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Issue 13, 2011
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New tetradentate N,N,N,N-chelating α-diimine ligands and their corresponding zinc and nickel complexes: synthesis, characterisation and testing as olefin polymerisation catalysts

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Abstract

A series of zinc complexes of the general formula {[ZnCl(ArN[double bond, length as m-dash]C(An)–C(An)[double bond, length as m-dash]NAr)]+}2[Zn2Cl6]2− (where Ar = 2-(1-benzyl-1H-1,2,3-triazol-4-yl)phenyl 2a, 2-(1-(1-phenylethyl)-1H-1,2,3-triazol-4-yl)phenyl 2b, 2-(1-phenyl-1H-1,2,3-triazol-4-yl)phenyl 2c; An = acenaphthene backbone) were prepared by the condensation of acenaphthenequinone with the corresponding o-triazolyl-substituted anilines (2-(1-benzyl-1H-1,2,3-triazol-4-yl)aniline 1a, 2-(1-(1-phenylethyl)-1H-1,2,3-triazol-4-yl)aniline 1b, 2-(1-phenyl-1H-1,2,3-triazol-4-yl)aniline 1c) which were formed by the copper(I)-catalyzed Huisgen[3+2] dipolar cycloaddition between 2-ethynylaniline and the corresponding azides in high yields, using anhydrous ZnCl2 as the metal template, in boiling glacial acetic acid. Zinc complexes of the type [ZnCl(ArN[double bond, length as m-dash]C(An)–C(An)[double bond, length as m-dash]NAr)]+[ZnCl3(NCCH3)] (4a–c) were synthesized by crystallisation of the corresponding complexes 2a–c in acetonitrile, at −20 °C. After removal of zinc dichloride from complexes 2a–c by the addition of potassium oxalate, in dichloromethane, the tetradentate N,N,N,N-chelating α-diimine ligands of the type ArN[double bond, length as m-dash]C(An)–C(An)[double bond, length as m-dash]NAr (5a–c) were obtained. The new ligand precursors and zinc complexes were characterised by elemental analysis, 1H and 13C{1H} NMR spectroscopy, two-dimensional NMR spectroscopy, and X-ray diffraction. Reaction of the ligand precursors 5a–c with [NiBr2(DME)], in dichloromethane, gave nickel complexes of the type [NiBr2(ArN[double bond, length as m-dash]C(An)–C(An)[double bond, length as m-dash]NAr)] (6a–c). The results of single crystal X-ray diffraction characterisation and magnetic susceptibility measurements demonstrated that nickel complexes 6a–c possess octahedral geometries around the nickel atoms with variable configurations, the Br atoms of which can be ionized when dissolved in methanol. In preliminary catalytic tests, complexes 6a–c revealed to be active as catalysts for the polymerisation of norbornene and styrene, when activated by cocatalyst MAO. The characterisation of the polymers by 1H and 13C{1H} NMR spectroscopy, gel permeation chromatography/size-exclusion chromatography (GPC/SEC) revealed that these polymers were formed by a coordination addition mechanism.

Graphical abstract: New tetradentate N,N,N,N-chelating α-diimine ligands and their corresponding zinc and nickel complexes: synthesis, characterisation and testing as olefin polymerisation catalysts

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Publication details

The article was received on 29 Sep 2010, accepted on 21 Jan 2011 and first published on 23 Feb 2011


Article type: Paper
DOI: 10.1039/C0DT01308K
Citation: Dalton Trans., 2011,40, 3365-3380
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    New tetradentate N,N,N,N-chelating α-diimine ligands and their corresponding zinc and nickel complexes: synthesis, characterisation and testing as olefin polymerisation catalysts

    L. Li, C. S. B. Gomes, P. T. Gomes, M. T. Duarte and Z. Fan, Dalton Trans., 2011, 40, 3365
    DOI: 10.1039/C0DT01308K

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