Synthesis of bis-(benzocyclohexan-ketoimino) Ni(ii) with different electron groups and their catalytic copolymerization of norbornene and polar norbornene?

RSC Advances Pub Date: 2017-10-17 DOI: 10.1039/C7RA09944D

Abstract

Four N,O-chelating type bidentate ligand nickel(II) complexes, Ni{C10H8(O)C[ArN]CH3}2, two of them containing electron-donating groups (Ni1: Ar = p-PhCH3, Ni2: Ar = p-PhOCH3) and another two containing electron-withdrawing groups (Ni3: Ar = p-PhF, Ni4: Ar = p-PhCF3), were synthesized and the molecular structures of Ni2, Ni3 and Ni4 were determined by X-ray crystallography. Copolymerization of norbornene (NB) and 5-norbornene-2-carboxylic acid methyl ester (NB-COOCH3) were carried out in toluene with the above complexes as catalyst precursors and B(C6F5)3 as the co-catalyst. All complexes showed high catalytic activity toward the copolymerization (up to 2.80 × 105 gpolymer molNi?1 h?1) and the complexes with electron-withdrawing groups (Ni3 and Ni4) showed higher catalytic activity, and the activity was enhanced with the increased electron-withdrawing ability of the substituent (Ni4 > Ni3). The obtained poly(NB-co-NB-COOCH3)s were confirmed to be vinyl-addition copolymers and non-crystalline. All copolymers exhibited better solubility in common organic solvents, and showed high molecular weights (up to the grade of 105 g mol?1) and good thermal stability (Td > 370 °C). Meanwhile, variation of the substituted electron group could slightly affect the above-mentioned copolymers' properties.

Graphical abstract: Synthesis of bis-(benzocyclohexan-ketoimino) Ni(ii) with different electron groups and their catalytic copolymerization of norbornene and polar norbornene
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