Nickel complexes bearing different electron groups on substituted salicylaldnaphthylmethyleneimine ligands: Syntheses and their catalytic performance for (co)polymerization of norbornene

Abstract

Novel nickel complexes bearing different electron groups on substituted salicylaldnaphthylmethyleneimine ligands, bis‐(salicylaldnaphthylmethyleneimino)Ni(II) (Ni{(3‐R1)(5‐R2)C6H2(O)CH[N (naphthyl‐CH2)]}2 Ni1: R1 = H, R2 = H; Ni2: R1 = H, R2 = CH3; Ni3: R1 = H, R2 = Br; Ni4: R1 = H, R2 = OCH3; Ni5: R1 = CH3, R2 = H; Ni6: R1 = Br, R2 = H), were synthesized. Ni2, Ni3, Ni5, and Ni6 are clearly characterized by single‐crystal X‐ray diffraction. Co‐polymerization of norbornene (NB) with 5‐norbornene‐2‐methylene butyl ether (BN) was carried out in toluene with the aforesaid complexes as catalyst precursors and B(C6F5)3 as the co‐catalyst. Catalyst activity, molecular weight, thermal stability, solubility, regularity, and optical transparency were investigated, and the mechanism of the electron groups changing catalyst performance is explained. All catalysts show high activity toward co‐polymerization (up to 3.53 × 105 gpolymer molNi−1 h−1). Ni3 shows the highest activity and Ni5 shows the highest insertion rate (up to 37.6%). The obtained poly(NB‐co‐BN)s are confirmed to be vinyl‐addition‐type co‐polymers, and they are noncrystalline. The co‐polymers exhibited excellent thermal stability and processability (Td ≥ 400 °C, Tg < 240 °C), optical transparency (up to 90%), and good solubility.