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  • Author: Bernhard Rieger x
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Neuorientierung und Tradition in der Bundesrepublik der 1950er und 60er Jahre

The synthesis of a series of C1-symmetric metallocene complexes rac-[1-(5,6-dialkoxy-2-methyl- 1-η5-indenyl)-2-(9-η5-fluorenyl)ethane]zirconium dichlorides (alkyl: n-butyl, n-hexyl, n-octyl, n-decyl) is described. These complexes are versatile catalysts in the polymerization of propylene after in situ activation with triisobutylaluminum (TIBA) and Ph3C[B(C6F5)4] in toluene and heptane solution. All catalysts show higher solubility and improved polymerization properties in industrially used hydrocarbon solvents (e.g. heptane). However, the molecular weights and isotacticity values of the resulting polypropylene materials are decreased compared to the ethoxy-bridged analogue rac- [1-(5,6-ethylenedioxy-2-methyl-η5-indenyl)-2-(9-η5-fluorenyl)ethane]zirconium dichloride. A possible explanation is based on enhanced interaction of the active catalyst centers with Al(III) scavenger molecules even at low Al : Zr ratios, leading to reversible chain transfer.

Anhydrous MgCl2 was reacted with 2 equiv. of ethanol to generate the MgCl2(EtOH)2 adduct 1. An appropriate amount of higher alcohol having a long carbon chain, such as 1-decanol, was anchored on the surface of a part of adduct 1 to give a mixture of MgCl2 adducts having an internal surfactant. A multifunctional polymer/oligomer, e. g. poly(ethylene glycol)-200 (PEG-200), was introduced into this system yielding a composite of liquid inorganics and polymers (CLIP). Under the regulation of the internal surfactant and the multifunctional polymer, this composite was melted and dispersed in an inert hydrocarbon solvent under vigorous agitation at elevated temperatures followed by fast cooling to generate a MgCl2-based spherical catalyst support precursor. SEM pictures show that this support precursor has a narrow particle size distribution, and its surface structure is an intricate combination of smaller MgCl2-based crystallites.

A modification of the previously developed synthetic approach towards dinuclear flexibly linked salphen complexes is successfully utilized for the preparation of heterodinuclear salphen dimers. A dinuclear salphen species with Pd(II) and Cr(III) centers bears a stronger structural resemblance to the related bis-Cr(III) compound than the corresponding mononuclear Cr(III) salphen complex. Therefore, it was considered as a more useful model for the comparison with the homobinuclear Cr(III) complex regarding the catalytic activity in the ring-opening polymerization of β-butyrolactone, for which a bimetallic catalytic mechanism seems to operate. The polymerization results again have shown a higher activity of the homobinuclear Cr(III) complex.

Palladium complexes of two different P,N ligands (a phosphane-pyridine and a phosphane-imine ligand) were synthesized and characterized. Single crystal X-ray structure analyses of the palladium diiodide compounds revealed a square-planar coordination geometry at the metal center with a longer Pd-I bond in trans-position to the phosphorus atom. The chloro-methyl palladium species of the phosphane-pyridine ligand was applied for the oligomerization of ethene using a borate salt as cocatalyst.

Non-symmetric diimine ligands (Ar-N=C(CH3)-(CH3)C=NAr*; Ar: 2,6-diisopropyl-phenyl; Ar*: 2,6-di(4-tert-butyl-phenyl)phenyl (4b), 2,6-di(4-OCH3)-phenyl)phenyl (4c)) were synthesized and converted in-situ into the corresponding nickel dibromo complexes (5b, c) by reaction with (DME)NiBr2. The complexes were activated for ethene polymerization by treatment with MAOat ambient temperature. The resulting highmolecular weight polymer products (MW > 4.0 x 106 g mol-1) have a branched microstructure (predominantly methyl groups), as indicated by 13C NMR spectroscopy. The degree of branching can be controlled by a proper choice of the 2,6-diphenyl modified aniline moieties resulting in melting transitions ranging from 92 - 130 °C.