Nickel ylide catalysts

Binuclear nickel ylide catalysts to get high density polyethylene in aqueous emulsion or miniemulsion 137... 

It was noted that norbomene-ethylene copolymers, obtained in the presence of the nickel ylide catalysts, can contain comonomer units in nearly equimolar proportions. The mechanism of the formation of these copolymers can be viewed as follows. The norbornene molecule coordinated with the Ni atom cannot insert itself into the Ni-phenyl or Ni-norbomyl bond for steric reasons, while the insertion of ethylene into these bonds takes place readily. This leads to copolymers in which comonomer units alternate with a high degree of regularity. 

Nickel Polymerization Catalysts with Ylide Steering Ligands... 

The entire process is schematized on Figure 4. In the first step, ethylene is oligomerized in the presence of a homogeneous nickel phosphine catalyst. This catalyst is a nickel hydride generated by reduction of a nickel salt in the presence of a chelating ligand such as diphenylphosphinobenzoic acid or by reaction of nickel(O) with a phosphorus ylide. 

Thus, we demonstrate that norbomene-ethylene copolymers can be synthesized using comparatively simple nickel phosphorylide complexes. Although these copolymerization catalysts are less active than the systems based on zirconocene and methylalumoxane, they do not require any cocatalyst (e.g. alumoxane, which is an expensive chemical). Moreover, the lower oxophility of nickel in the ylide catalysts allows ethylene to be copolymerized with functionalized norbomenes. 

Sulfonated nickel ylide complex is a potent single-component catalyst for ethylene oligomerization in aromatic and polar solvents [226]. The modification of this complex with various organoaluminum compounds (AlEtjCl/AlEtCU or AlEt-O-Et) results in the formation of a new catalytic system with 10-20 times higher activity in ethylene oligomerization in aromatic solvents compared with that of the original ylide [201,227-229]. 

Ethylene could also be oligomerized to normal a-olefins in aqueous CHjOH containing 0.5-20% water in the presence of nickel ylide [214]. The water improved the separation of the catalyst phase from the olefin-rich product phase, increased the purity of the a-olefin product, shifted the product distribution toward higher a-olefins and not affect the catalytic activity. 

Ylide Nickel Complexes Novel Polymerization Catalysts... 

We found that the reaction of bis(cyclooctadiene)nickel(0) with the two ylides ben-zoyhnethylene-triphenylphosphorane and methylene-trimethylphosphorane in toluene yields a highly active homogeneous catalyst (la) without any co-catalyst -the ethylene turnover being approximately tenfold compared to 2 [10]. 

Fig. 1.2 X-ray structure and charge distribution of the bis(ylide)nickel catalyst [NiPh(Ph2PCHCMeO)(i-PrjPCH2)].

The selectivity of the bis(ylide)nickel catalysts frequently favors the formation of linear macromolecules with unsaturated end groups. In this case the FTIR spectrum of a PE film of defined thickness shows almost exclusively methyl and vinyl end groups. Their presence in equal quantities proves linearity. An example for the catalytically controlled formation of linear, unbranched macromolecules is given in Eq. (12). 

Homogeneous ylide-nickel systems were combined with heterogeneous surface chromium(II) catalysts. Both separate catalyst systems work in the absence of aluminum alkyl co-catalysts. In this process the nickel complex is supported on the chromium contact, resulting in a new heterogeneous catalyst, which is active in the ediylene polymerization and where two different catalytic centers co-operate [14a, b]. 

The high polar group tolerance of co-catalyst-free ylide nickel catalysts makes them interesting candidates for fhe polymerization of polar monomers. In fact, quite a number of polar vinyl monomers can be homo- and copolymerized quite effectively. The mechanisms of initiation and chain propagation have not been elucidated yet. Especially, acrylic monomers are well suited. It is fhus possible to produce, for example, poly(methyl methacrylate), poly(efhyl acrylate) and poly-(butyl acrylate) in high yield [Eq. (15)]. 

Bis(ylide)nickel catalysts are of high chemical variability and show superior performance in the activation of unsaturated substrates such as acetylene. The normalized polymerization activity in dimethyl sulfoxide (DMSO) of 500 mol polymerized acetylene per mol nickel (h aim) by far exceeds that of structurally related phosphane catalysts by a similar order of magnitude as observed in ethylene polymerizations (see Sections 1.2 and 1.3.1). To our knowledge this activity even exceeds that of all other nickel catalysts reported so far (Fig. 1.4). 

The high polar group tolerance of ylide nickel catalysts enables the polymerization of acetylene in polymer solutions not only of low polarity but also of medium and high polarity. These options provide synthetic access to a wide range of novel matrix polyacetylenes (MATPAC). Examples of polymers that may be used as matrix... 

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