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

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 P2(1)/n), Ni7 belongs to the monoclinic system (space group C2/c) and Ni8 belongs to the triclinic system (space group P1̄). 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.