Oligomerization of 1,3-dienes

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. 

Olefin formation, by reductive elimination of 3-hydroxysulfones, 72, 2 Olefins, hydroformylation of, 56, 1 Oligomerization of 1,3-dienes, 19, 2 Oligosaccharide synthesis on polymer support, 68, 2 Oppenauer oxidation, 6, 5 Organoboranes ... 

Cyclo-co-oligomerization of 1,3-Dienes with Oleflns and Alkynes... 

The cyclo-co-oligomerization of 1,3-dienes with alkynes is characterized by the relative ease with which rings are formed and by the possibility of incorporation of more than one alkyne molecule (Scheme 6). 

The most widely used application of nickel-diene complexes is the dimerization of 1,3-dienes. Pioneering studies hy WiUce demonstrated many different modes of coupling, including dimerization, trimerization, and oligomerization of 1,3-dienes.l An overview of the product classes that maybe obtained from 1,3-dienes is provided in Scheme 4 (see also Houben-Weyl, Vol. E18, pp 93 and 932-937). The initially formed nickel complexes 5 and 6 have not been isolated. However, the complexes may be stabilized by the addition of phosphines, and jr-allyl complexes 7-9 have been prepared and characterized. 

The catalytic dimerization and oligomerization of 1,3-dienes can lead to a large number of linear or cyclic products by mechanistically related paths. The major product depends strongly on both the metal and the auxiliary ligands, and much is known about controlling the product distribution (see below). In this section, a few mechanistically well-characterized systems are discussed. For more details, see reviews on the subject. ... 

Palladium complexes, in contrast to nickel(0) catalysts (Section I,B,1), promote linear oligomerization of 1,3-dienes. These reactions are considered... 

Oligomerization of 1,3-dienes selectively yields four-, six- eight-, or twelve-mem-bered rings, depending on the nature of catalysts and reaction conditions [4,123]. Ni(COD)2-PPh3 catalyst has been shown to efficiently promote intramolecular cyclooctadiene formation in good yield from the corresponding bisdienes [124]. 

The catalytic cyclo-oligomerization of 1,3-butadiene mediated by transition-metal complexes is one of the key reactions in homogeneous catalysis.1 Several transition metal complexes and Ziegler-Natta catalyst systems have been established that actively catalyze the stereoselective cyclooligomerization of 1,3-dienes.2 Nickel complexes, in particular, have been demonstrated to be the most versatile catalysts.3... 

The catalytic cyclo-oligomerization of 1,3-butadiene was first reported by Reed in 1954 using modified Reppe catalysts.4 Wilke et al., however, demonstrated in pioneering, comprehensive and systematic mechanistic investigations, the implications, versatility and the scope of the nickel-catalyzed 1,3-diene cyclo-oligomerization reactions.3,5... 

As mentioned above, many transition metals catalyze the cyclooligomerization of 1,3-dienes. The nickel-catalyzed cyclooligomerization of BD, however, is probably one of the best-understood reactions in the field of homogeneous catalysis. In the 40 years since its discovery a mass of evidence has been collected, indicating that these oligomerizations are the result of a multistep addition-elimination mechanism at a nickel atom template, which constantly flips between two oxidation states. The following strategies played an important role isolation of key intermediates, simulation of the catalytic cycle in a stoichiometric manner, product analysis, and study of model compounds. Detailed analysis of the intellectual development of the mechanism is not included here as this can be followed from excellent reviews [6]. 

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. 

Let us briefly summarize the state of the art in the polymerization of other monomer groups in the presence of polymer-boxmd metal complexes. Considerable progress has been achieved in polymerization of dienes, namely, butadiene and isoprene, catalyzed by macromolecnlar complexes based on rare earth halides [114], Co-oligomerization of 1,3-butadiene and CO2 with immobilized palladium complexes (phosphynated PS as macromolecnlar ligand) [115] and polymerization of acetylene monomers with immobilized complexes of Mo(V), W(VI), and Pd(II) have been developed though they have not been investigated intensively. 

Nickel(O) complexes are extremely effective for the dimerization and oligomerization of conjugated dienes [8,9]. Two molecules of 1,3-butadiene readily undergo oxidative cyclization with a Ni(0) metal to form bis-allylnickel species. Palladium(O) complexes also form bis-allylpalladium species of structural similarity (Scheme 2). The bis-allylpalladium complexes show amphiphilic reactivity and serve as an allyl cation equivalent in the presence of appropriate nucleophiles, and also serve as an allyl anion equivalent in the presence of appropriate electrophiles. Characteristically, the bis-allylnickel species is known to date only as a nucleophile toward carbonyl compounds (Eq. 1) [10,11],... 

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 ... 

Treatment of methylenechloride solutions of 1,3-diazacyclonona-l,2-diene and 1,3-diaza-cyclotetradeca-1,2-diene with a catalytic amount of tetrafluoroboric acid affords mixtures of dimeric and oligomeric species. From the seven membered ring tricyclic carbodiimide generated in the thermolysis of tetrazolophenanthridene only its cyclodimer has been isolated. 

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