Oligomerization of Butadiene

Thus it becomes unlikely that 7 can exist long enough to allow extensive dimerization or oligomerization of butadiene. It has also been speculated (7, 9) that the presence of coordinated chlorides on the Rh complex prevents the occurrence of butadiene polymerization reaction. 

Figure 3 in Scheme 2.3-2 illustrates that Ni- or Pd-complexes prefer a different combination of elementary steps. Here, it is evident that Ni favors 2 1 co- oligomerization of butadiene with tddehyde or of a Schiff base with butadiene involving C -bond formation coupled with metalalogous 1,5-hydrogen transfer. On the other hand, Pd favors 0—C- or N—C- andC—C-bond formation. These processes seem to occur more frequently, as demonstrated by other catalytic processes and model reactions . ... 

Linear dimerization and oligomerization of butadiene can be achieved by using a number of catalyst systems based on Pd, Ni (158—161), and Fe (162). 1,7-Octadiene can be obtained selectively when the dimerization is carried out in the presence of a reducing agent such as formic acid (163—165) or... 

When some other reaction parameter, Z, such as the log of a rate constant, is plotted on to this steric and electronic map on an axis normal to the plane of the paper the comparative contributions of 6 and v should become apparent. A purely steric effect will slope north or south (the reader is encouraged to view Figures 26-28 of ref. 187 to appreciate this fully). Weimann and co-workers211 used Tolman s methodology to show the % steric effect in the oligomerization of butadiene catalyzed by nickel phosphine complexes. 

A variation, which has the advantage that the rate of reaction may be increased, is to use a catalyst which normally converts butadiene into COD, i.e., the Ni-ligand system. At the same time this introduces the disadvantage that COD and VCH are also produced. The effect of varying the ligand on the co-oligomerization of butadiene and ethylene is summarized in Table IX. 

Co-OLIGOMERIZATION OF BUTADIENE AND ETHYLENE USING A NlCKEL-LlGAND CATALYST 6... 

A reasonable mechanism for the co-oligomerization of butadiene with ethylene on a naked-nickel catalyst is shown in Eq. (49). Interaction of an ethylene molecule with the bis(7r-allyl) C8 chain produces a C,0 chain, containing both an alkyl- and a 7r-allylnickel group (XLVI). Coupling of the alkyl bond with the terminal atom of a m-Tr-allyl group or the terminal... 

Immediately after the discovery of the cyclodecadiene synthesis by the co-oligomerization of butadiene and ethylene, the question of whether other unsaturated systems could be used in place of ethylene was investigated. Of the many variations on this theme which have been studied (92, 93), we will limit ourselves to discussing the co-oligomerization of 2-butyne, since this system became a model for all the other combinations. 

The effect of various ligands on the yield of DMCDeT is illustrated in Table X and should be compared with the cyclodimerization of butadiene and the co-oligomerization of butadiene with ethylene (Tables III and IX). 

Fig. 3. Volume contraction in the co-oligomerization of butadiene with 2-butyne (nickel-ligand catalyst) (94) I = P(C6H5)3, II = P(OC6H5)3.

The structure of the product (LXI) obtained by co-oligomerization of butadiene, sorbic ester, and ethylene also supports the suggestion that it is the methyl-substituted carbon atom of sorbic ester which couples to the butadiene. Compound (LXI) is formed in over 80% yield (102). 

We have already mentioned that the co-oligomerization of butadiene with ethylene leads to the formation of decatriene (DT) by a hydrogen-transfer process. The ratio of cyclized to open-chain product depends on the temperature and the nature of the ligand bonded to the nickel. An additional factor which affects the product distribution is the presence and nature of substituents on the olefin. Aryl and ester groups are particularly effective in promoting a hydrogen-transfer reaction, and are treated in detail below. 

What compounds are the active catalysts in this process By this method of catalyst preparation we do not obtain a mixture of indefinite composition, but TT-complexes which can be isolated and are mostly crystalline. If, for instance, nickel acetylacetonate is reduced in the presence of P(CeH5)3 we obtain a new compound, Ni-(0)-[P(CeH5)3]4. This compound is itself an active catalyst for the cyclo-oligomerization of butadiene, producing about 65 to 70% cyclo-octadiene, 20% vinylcyclohexene, and 10% cyclododecatriene. Instead of P(CeH5)3 we can introduce As(CeH5)3 and isolate Ni-(0)-[As(CeH5)3]4 as an active cata-... 

Pentose-based surfactants have also been obtained through Pd-catalyzed oligomerization of butadiene [27-29]. This aspect is developed in Palladium-catalyzed telomerization of butadiene with polyols from mono to polysaccharides devoted to this type of products. 

Oligomerization of Butadiene. Butadiene is dimerized by Pd(0) complexes with... 

This leads us to propose a theoretically verified, refined catalytic cycle for production of linear and cycHc CiQ-olefin products (cf. Scheme 3). Furthermore, a detailed comparison of crucial mechanistic aspects of the catalytic reaction course for co-oligomerization of butadiene and ethylene and for cyclooligomerization of butadiene promoted by zerovalent bare nickel complexes was undertaken. These contribute (first) to a more detailed understan(fing of mechanistic aspects of the [Ni"]-mediated co-oHgomerization of 1,3-dienes and olefins and (second) to a deeper insight into the catalytic structure reactivity relationships in the transition-metal-assisted co-oHgomerization and oligomerization reactions of 1,3-dienes. 

This reaction may be achieved by the use of two monofunctional catalysts (hydroformylation and hydrogenation) or one bifunctional catalyst (chloromethyl-ated CSDVB, modified by secondary amino groups with bound RhCl(PPh3)2(CO)) (Fig. 12-13). The rates of the first, second and third stages of the bifunctional catalyst are 5-, 15- and 30-fold higher respectively than those of the two monofunctional immobilized catalysts. We should also mention the oligomerization of butadiene with the hydroformylation of vinyl cyclohexene by Ni-Rh complexes bound to phosphorylated CSDVB and the preparation of 4-methyl-2-pentanone on polymer-immobilized heterometallic complexes, etc. 

The nickel(o)-catalysed oligomerization of butadiene has been further studied. Cyclo-octa-1,5-diene is a major product in hydroxylic solvents, and a minor product in the presence of secondary amines." The oligomerization of butadiene in the presence of nickel(ii)acetylacetonate, triethylamine, alkyl cyanamides, and miscellaneous heterocycles has also been studied, and catalyst systems causing an almost quantitative conversion into trans,trans,trans-, cis,trans,trans-, or cis,cis,trans-cyclododeca-l,5,9-triene were found." The ability of some hydrides, trans-MHX-(PR3)2 (M = Ni or Pd), to act as catalysts for butadiene oligomerization has been found to depend upon the substituent, X, and the solvent the reactions of some cationic palladium hydrides with butadiene was also examined. Unlike other organo-cobalt catalyst systems, CoCUPPhjjj has been found to catalyse the dimerization... 

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