Nickel-butadiene dimer complex, catalyst

The patent literature contains several references to the use of sulfoxide complexes, usually generated in situ, as catalyst precursors in oligomerization and polymerization reactions. Thus, a system based upon bis(acrylonitrile)nickel(0> with added Me2SO or EtgSO is an effective cyclotrimerization catalyst for the conversion of butadiene to cyclo-1,5,-9-dodecatriene (44). A similar system based on titanium has also been reported (407). Nickel(II) sulfoxide complexes, again generated in situ, have been patented as catalyst precursors for the dimerization of pro-pene (151) and the higher olefins (152) in the presence of added alkyl aluminum compounds. 

Butadiene dimerization catalysts have been quite extensively studied, although the major effort has been concentrated on homogeneous catalyst systems using complexes containing nickel (167), iron (168), cobalt (169), and palladium (170). 

A chelating diphosphite prepared from biphenol and PCI3 provides a very stable Ni(0) complex that catalyzes the hydrocyanantion of butadiene without excess ligand. Although the stability of this catalyst is enhanced, the amount of butadiene dimerization byproducts is significant. A related nickel catalyst prepared using a chiral chelating diphosphite based on I -2,2 -binaphthol provides enantioselectivity in the hydrocyanation of norbomene. The major product, J -exo-2-cyanonorbomane, was obtained in an enantiomeric excess of up to 38%. 

Conditions have been described whereby butadiene is dimerized to a mixture of octadienes, using N-hydroxymorphoIine and nickel(O) phosphine complexes/ or to octadienyl ethers using palladium catalysts in alcohol. In both cases minimal formation of octatriene products is observed. 

The trans isomer of 1,4-hexadiene is one of the required monomers for EPDM rubber. Although iron-, cobalt-, and nickel-based Ziegler-type catalysts can codimerize butadiene and ethylene, the selectivity to the desired trans isomer is low. A soluble rhodium complex can, however, catalyze the dimerization with high selectivity to the trans isomer. 

These telomerization reactions of butadiene with nucleophiles are also catalyzed by nickel complexes. For example, amines (18-23), active methylene compounds (23, 24), alcohols (25, 26), and phenol (27) react with butadiene. However, the selectivity and catalytic activity of nickel catalysts are lower than those of palladium catalysts. In addition, a mixture of monomeric and dimeric telomers is usually formed with nickel catalysts ... 

Homogeneous nickel complexes proved to be versatile catalysts in dimerization and trimerization of dienes to yield different oligomeric products.46-55 Depending on the actual catalyst structure, nickel catalyzes the dimerization of 1,3-butadiene to yield isomeric octatrienes, and the cyclodimerization and cyclotrimerization to give 1,5-cyclooctadiene and all-trans-l,5,9-cyclododecatriene, respectively46 56 [Eq. (13.13)]. Ziegler-type complexes may be used to form cis,trans,trans-1,5,9-cyclododecatriene37,57 58 [Eq. (13.14)], which is an industrial intermediate ... 

Some insight into the nature of the coordination and addition steps can be deduced from the cyclo-oligomerization work reported by Wilke (316). Butadiene can be converted into several isomers of cyclododeca-triene using (C2H5)aAlCl/TiCl4, AlEta/Cr02Cl2 and AlEta/nickel acetyl-acetonate catalysts. With the nickel catalysts, open chain, jr-complexed intermediates have been isolated for both the butadiene trimer and the dimer. The open chain dimer structure is shown below, where Do = a bulky Lewis base and the nickel is apparently zero valent. 

In coordination polymerization it is generally accepted that the monomer forms a 7r-complex with the transition metal prior to insertion into the growing chain. In general these complexes are insufficiently stable to be isolated although complexes of allene [69] and butadiene [70] have been reported. With allene the complex was formed prior to polymerization with soluble nickel catalysts, and cis coordinated butadiene forms part of the cobalt complex, CoCj 2H19, which is a dimerization cateilyst. 

Nickel-based Ziegler catalysts are very effective for propylene dimerization.The unsupported catalyst is prepared by mixing NiCl2, Et3Al, and butadiene in chlorobenzene to yield a C12 7r-allyl complex of nickel. A phosphine is then added, followed by liquid propylene at 15 atm pressure. A mixture of n-hexenes, 2-methylpentenes, and 2,3-dimethylbutenes in 85-90% yield are produced rapidly at 30-40°C. Apparently this reaction is not reported for a polymer-bound version. This would be of interest since it is observed that the product distribution is quite sensitive to the nature of the phosphine. 

Although the linear dimerization of butadiene has been conducted with many catalyst systems, one of the best understood and most specific systems is the nickel(0)-tri-ethylphosphite-morpholine catalyst developed by Heimbach (Scheme 22.19). Coupling of butadiene by Ni(0) produces a bis-(-r -allyl) nickel complex. Protonation of an internal position of one of the T) -allyl groups by morpholine, followed by proton abstraction a to the other Tfj -allyl group, produces the observed octatrienes and regenerates the catalyst. 

Whereas nickel complexes catalyse the trimerization or dimerization of butadiene to cyclic products, palladium catalysts produce linear oligomers. When bis(dibenzoylacetone)palladium is treated with butadiene at low temperature, a yellow air sensitive complex (rj f/ -dodecatrienediyl)palladium is formed initially. It decomposes above — 20T in the absence of butadiene and in its presence actively catalyses its trimerization to linear 1, 3,6, 10-dodecatetraene. In contrast to the corresponding nickel intermediate, the substituents on the allyl groups are syn. Treatment with a diphosphine affords a metallacycle which contains a huge 13-membered ring. If (A) or (B) is allowed to warm above — 20 C or is treated with ligands (Ph P or CO), dodecatetraene isomers are released (Fig. 12.7). 

The telomerization reaction is catalyzed by various transition metal complexes as nickel, palladium or platinum, but among them, palladium catalysts proved to be the most efficient. With palladium catalysts, linear cis, trans and branched octadienyl ethers are the major products and side products that can arise from the linear dimerization or the degenerative telomerization of butadiene are formed in marginal amounts (Scheme 6). 

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