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Eight bis-(salicylaldehyde-benzhydrylimino)nickel complexes with different electron groups (Ni1–Ni8), Ni{(3-R1)(5-R2)C6H2(O)CHNCH(C6H5)2}2, (R1 = H, R2 = H, Ni1; R1 = H, R2 = CH3, Ni2; R1 = H, R2 = OCH3, Ni3; R1 = H, R2 = Br, Ni4; R1 = CH3, R2 = H, Ni5; R1 = OCH3, R2 = H, Ni6; R1 = Br, R2 = Br, Ni7; R1 = Cl, R2 = 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 P2(1)/n), Ni7 belongs to the monoclinic system (space group C2/c) and Ni8 belongs to the triclinic system (space group P). All nickel complexes exhibited high activities (0.46–2.07 × 106 gpolymer molNi−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 × 105 gpolymer molNi−1 h−1) toward copolymerization of norbornene and 1-hexene in the presence of B(C6F5)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 (–CH3), the 1-hexene insertion rate is lower than that without a substituent. In addition, the polymers showed high molecular weights (1.5–2.4 × 105 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.

rsc advances

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