2,6-Octadiene metallation

The cycloaddition between norbornadiene (23 in Scheme 1.12) and maleic anhydride was the first example of a /mmo-Diels-Alder reaction [55]. Other venerable examples are reported in Scheme 1.12 [56]. Under thermal conditions, the reaction is generally poorly diastereoselective and occurs in low yield, and therefore several research groups have studied the utility of transition metal catalysts [57]. Tautens and coworkers [57c] investigated the cycloaddition of norbornadiene and some of its monosubstituted derivatives with electron-deficient dienophiles in the presence of nickel-cyclo-octadiene Ni(COD)2 and PPhs. Some results are illustrated in Tables 1.4 and 1.5. 

Scheme 43 Synthesis of enantiopure ring-substituted 1,2-diaminocyclohexanes by transition metal catalyzed and promoted cyclization of 1,7-octadienes...

Among many examples of -orbital interaction, only the following two are selected to illustrate the feature of HO—LU conjugation. One is the cyclooctadiene-transition metal complex ">. The figure indicates the symmetry-favourable mode of interaction in a nickel complex. The electron configuration of nickel is (3d)8 (4s)2. The HO and LU of nickel can be provided from the partly occupied 3d shell from which symmetry-allowed occupied and unoccupied d orbitals for interaction with cyclo-octadiene orbitals are picked up. 

Another recent application to the activation of transition metals was reported (247) by Bonnemann, Bogdavovic, and co-workers, in which an extremely reactive Mg species was used to reduce metal salts in the presence of cyclopentadiene, 1,5-cyclo-octadiene, and other ligands to form their metal complexes. The reactive Mg species, characterized as Mg(THF)3 (anthracene), was produced from Mg powder in THF solutions containing a catalytic amount of anthracene by use of an ultrasonic cleaning bath. A plausible scheme for this reaction has been suggested ... 

As mentioned above, gas-phase coordination of unsaturated C—C bonds to metal cations constitutes another means for double-bond localization. Peake and Gross260 determined the fragmentation of Fe+/olefin complexes by CID spectrometry and reported highly characteristic differences for several constitutional octadiene isomers. High-resolution mass spectrometry proved to be necessary in certain cases due to the isobaric masses of Fe and even two units of C2H4 and/or CO261. Although not based on gas-phase ion/molecule... 

The metal-catalysed autoxidation of alkenes to produce ketones (Wacker reaction) is promoted by the presence of quaternary ammonium salts [14]. For example, using copper(II) chloride and palladium(II) chloride in benzene in the presence of cetyltrimethylammonium bromide, 1-decene is converted into 2-decanone (73%), 1,7-octadiene into 2,7-octadione (77%) and vinylcyclohexane into cyclo-hexylethanone (22%). Benzyltriethylammonium chloride and tetra-n-butylammo-nium hydrogen sulphate are ineffective catalysts. It has been suggested that the process is not micellar, although the catalysts have the characteristics of those which produce micelles. The Wacker reaction is also catalysed by rhodium and ruthenium salts in the presence of a quaternary ammonium salt. Generally, however, the yields are lower than those obtained using the palladium catalyst and, frequently, several oxidation products are obtained from each reaction [15]. 

Hence, two methods are available that can be applied to follow nanoparticles formation and growth (i) an indirect method that utilizes the consumption of molecular hydrogen pressure versus time and (ii) a direct method that follows the loss of precursor by the 1 1 conversion of its cyclo-octadiene ligand to cyclo-octane by GLC measurements. The mechanism developed by Watzky and Finke suggests that the nanoparticles act as Hving-metal polymers -a concept that could be used to obtain particles with defined sizes simply by adding the appropriate amounts of catalyst precursors [32]. 

This equilibrium was first studied by Cope et a .54 in 1952. The Gibbs energy difference is small and the rate of interconversion slow at room temperature. Huisgen et al.55 examined the influence of variations of the ethane fragment on the position of the equilibrium. Attachment of a tricarbonyliron moiety apparently causes stabilization of the bicyclo[4.2.0]octadiene system,56 whereas with tricarbonylmolybdenum the monocyclic isomer is isolated as its metal complex.57... 

Abbreviations arene, i/6-benzene or substituted benzene derivative bipy, 2,2 -bipyridyl Bu, Bu", Bu, iso-, n-, or rerf-butyl COD, 1,5-cyclo-octadiene Cp, /5-C5H5 DAD, dimethyl-acetylene dicarboxylate dam, 1,2-bis(diphenylarsino)methane DBA, dibenzylideneacetone DMF, A. A -dimethylformamide dpe, l,2-bis(diphenylphosphino)ethane dpen, os-l,2-bis(di-phenylphosphino)ethylene dpm, 1,2-bis(diphenylphosphino)methane ESR, electron spin resonance F6-acac, hexafluoroacetylacetone FN, fumaronitrile MA, maleic anhydride Me, methyl MLCT, metal ligand charge transfer phen, 1,10-phenanthroline Pr , Pr", iso- or n-propyl py, pyridine RT, room temperature TCNE, tetracyanoethylene tetraphos, (Ph2PCH2CH2)jP THF, tctrahydrofuran Xylyl, 2,6-Me2C6H3. 

Various metal acetylides are used for smooth coupling with propargylic halides and acetates. 2,3-Alkadien-5-yn-l -ols are obtained by the reaction of 2-(l -alkynyl)oxiranes [28,29], As a synthetic application, the unstable 2,3-octadiene-5,7-diyn-l-ol (136), a fungus metabolite, has been synthesized by the coupling of 4-trimethylsilylbutadiy-nylzinc chloride (134) with 2-ethynyloxirane (135) followed by desilylation [31]. 

Diene and, especially cyclodiene complexes (together with arene compounds) are the most explored organometallic ligands. The above-mentioned method of direct (immediate) interaction of reactants is also used to prepare their complexes. As a source of metal center, PtCl2 (3.62) and K2[PtCl4] (3.63) are applied in reactions with cyclo-octadiene-1,5 (COD) [11] ... 

The electrochemical technique has been relatively rarely applied to obtain the metal 7i-complexes [202,506,507], Thus, the electrosyntheses of complexes of copper with cyclo-octadiene and nickel with cyclo-octatetraene were reported [202,506,507]. The electrochemical reactions (3.242) are of especial interest, since they allow us to produce fe-cyclopentadienyl complexes [563-565] ... 

In general, the telomerization reaction is defined as the dimerization of two molecules of a 1,3-diene in the presence of an appropriate nucleophile HX to yield substituted octadienes [216,217]. This reaction allows us to assemble simple starting materials in a 100% atom efficiency [218] and to easily prepare useful intermediates in the total synthesis of natural products [219,220] and industrial precursors [221], In light of numerous studies, the mechanism of the palladium-catalyzed telomerization reaction is well understood [222,223]. It is accepted that one strongly bound and sterically hindered ligand on the metal center is desirable to generate highly active species, characteristics fulfilled by (NHC)-Pd(O) complexes. 

Scheme 7.6 Preparation of 1,5-cy clo octadiene (1,3,5-cycloheptatriene) and 1,5-cyclooctadiene(l,3,5-cyclooctatriene) metal(O) complexes via the isopropyl Grignard method (25, 27 ...

With AgC104, 1,5-hexadiene, 1,7-octadiene, and 1,9-decadiene form 3 2, 1 1, and 1 1 complexes, respectively (85a). The 1 1 complexes are considered (85a) to be coordination polymers while the 3 2 complex of 1,5-hexadiene has been shown (45a) to have chelated diene-silver ion entities connected through a bridging diene molecule to produce a distorted trigonal coordination about the metal. 

As noted above (Section IV.B.5) various metal complexes including Ni(0)(cyclo-octadiene)2 catalyse cyclopropene ring cleavage reactions and deliver products by way of... 

Thermal cyclooligomerizations of olefins and alkynes require severe and often dangerous reaction conditions and the yields of cyclic products are usually very low. Acetylene ean be trimerized to benzene at 500 °C [1] and butadiene (BD) dimerizes at 270 °C and under high pressure to give small amounts of 1,5-cyclo-octadiene [2]. Reppe s discovery in 1940 that acetylene can be cyclotetramerized to cyclooctatetraene (COT) using a nickel catalyst [3] shows that transition metals can act as templates for the synthesis of cyclic hydrocarbons from acetylenic or olefinic building blocks (Scheme 1). 

In the case of Ni, metallacyclic compounds containing the divalent metal may be obtained by alkene dimerization. Not only does this reaction occur with electron-deficient or strained alkenes, but under suitable conditions ethene or 1,7-octadiene reacts to give nickelacyclopentane species ... 

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