om3004509_si_012.cif (62.58 kB)

(“Ferrocene-salaldiminato”)zirconium Complexes for Ethylene Polymerization Catalysis: The Role of the Bulky Substituents

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posted on 08.10.2012 by Xiaowu Wang, Roland Fröhlich, Constantin G. Daniliuc, Bernhard Rieger, Aleksandra Jonovic, Gerald Kehr, Gerhard Erker
We prepared the 2-hydroxy-5-trimethylsilylferrocenecarbaldimine systems 13 enantioselectively by a short synthetic route starting from the chiral ferrocene carbaldehyde acetal 5. The imines 13a–c were used to synthesize the zwitterionic (“ferrocene-salaldiminato”)2ZrCl4 complexes 14ac. Activation with MAO gave homogeneous Ziegler–Natta catalysts, which showed only a moderate ethylene polymerization activity, similar to the unsubstituted parent “ferrocene-salaldiminato” zirconium systems. Consequently, a synthetic route was devised and carried out to make the corresponding 2-hydroxy-3,5-bis­(trimethylsilyl)­ferrocenecarbaldimines (21) available. The enantiomerically highly enriched ligands (pS)-21a and -d derived from the aldehyde and aniline or cyclohexylamine, respectively, were used to synthesize the corresponding (“ferrocene-salaldiminato”)2ZrCl4 complexes 22a,d. Both gave highly active homogeneous Ziegler–Natta catalysts upon activation with MAO for the formation of linear low molecular weight polyethylene. Complex 22d and many ligand precusors from both sequences were characterized by X-ray diffraction.

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