Cyclooligomerization 1,3-dienes

In the course of developing the diene cyclooligomerization and hydrogenation catalysts described above, we recognized that soluble polymers could also be used in such multi-step processes. However, unlike the case with two different polystyrene-bound species, the use of one soluble and one insoluble polymer bound species would enable the facile isolation of the product and each catalyst or reagent. Flotation techniques can be used to separate two insoluble polymers from one another. However, separation of a soluble polymer from an insoluble one would be simpler since it would only involve a filtration step. Kinetic isolation of each polymer-bound species would be possible even with one soluble polymer-bound species because of the diffusional constraints associated with soluble macromolecules. 

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... 

These catalysts should be clearly distinguished from those active for the cyclooligomerization of conjugated dienes, etc., which are based on zero-valent nickel compounds... 

The r/5-cyclopentadienylcobalt unit, [Co(t/5-C5H5)], is believed to be a key active species in catalytic cyclooligomerization of acetylenes or cooligomerization of acetylenes with other unsaturated reactants. It can be generated from several precursors, [Co( /5-CjH5)(CO)2],1 [Co(t/5-C5H5)(t/4-diene)],2... 

Cyclooligomerization. Ever since the first cyclodimerization reaction of 1,3-butadiene to yield 1,5-cycloctadiene catalyzed by a so-called Reppe catalyst was reported45 [Eq. (13.12)], cyclooligomerization of conjugated dienes has been intensively studied ... 

It is appropriate to include here two bis(T)3-allyl)nickel complexes that are formed by reacting zerovalent nickel species with 1,3-dienes and that have been shown to be involved as intermediates in the nickel-catalyzed cyclooligomerization of butadiene, viz., (T)3,i73-C12H18)Ni and (rj3-QH NiPRa. 

Telomerization reactions of dienes are important. While cyclooligomerizations of butadienes with nickel catalysts are technically important for producing the precursors of polyamides or polyesters (cf. Section 2.3.6), the telomerization... 

The first catalytic cyclodimerization of 1,3-butadiene (BD) to 1,5-cycloocta-diene using modified Reppe catalysts was reported by Reed in 1954 [4], and only two years later Wilke reported on the titanium-catalyzed synthesis of cyclo-dodecatrienes from BD [5]. It remained for Wilke and his co-workers to show the tremendous versatility and scope of the nickel-catalyzed cyclooligomerizations of... 

The cyclooligomerization reaction is not confined to BD as the monomer. Activated or monosubstituted 1,3-dienes also react, but reaction rates are usually slow, and selectivity and turnover numbers (TONs) are low. Cyclotrimerization and cyclodimerization of substituted 1,3-dienes - either alone or in admixture with BD - give numerous isomers of substituted CDT, COD, VCH and divinyl-cyclobutane (DVCB). For example, isoprene [34], 1,3-pentadiene [35], 2,3-dimethylbutadiene [36], 1,3-hexadiene [37], and even 1-vinyl-1-cyclopentene [38] do react (eqs. (2)-(6)). 2,4-Hexadiene is inert. 

Many transition metals catalyze oligomerization reactions between dienes and olefins or alkynes. Possible reaction products are legion. But it is almost exclusively with zerovalent nickel that cyclic products are formed. Addition of olefins or alkynes to catalysts mentioned in the previous section suppresses the cyclooligomerization and instead gives cyclo-co-oligomerization products. 

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]. 

Enantioselective cyclooligomerizations of butadiene can also be achieved when a chiral diaza-diene-iron(II) chloride complex and a fourfold excess of ethylmagnesium iodide are used. Optical yields of 9 to 16% are obtained with two chiral diazadienes of the type R N = CRCR = NR, prepared by formic acid catalyzed condensation of aqueous glyoxal (R1 = H) or 2,3-butadione (R1 = CH3) with (R)-l-phenylethylaminc or (1S,2S,3S,5R)-3-(aminomethyl)pinane. The (di-azadienc)iron(0)-catalyzed dimerization of butadiene also gives 4-vinylcyclohexene with up to 16% ee60. 

Similar to cyclodimerizations, transition metal catalyzed cyclooligomerizations and cocyclooligomerizations involve dicarborative addition steps. The most important examples of this type are represented by cyclotrimerization and cyclotetramerization of alkenes. dienes, alkynes and systems with hetero multiple bonds, leading to carbocyclic and heterocyclic six-, eight- or twelve-membered rings1 ... 

The oligomerization and cyclooligomerization of dienes is a synthetically useful and commercially significant reaction catalyzed by transition-metal complexes from different triads. In nearly all examples, -allyl complexes are intermediates, formed by either coupling of dienes about a metal template or by insertion of the diene into a metal-H bond. Allyl complexes are isolated from stoichiometric and catalytic diene oligomeriza-... 

Abstract The transition-metal-catalyzed cyclooligomerization of 1,3-dienes and the cooligomerization of 1,3-dienes and alkenes, that involve the stereoselective formation of carbon-carbon bonds, are of great interest from both a scientific as well as an industrial point of view. In this account a theoretical well founded, comprehensive mechanistic view of the [Ni ]-catalyzed co-oUgomerization of 1,3-butadiene and ethylene is presented. The... 

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. 

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