Novel nickel(II) and copper(II) complexes with phenoxy-imidazole ligands: Syntheses, crystal structures and norbornene addition polymerization

The novel nickel(II) (1) and copper(II) (2) complexes bearing 2′-(4′,6′-di-tert-butylhydroxy-phenyl)-1,4,5-triphenyl imidazole ligand have been synthesized and characterized. The molecular structure analyses of complexes 1 and 2 indicated that Ni(II) centre in 1 adopts a distorted tetrahedral coordination geometry with a dihedral angle of 85.2° between Ni(1)O(1)N(1) plane and Ni(1)O(1A)N(1A) plane, while the Cu(II) centre in 2 represents a distorted square planar coordination geometry with a cis-N2O2 arrangement of the donor atoms, the dihedral angle being 32° between Cu(1)O(1)N(1) plane and Cu(1)O(1A)N(1A) plane. After activation with methylaluminoxane (MAO), both Ni(II) and Cu(II) complexes can be used as catalysts for the addition polymerization of norbornene (NB). The polynorbornenes (PNBs) are produced with very high polymerization activity (108 g PNB mol−1 Ni h−1) for Ni(II) complex and moderate catalytic activity (105 g PNB mol−1 Cu h−1) for Cu(II) complex, respectively. The high molecular weight polynorbornenes (106) are obtained for complexes 1 and 2. Moreover, the distinct effects of polymerization temperature and Al/M ratio on catalytic activities and molecular weights of polymers are discussed.

Graphical abstractNickel and copper complexes 1 and 2 with phenoxy-imidazole ligands have been synthesized, characterized and used as catalysts for the addition polymerization of norbornene in the presence of methylaluminoxane (MAO) as co-catalyst in high activities.Figure optionsDownload full-size imageDownload as PowerPoint slide