N,O-chelating bidentate Ni (II) and Pd (II) complexes for copolymerization of norbornene and norbornene ester

Abstract

A series of N,O-chelating type bidentate ligands nickel (II) and palladium (II) complexes Mt[C10H8(O)C(ArN)CH3]2 [Ar = 2,6-C6H3(CH3)2, Mt = Ni (II) (C1) and Mt = Pd (II) (C2); Mt = Ni (II), Ar = 2,6-C6H3Cl2 (C3) and Ar = 2,6-C6H4Cl (C4)] were synthesized and characterized by single crystal X-ray diffractions. Homo-polymerization and copolymerization of norbornene (NB) and 5-norbornene-2-carboxylic acid methyl ester (NB-COOCH3) proceeded in toluene with the above complexes as catalyst precursors and tris(pentafluorophenyl)borane [B(C6F5)3] as a unique co-catalyst. Higher activity was observed for complexes with electron-donating ortho-substituents on arylimino, which resulted in activity order C1 > C3, and higher activity was observed for bulky ortho-substituents on arylimino, which resulted in activity order C3 > C4. The C2 system presented much lower catalytic activity toward copolymerization of NB and NB-COOCH3, while the C1 and C3 system showed high catalytic activity and produced the copolymers with relatively high molecular weights, as well as narrow distribution. The fraction of NB-COOCH3 in copolymer can reach up to 44.6 mol% in the presence of C1 by controlling monomer feed ratio of 50%. The achieved vinyl-addition type copolymers displayed high transparency, good thermal stability and solubility in common solvents. The reactivity ratios of co-monomers were rNB-COOCH3 = 0.5 and rNB = 0.72 under the catalytic system of C1.