1,5-Cyclooctadiene metathesis

Cyclooctadiene, metathesis of, 135 stereoselectivity, 159, 160 Cyclooctene, metathesis of, catalysts for, 140... 

A chloro-substituted cycloalkene, 1-chloro-l, 5-cyclooctadiene, has also been converted by metathesis into a polymer, the perfectly alternating copolymer of butadiene and chloroprene (29). 

Mutual metathesis of a cyclic and an acyclic alkene provides still more possibilities in synthesizing organic compounds. For instance, cycloalkenes are cleaved by ethene into a,co-dienes. The reaction of 1,5-cyclooctadiene with ethene gives 1,5,9-decatriene (18) norbornene reacts with 2-butene to yield 1,3-dipropenylcyclopentane (30) ... 

By contrast, much of the work performed using ruthenium-based catalysts has employed well-defined complexes. These have mostly been studied in the ATRP of MMA, and include complexes (158)-(165).400-405 Recent studies with (158) have shown the importance of amine additives which afford faster, more controlled polymerization.406 A fast polymerization has also been reported with a dimethylaminoindenyl analog of (161).407 The Grubbs-type metathesis initiator (165) polymerizes MMA without the need for an organic initiator, and may therefore be used to prepare block copolymers of MMA and 1,5-cyclooctadiene.405 Hydrogenation of this product yields PE-b-PMMA. N-heterocyclic carbene analogs of (164) have also been used to catalyze the free radical polymerization of both MMA and styrene.408... 

In contrast to Ni, alkylpalladium precursors can be easily prepared and isolated owing to their greater stability (Scheme 2). The monomethyl chloride adducts of formula (diimine)PdMeCl can be conveniently synthesized via diimine displacement of other weakly coordinating ligands, such as COD from Pd(COD)MeCl (COD = 1,5-cyclooctadiene) [44], or by in situ alkylation-complexation with tetramethyltin [52], The chloride ligand can then be cleanly abstracted by metathesis with NaBAF... 

The presence of halogen atoms appears to exert little, if any, effect on catalyst activity, but it can influence the course of the metathesis reaction. Vinylic halides are unreactive, as exemplified by the ring-opening polymerization of l-chloro-l,5-cyclooctadiene, which afforded a perfectly alternating copolymer of butadiene and chloroprene (7/2) via polymerization exclusively through the unsubstituted double bond. 

Another system for transfer vinylation has utilized [Ir(COD)Gl]2 as the catalyst, and was applicable to the preparation of vinyl ethers from the reactions of aliphatic alcohols with vinyl acetate (COD = 1,4-cyclooctadiene Scheme 4).117 This protocol has been used for the preparation of chromenes by a vinylation-ring-closing metathesis sequence (Equation (19)).118... 

When the ruthenium Schiff base olefin metathesis catalyst was used to polymerize cyclooctadiene Mw s > 100,000 Da were obtained. Although only 12 Schiff bases were identified as effective in these polymerizations, additional analogs are anticipated to be reported from the University of Ghent group. 

Norbornadiene- and cyclooctadiene-containing bridged olefin metathesis catalyst were also prepared by the author in the current application and are illustrated below. 

II), on a mesoporous support having a hexagonal unit cell. The catalyst was used to prepare 5-norbomene and cyclooctadiene copolymers by ring-opening metathesis polymerization. 

Pawlow et al. (3) prepared multifiinctionalized high-trans-content elastomeric polymers using Grubbs second-generation ruthenium catalyst in the metathesis polymerization of cyclooctadiene, cyclopentene, and l,4-bis(trimethoxysilyl)-2-butene. 

Among cyclic polyenes, cyclic dienes, trienes and tetraenes have been ring-open polymerised via the metathesis reaction. Representative of the cyclodienes most commonly used for polymerisation are 1,5-cyclooctadiene, norbornadiene (bicyclo[2.2.1]hept-2,5-diene) and dicyclopentadiene as mono-, bi- and tricyclic diolefins respectively. Cycloocta-1,5-diene metathesis polymerisation is another approach to the preparation of 1,4-polybutadiene ... 

The Cope rearrangement was used in the total synthesis of (-)-asterisca-nolide (14), a novel sesquiterpene natural product4 (Scheme 1.4e). Ring-opening metathesis of the cyclobutene 15 with ethylene in the presence of the ruthenium catalyst 165 proceeded smoothly to provide the cyclooctadiene 18 via Cope rearrangement of the intermediate dialkenyl cyclobutane (17). 

The ruthenium catalyst RuCl2(= CHPh)(PCy3)2 is able to promote both alkene metathesis polymerization (ROMP) and atom transfer polymerization (ATRP) [80,81]. The bifunctional catalyst A was designed to promote both ROMP of cyclooctadiene (COD) and ATRP of methyl methacrylate (MMA). Thus, catalyst A was employed to perform both polymerizations in one pot leading to diblock polybutadiene/polymethylmethacrylate copolymer (58-82% yield, PDI = 1.5). After polymerization the reaction vessel was exposed to hydrogen (150 psi, 65 °C, 8h), under conditions for Ru(H2)(H)Cl(PCy3)2 to be produced, and the hydrogenation of diblock copolymer could attain 95% [82] (Scheme 36). 

The bridging chloride ligands in these [Ir(olefin)2Cl]2 compounds are susceptible to metathesis reactions, yielding new dimeric compounds of the form [Ir(olefin)2B]2 where B represents a new bridging ligand. AUcoxides, thiolates, and carboxylates have all been employed successfully in the replacement of chloride. The complexes with B = Br, I have also been prepared, both by metathesis reactions and by direct reaction of cyclooctene or cyclooctadiene with IrBrs or Iris The olefin complexes also provide excellent starting materials for the syntheses of arene and cyclopentadienyl iridium complexes, a subject that will be discussed in the next section. 

Very recently, Grubbs and coworkers completed an analysis based on insight from mechanistic work on the relative rates of phosphine dissociation and olefin coordination (vide infra) in ruthenium alkylidene catalyzed olefin metathesis reactions. The study was based on numerous analogues of (4a), having different phosphine groups, for example, (4e), (4f), and (4g). Rates for ROMP of cyclooctadiene with the most potent of these new complexes were 340-fold greater than with (4a) (Scheme 1) ... 

Catalyst Ru-4 exhibits overall superior activity and improved substrate scope relative to catalyst Ru-2. For example, Ru-4 completes simple metathesis reactions, such as the RCM of diethyl diallylmalonate or the ROMP of cyclooctadiene, at rates several orders of magnitude greater than with Ru-2. In addition, whereas catalyst Ru-2 is unreactive toward sterically congested or electronically deactivated substrates, Ru-4 successfully mediates the formation of tetra-substituted olefins in five- and six-mem-bered rings systems [9], as well as CM to form tri-substituted olefins and products containing electron-withdrawing substituents [10]. 

Ring-opening cross metathesis. Significant reactions belonging to this category are the formation of the cyclic acetals of l,4-alkadien-2-ones from cyclopropenone acetals and 1-alkenes, and the assemblage of 1,2-dialkenylcyclobutanes en route to complex 1,5-cyclooctadienes. 

Bis(phospholyl)zirconocene 282 was obtained as a 63 37 mixture of rac- and meso-isomers in the crude product from salt metathesis of a phospholyl anion and Z1CI4 in THF (Scheme 59).226 Washing the crude product with pentane enhanced the raclmeso ratio to 80 20, but a THF solution of this mixture reached back to the equilibrium ratio of 63 37 in <15 min, indicating facile isomerization processes among these diastereomers. Slow addition of a THF solution of ((R)-Kinap)RhlCOD)]OTf to a THF solution of 282 produced a single diastereomer of the bimetallic r -phosphazirconocene 283, which accomplishes the dynamic resolution of phosphazirconocene 282 (COD = 1,5-cyclooctadiene). 

The complex is also active in ring-opening metathesis polymerization of 1,5-cyclooctadiene (COD), where the ruthenium—carbene bond is now the initiating point. Therefore, a mixture of MMA and COD undergoes a dual or tandem living polymerization of both monomers to generate block copolymers of COD and MMA, which can be converted into ethylene-block-MMA copolymers on subsequent hydrogenation, also catalyzed by the complex. 

In 1998, Kempe and coworkers [34] reported the first aminopyridinato rare-earth metal complexes. 4-Methyl-2-[(trimethylsilyl)amino]pyridine(HLl) was utilized in this complex. The reaction of lithiated LI and YCI3 in ether and pyridine led to the ate complex [Y(Ll)4(LiPy)] (Py = pyridine) (1). The complex 1 catalytically mediated a ligand transfer reaction to form [Pd(Ll)2] and [Y(Ll)3(py)] (2) from [Pd(cod)Cl2] (cod = cyclooctadiene). The LI ligand transfer from yttrium to palladium and the regeneration of 1 are significant in the efficient synthesis of the very strained amido palladium complexes (Scheme 2). Lithiated LI underwent a salt metathesis reaction with ScCb, at low temperature in THF, to yield the homoleptic complex [Sc(L1)3] (3) (Scheme 2). 3 is the first reported scandium aminopyridinato complex [35]. 

As with all polycondensation reactions, the formation of cychc ohgomers by ADMET is possible and has been demonstrated in a variety of cases [31-33]. This occurs by intramolecular back-biting metathesis of an active metal carbene with an internal olefin of the polymer (Scheme 6.5) to hberate cyclooctadiene, for example, from ADMET polybutadiene, although larger cychcs have also been observed. A related undesired cyclization is the intramolecular cyclization of the monomer by RCM. 

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