-oligomers ( Charts 1E,G ) ( Fan et al, 2022a ; Fan et al, 2022b ; Yan et al, 2022a ). More interestingly, the hybridized form of the mentioned above two types ( Charts 1C,E ) was also highly effective in suppressing chain transfer in ethylene polymerization to yield high-molecular-weight polyethylene ( Chart 1F ) ( Ge et al, 2021 ).…”