We recently reported on highly active Ni-catalyst systems for ethene polymerization. These were generated from bis(cyclooctadiene)nickel(o), Ni(cod),, a carbonylstabilized and a non-stabilized ylide, Ph3PCRiC(0)R2 and R2PCR4RS, respectively.[" In the catalytically active, square-planar nickel complex, the non-stabilized ylide is structuraAy intact C-coordinated, whereas the stabilized ylide is PO-coordinated due to rearrangement. The activity of the catalyst can be optimized by variation of the intact ylide ligand; but modification of the substituent R2 in the carbonyl-stabilized ylide ligand also increases the catalytic activity in the Ni(cod),/Ph3PCHC(O)R2/Me,PCH, system : On going from the formylmethylene(tripheny1)phosphorane l a via the acetyl derivative l b to the benzoylmethylene(tripheny1)phosphorane l c (R2 = H, Me, Ph) the turnover number increases to ca. 0.5 x lo5 moles ethene per mole of nickel.['I Characterization of the polymers showed that the average chain length of the ethene polymerizates also increases with increasing catalyst activity. The intrinsic viscosities in tetralin at 140°C do not, however, exceed 0.2 dL/g, which corresponds to molecular weights M of about 5 x lo3 g/ mole.[*I We have therefore tried to noticeably increase the range of molecular weights accessible with this Ni-catalyst system by further variation of the carbonyl-stabilized ylide ligand.With the three ligands 2a-2c, we have indeed been able to obtain novel, very active bis(y1ide)nickel polymerization catalysts, which afford access to polyethene (PE) in practically all molecular weight ranges from PE waxes and hard waxes through high molecular weight high-density polyethene (HDPE) to ultrahigh molecular weight polyethene (UHMW-PE) with M > lo6 g/mole (Table I). 2a 2 b 2c
The nickel complex 1 contains a structurally intact and a carbonyl‐stabilized rearranged ylide ligand. Such bis(ylide) complexes are highly active in the polymerization of ethylene; activities of 0.5 × 105 moles of ethylene per mole of 1 are not uncommon.
Suitable as highly effective polymerization catalysts is the new class of donor/acceptor metallocenes in which the rotation of the two pi ligands is restricted through the formation of a dative D(+)-->A(-) bond (see picture). Specifically optimized substitution patterns yield excellent properties for the synthesis of high-melting, highly crystalline thermoplastic materials, amorphous thermoplastic materials with high glass transition temperatures as well as polyolefin elastomers with low glass T(g).
Superkunststoff! Donor‐Acceptor‐Zirconocene mit einem Donor(P)‐substituierten Fluorenylliganden und einem Acceptor(B)‐substituierten Cyclopentadienylliganden (siehe Struktur) katalysieren die Ethylenpolymerisation mit hoher Aktivität und enormer Selektivität für das Kettenwachstum selbst bei hohen Temperaturen und machen so ultrahochmolekulare Polyethylene zugänglich (viskositätsgemittelte Molekulargewichte Mη>1×106 g mol−1).
Polyethen in praktisch allen Molekulargewichtsbereichen–von Polyethen‐Wachsen und Hartwachsen über „high density”︁‐Polyethen bis hin zum ultra‐hochmolekularen Polyethen – ist mit neuen, sehr aktiven Bis(ylid)nickel‐Katalysatoren zugänglich. Die Katalysatoren werden aus Bis(cyclooctadien)nikkel(0), den carbonylstabilisierten Ylid‐Liganden 1–3 und einem nichtstabilisierten Ylid hergestellt.
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