Co-oligomerization

Tindall D,PawlowJH,Wagener KB (1998) RecentAdvancesin ADMET Chemistry. 1 183-198 Tobisch S (2005) Co-Oligomerization of 1,3-Butadiene and Ethylene Promoted by Zerovalent Bare Nickel Complexes. 12 187-218 Tomioka K, see Iguchi M (2003) 5 37-60 Tomooka K, see Hodgson DM (2003) 5 217-250... 

Simmons KE, RD Minard, J-M Bollag (1989) Oxidative co-oligomerization of guaiacol and 4-chloroaniline. Environ Sci Technol 23 115-121. 

Inspired by the well-established nickel-catalyzed co-oligomerization of 1,3-dienes with CO2, which proceeds via bis-TT-allyl intermediate, Mori has developed a powerful intramolecular version of this process (Scheme 103). After insertion of C02 into the bis-vr-allyl complex, a transmetallation with an organozinc reagent takes place to generate the Ni(0) catalyst. Highly functionalized carbo- and heterocyclic compounds with complete stereocontrol can372 be synthesized by this method. 

The cobalt catalyzed cocyclization of alkynes with heterofunctional substrates is not limited to nitriles. cpCo-core complexes are capable of co-oligomerizing alkynes with a number of C,C, C,N or C,0 double bonds in a Diels-Alder-type reaction. Chen, in our laboratories, has observed that these cycloadditions are best performed with the help of stabilizers such as ketones or acetic esters that are weakly coordinated to the cobalt and prevent the alkynes from being cyclotrimerized at the metal center... 

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 . ... 

In the co-oligomerization of w-systems, DO/ACC-perturbatlons of substrates (Houks X- and Z-substituents) play a significant role (for the perturbation induced by Houks C-type substituents see Ref. ). The following two aspects will be discussed ... 

DO- or ACC-perturbations in one of two rr-systems can change the molecular ratio in the co-oligomerization of these tr-systems. 

The invaribiiity of co-oligomer (12) against a variation of the ([L]o/[M]q) ratio ai erts an independent way for its generation. A preliminary scheme for the additionally formed intermediate complexes of the co-oligomerization is given on page 87. 

Such a capability of an oligonucleotide system deserves special attention in the context of the problem of the origin of biomolecular homochirality breaking molecular mirror symmetry by de-racemization is an intrinsic property of such a system whenever the constitutional complexity of the products of co-oligomerization exceeds a critical level. 

Figure 45. Synthesis of oligo[2]catenanes by co-oligomerization according to Mullen et al.

The mechanism of the unprecedented chromium-catalysed selective tetramerization of ethylene to oct-1-ene has been investigated. The unusually high oct-1-ene selectivity of this reaction apparently results from the unique extended metallacyclic mechanism in operation. Both oct-1-ene and higher alk-l-enes were formed by further ethylene insertion into a metallacycloheptane intermediate, whereas hex-1-ene was formed by elimination from this species as in other trimerization reactions. Further mechanistic support was obtained by deuterium labelling studies, analysis of the molar distribution of alk-l-ene products, and identification of secondary co-oligomerization reaction products. A bimetallic disproportionation mechanism was proposed to account for the available data.120... 

The formation of CDT is suppressed if ethylene as well as butadiene is brought into contact with a naked-nickel catalyst. Depending on the reaction conditions, the product is a mixture of m,tram-1,5-cyclodecadiene (CDD) and 1,tram-4,9-decatriene (DT) (90). With equal concentration of butadiene and ethylene the co-oligomerization occurs some six times faster than the cyclotrimerization of butadiene to CDT. 

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. 

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