The second coordination sphere effect of benzothiophene groups enhances chain transfer in ethylene (co)oligomerization

Recently, the second coordination sphere effect has been successfully exploited to modulate the catalytic behavior of late-transition metal catalysts in olefin insertion polymerization. In this study, four bulky iminopyridyl Ni( ii ) and Pd( ii ) complexes that contain naphthalene or benzothiophene groups were firstly prepared and their applications in olefin oligomerization were also investigated. The as-prepared nickel and palladium complexes generally displayed good catalytic activity in ethylene oligomerization, providing hyperbranched oligomers with various microstructures. Notably, the molecular weights of the ethylene oligomers generated by the benzothiophene-based Ni( ii )/Pd( ii ) complexes were significantly lower than those generated by the naphthalene-based complexes. In addition, these palladium complexes could catalyze the co-oligomerization of ethylene and MA, yielding hyperbranched co-oligomers with tunable incorporation ratios of MA. Moreover, for ethylene oligomerization catalyzed by nickel complexes, toluene-end-functionalized branched ethylene oligomers were formed via Friedel-Crafts addition of the resulting unsaturated ethylene oligomers to the toluene solvent. In this work, we found that the second coordination sphere effect of benzothiophene could facilitate chain transfer in iminopyridyl Ni( ii )/Pd( ii )-catalyzed ethylene (co)oligomerization, in contrast to the phenomenon observed in the corresponding α-diimine system. The second coordination sphere effect of benzothiophene groups could facilitate the chain transfer in iminopyridyl Ni( ii )/Pd( ii )-catalyzed ethylene (co)oligomerization, in contrast to the phenomenon observed in the corresponding α-diimine system.