Cyclooctene cross-metathesis

Conversions of about 80% were obtained within a few minutes at 90°C. The polymer could also be cleaved by cross-metathesis with an excess of 4-octene which gave, as the main product, 9-tridecenyl-7-undecenoate, thus confirming the structure assignment as indicated in Eq. (62). The unsaturated lactone was also copolymerized with cyclooctene, 1,5-cy-clooctadiene, and cyclopentene under the previously stated conditions to afford linear copolymers which were high molecular weight, unsaturated, rubbery polyesters (110). 

An example of the second category is the cross metathesis of cyclooctene and ethylene giving 1, 9-decadiene (60) in about 75% yield (Eqn. 22.55). 42 This reaction between cyclic olefins and ethylene provids an excellent method for the preparation of a, -diolefins. 2 ... 

Metathesis is a versatile reaction that forms the basis for several important industrial processes, such as the Phillips triolefin process, which produces propene by cross-metathesis of 2-butene with ethene, and the Shell higher olefins process (SHOP), which involves a combination process that converts ethene to detergent-range olefins. Several interesting polymeric materials are commercially produced via the ROMP of different types of unsaturated cyclic monomers, including nor-bornene, cyclooctene, and dicyclopentadiene [1]. 

Via stereoselective ethenolysis of 1,5-cyclooctadiene (COD), Bykov et al. [25] prepared l,d5-5,9-decatriene, a precursor for the synthesis of many ds-isomeric insect sex pheromone compounds. In the presence of the MoCl5/Si02/Me4Sn catalyst system, at 20 °C and an ethene pressure of 25 bar, a 80 % conversion of COD was obtained with a selectivity of 68.4% for l,ds-5,9-decatriene. From this triene, many long-chain (CiQ-Cig) unsaturated acetates, alcohols and aldehydes can be obtained with the required biologically active cis conformation. Cross-metathesis of cyclooctene with a-olefins in the presence of the same catalyst gave... 

The cross-metathesis of cyclopentene with imsymmetrical olefins is catalyzed by WOCl4/Bu4Sn or WOCl4/Et2AlCl. Herisson (1971) observed that the products of reaction with pent-2-ene consisted of three series of compounds Q M Q , Q M Q, and Q M Q (n = 1-4), where Q = ethylidene, = propylidene, and M represents n ring-opened units of cyclopentene M. These series were formed in the statistical ratio 1 2 1 even in the initial products. Similar results were obtained with cyclooctene, cycloocta-1,5-diene, and cyclododeca-l,5,9-triene in place of cyclopentene. It was these observations that led to the proposal of the metal carbene mechanism, since direct exchange between the double bonds of the reactant molecules would yield only the unsymmetrical series. The formation of the three series of compounds is accounted for in terms of reactions (l)-(6). 

A more stringent test is to react cyclooctene with a mixture of but-2-ene and oct-4-ene. If the metal carbene mechanism is correct, one may expect to find the C14 product of double cross-metathesis, i.e. MeCH=CH(CH2)6CH==CHPr, and an initial value of 4.0 for the product of the two ratios (C14/C12) and (C14/C16). The observed ratio is 4.05 0.05 for cis reactants and 4.11 0.09 for trans reactants (Katz 1977a). 

In cross-metathesis with symmetrical olefins only a single series of telomers can be formed. The transfer constants can then be determined directly from the relative rates of consumption of cyclic and linear olefins, making allowance for back reactions. For the cross-metathesis of cyclooctene with internal olefins, catalyzed by WCl6/Me2Si(CH2SiMe2CH2), Korshak (1982) obtained the following values for the transfer constants cw-but-2-ene 0.9, trans-but-2-ene 0.6, rra 5-oct-4-ene 0.2. 

Scheme 15.3 Mechanism of double cross-metathesis between cyclooctene (M), cw-but-2-ene (Q Q ) and ds-cot-4-ene (Q Q ).

One of the classical experiments in the development of olefin metathesis was the double cross metathesis in which a mixture of cyclooctene, 2-butene, and 4-octene underwent metathesis. 

High efficiency of the cross-metathesis of 1,9-decadiene and ROM/CM of cyclooctene with vinylsilanes points to a possibility of effective runs of the ADMET copolymerization of 1,9-decadiene [40] and tandem ROM/CM polymerization of cyclooctadiene [20], in both cases with divinylsilicon compounds. The reactions have proceeded according to Eq. 11, yielding polymeric material isolated and analyzed by GPC and NMR methods. 

Phillips also proposed a route to 1,9-decadiene by homogeneous hydrogenation of cyclooctadiene to cyclooctene and then cross-metathesis with ethylene over W03/Si02 (yield 75% for a conversion of 90%). 

In addition, the graft copolymer 2 may arise by competitive cross-metathesis of the PPO-AGE copolymer with the growing Ru-propagating species of the cyclooctene homopolymerization. The ratio between the two grafting processes depends essentially on the amount of Ru catalyst employed in this reaction. 

The metathesis reaction of cycloalkenes yields linear unsaturated polymers, so-called polyalkenamers. This ROMP is driven by the release of ring strain in the starting material. Several interesting polymers are commercially produced via the ROMP of different types of unsaturated cyclic monomers such as cyclooctene, norbornene, and dicyclopentadiene, using homogeneous catalyst systems [6]. As an alternative process, the cross-metathesis between a cyclic and an acyclic olefin allows to synthesize certain poly-unsaturated compounds for the special chemical market. Shell [7] developed the FEAST process for the manufacture of hexa-l,5-diene via cross-metathesis of cycloocta-1,5-diene with ethene. 

The first report of NHC-containing osmium compounds acting as catalysts came from Esteruelas and co-workers in 2005. Thus, cationic benzyli-dene complexes 44 were prepared by reaction of the corresponding 16-electron precursors [(NHC)OsCl(p-cymene)][OTf] (NHC = IMes or IPr) with phe-nyldiazomethane, and their potential as initiators for olefin metathesis was probed in the RCM of diethyl diallylmalonate, the ROMP of cyclooctene, and a variety of self- and cross-metathesis reactions (Equation (7.10)). Although they were not as efficient as standard ruthenium-benzylidene metathesis initiators, compounds 44 displayed, nevertheless, a fairly decent activity. More importantly, in addition to being the first NHC-Os catalytic application, this study constituted a rare example of osmium catalysed C-C bond formation. 

Polymers of monocyclic olefins (cyclopentene, cyclooctene) produced by ring-opening metathesis are linear elastomers. Their properties are somewhat similar to those of poly eri-1,4-hn i.idiene). Polymers of dicy-clopentadiene produced with the same catalysts are heavily cross-linked resins displaying high toughness and tensile strength as well as excellent impact strength at low temperatures. 

When cyclic alkenes are utilized as starting materials the metathesis reaction will lead to long chain polymers and/or cyclic oligomers [103, 104, 107, 108]. If a strained cyclic alkene is employed the reaction is effectively irreversible. Industrially cyclooctene (polymer Vestenamer), 2-norbornene (polymer Norsorex), and dicyclopentadiene (polymer Telene, Metton, Pentam) are used as monomers. Upon polymerization cyclooctene and 2-norbornene yield straight chain polymers while dicyclopentadiene also allows cross-linking (Scheme 5.56). 

The ROMP of cyclooctene-5-methacrylate and its copolymerization with cyclooctadiene is catalyzed by Ru(=CHCH=CPh2)(Cl)2(PCy3)2 in the presence of p-methoxyphenol as radical inhibitor. The double bonds in the methacrylate groups are inert towards metathesis. After chain transfer with ethyl vinyl ether to release the polymer from the ruthenium centre, it can be cross-linked by radical polymerization through the methacrylate side-chains (Maughon 1995). 

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