| Abstract
| - The present contribution reports on a series of new diimine ligands and complexes bearing 2,6-diphenyl-modified aniline moieties. The influence of different substituents on the complex structures as well as on their polymerization behavior was investigated. Interestingly the racemic complex 4c adopts a chiral, C2-symmetric coordination geometry, due to a distinct repulsion of the tert-butyl fragments.
- Four new 1,4-diaza-2,3-dimethylbutadiene ligands (Ar−NC(CH3)−(H3C)CNAr; Ar: 3a= 2,6-diphenylphenyl; 3b = 2,6-di(4-OCH3-phenyl)phenyl; 3c = 2,6-di(4-tert-butyl-phenyl)phenyl; 3d = 2,6-di(3,5-dimethylphenyl)phenyl) as well as the palladium dichloride complexes4a−c and methyl monochloride derivatives 5a−c were prepared, and their polymerizationbehavior was investigated. The corresponding nickel species 6a−c were tested for theinsertion polymerization of ethene by in situ reactions of 3a−c with (DME)NiBr2. The ligandsare accessible by a three-step procedure. Aryl boronic acids were prepared by Grignardreactions of substituted aryl bromides and were coupled with 2,6-dibromo aniline accordingto a Suzuki cross-coupling protocol to give the corresponding terphenyl anilines 2a−d.Condensation of 2,3-butanedione with the corresponding aniline afforded the formation ofthe diimines 3a−d. The corresponding palladium dichloride complexes 4a−c are accessibleby reaction with (PhCN)2PdCl2. The structures of 4a−c could be determined by X-rayanalysis. While the terphenyl complex 4a adopts a C2v-symmetry, 4c exists in a chiral C2-symmetric coordination geometry, due to the repulsive interactions of the stericallydemanding tert-butylphenyl substituents of the aniline moieties. All palladium and nickelcomplexes are catalysts for the polymerization of ethene. However, the chiral Ni(II) complex6c shows by far the highest polymerization activity up to 2 × 104 kg(PE) [mol (Ni) h]-1. Thepolyethenes obtained with the palladium methyl monochloro catalysts activated with Na[(3,5-(CF3)2C6H3)4B] and the nickel dibromo complexes activated with MAO are linear andshow in the case of the Ni(II) derivatives molecular weights up to 4.5 × 106 g mol-1 (Mw/Mn≈ 2), which can be controlled by addition of hydrogen.
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