Bis-(salicylaldehyde-benzhydrylimino)nickel complexes with different electron groups: crystal structure and their catalytic properties toward (co)polymerization of norbornene and 1-hexene

摘要

Eight bis-(salicylaldehyde-benzhydrylimino)nickel complexes with different electron groups (Ni1–Ni8), Ni{(3-R _(1) )(5-R _(2) )C _(6) H _(2) (O)CHNCH(C _(6) H _(5) ) _(2) } _(2) , (R _(1) = H, R _(2) = H, Ni1; R _(1) = H, R _(2) = CH _(3) , Ni2; R _(1) = H, R _(2) = OCH _(3) , Ni3; R _(1) = H, R _(2) = Br, Ni4; R _(1) = CH _(3) , R _(2) = H, Ni5; R _(1) = OCH _(3) , R _(2) = H, Ni6; R _(1) = Br, R _(2) = Br, Ni7; R _(1) = Cl, R _(2) = Cl, Ni8), were synthesized and their crystal structures were characterized using single crystal X-ray diffraction. The results revealed that Ni1–Ni6 belong to the monoclinic system (space group P 2(1)/ n ), Ni7 belongs to the monoclinic system (space group C 2/ c ) and Ni8 belongs to the triclinic system (space group P ). All nickel complexes exhibited high activities (0.46–2.07 × 10 ~(6) g _(polymer) mol _(Ni) ~(?1) h ~(?1) ) toward norbornene homopolymerization, and a strong electron-withdrawing group on the salicylaldimino aromatic ring can enhance the catalytic activity and favor polymerization. Ni1 and Ni2 exhibited high activities (0.55–2.40 × 10 ~(5) g _(polymer) mol _(Ni) ~(?1) h ~(?1) ) toward copolymerization of norbornene and 1-hexene in the presence of B(C _(6) F _(5) ) _(3) . The 1-hexene content in the copolymers could be controlled up to 7.98–12.50% by varying the comonomer feed ratio of 1-hexene from 10 to 50%. It is observed that when the 5-position of the salicylaldimino aromatic ring has a substituent (–CH _(3) ), the 1-hexene insertion rate is lower than that without a substituent. In addition, the polymers showed high molecular weights (1.5–2.4 × 10 ~(5) g mol ~(?1) ) and narrow molecular weight distributions (1.62–1.89). The obtained polymers were also verified to be amorphous copolymers and had high thermal stability, good solubility and optical transparency.