Nickel complexes polymer-supported catalysts

Nickel and palladium react with a number of olefins other than ethylene, to afford a wide range of binary complexes. With styrene (11), Ni atoms react at 77 K to form tris(styrene)Ni(0), a red-brown solid that decomposes at - 20 °C. The ability of nickel atoms to coordinate three olefins with a bulky phenyl substituent illustrates that the steric and electronic effects 54,141) responsible for the stability of a tris (planar) coordination are not sufficiently great to preclude formation of a tris complex rather than a bis (olefin) species as the highest-stoichiometry complex. In contrast to the nickel-atom reaction, chromium atoms react (11) with styrene, to form both polystyrene and an intractable material in which chromium is bonded to polystyrene. It would be interesting to ascertain whether such a polymeric material might have any catal3d ic activity, in view of the current interest in polymer-supported catalysts (51). 

Optically active l,l -binaphthols are among the most important chiral ligands of a variety of metal species. Binaphthol-aluminum complexes have been used as chiral Lewis acid catalysts. The l,T-binaphthyl-based chiral ligands owe their success in a variety of asymmetric reactions to the chiral cavity they create around the metal center [107,108]. In contrast with the wide use of these binaphthyls, the polymer-supported variety has been less popular. The optically active and sterically regular poly(l,l -bi-naphthyls) 96 have been prepared by nickel-catalyzed dehalogenating polycondensation of dibromide monomer 95 (Sch. 7) [109] and used to prepare the polybinaphthyl aluminum(III) catalyst 97 this had much greater catalytic activity than the corresponding monomeric catalyst when used in the Mukaiyama aldol reaction (Eq. 29). Unfortunately no enantioselectivity was observed in the aldol reaction. 

Different conditions (including additives and solvent) for the reaction have been reported,often focusing on the palladium catalyst itself," or the ligand." Catalysts have been developed for deactivated aryl chlorides," and nickel catalysts have been used." Modifications to the basic procedure include tethering the aryl triflate or the boronic acid to a polymer, allowing a polymer-supported Suzuki reaction. Polymer-bound palladium complexes have also been used." " The reaction has been done neat on alumina," and on alumina with microwave irradiation." Suzuki coupling has also been done in ionic liquids," in supercritical... 

The reaction of halogenated polystyrene with tetrakisftriphenylphos-phine) nickel gives a supported complex. This system, when associated with boron trifluoride etherate, is a catalyst for the dimerization of ethylene. Indeed, at 0°C and atmospheric pressure of ethylene, a suspension in toluene of the polymer-nickel complex, to which has been added BFj-EtjO (BFj/Ni = 20/1 mole), absorbs ethylene selectively, giving butene 1231). 

The direct addition of BF3 and water onto the solid nickel-polymer complex gives a catalyst that exhibits an induction period before the dimerization of ethylene is effective. However, the preformation of the catalyst in a solvent like hexane gives a catalyst that shows no induction period. This can be understood in terms of a physical effect on the support. Indeed, in the latter case the solvent remaining in the polymer leaves it swelled, thus allowing the immediate access of ethylene to the catalytic sites. In the former case, in contrast, the formation of some dimer is required to play the role of a solvent and to promote the progressive swelling of the support. 

There are reports [592-594] on the dimerization of propylene catalyzed by heterogenized (ir-allyDnickel halides. Polymer-anchored -ir-allylic nickel complexes similar to nonsupported complexes are found to be effective catalysts for propylene dimerization after activation with a Lewis acid such as EtAlCL (molar ratio of Al/Ni = 15 5). Using a crosslinked resin as a support, the dimerization can be performed continuously, since the catalytic centers remain active for a long time without any further addition of aluminum cocatalyst. The release of metals during this reaction is low. The reactions are carried out either in bulk propylene or in chlorobenzene solution. The conversion reaches 95% at room temperature. The product has the composition of 2% dimethylbutenes, 67% methylpentenes, and 31% hexenes. Hexene content obtained with polymer-anchored nickel catalyst... 

Polystyrene supported nickel(II) carborane complexes 44a and 44b have been tested in the polymerisation of ethylene, styrene and vinyl chloride in [C4Ciim][BF4], The compounds were active for all three substrates, even in the absence of a co-catalyst. Increased catalytic activity was observed relative to THF, affording polymers with higher molecular weight and, in most cases, lower polydispcrsity.1671... 

Cyclopentadiene itself has been used as a feedstock for carbon fiber manufacture (75). It is also a component of supported metallocene-alumoxane polymerization catalysts in the synthesis of polyethylene and polypropylene polymers (76), as a nickel or iron complex in the production of methanol and ethanol from synthesis gas (77), and as Group VIII metal complexes for the production of acetaldehyde from methanol and synthesis gas (78). 

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