Cycloocta-1,5-diene complexes

Substituted cycloocta-1, 5-diene complexes of CpCO and CpRh. (MW). 

The mass spectra of the cycloocta-1,5-diene complexes C5H5MC8H12 (M = Rh, Ir) both show the molecular ion as the base peak. The rhodium complex exhibits several metastable peaks and a detailed fragmentation scheme has been proposed. The molecular ion fragments by several... 

However, the usual course of events in the isomerization of cycloalkadienes is to achieve conjugation where coordination is impossible. Thus cyclohexa-1,4-diene is isomerized to cyclohexa-1,3-diene by [RuC PPhsjs]. Nevertheless, RhCb 3H2O isomerizes cycloocta-1,3-diene, the most stable isomer, to a chelated cycloocta-1,5-diene complex (equation 6). Since no intermediate cycloocta-1,4-diene can be observed in the reaction, it was presumed to proceed via an... 

Note In the original procedure, the cycloocta-1.5-diene complex [CgHi2RhCl]2 was used as starting material. The present method avoids the isolation of the intermediate [Rh(PMe3)4]Cl. 

According to the MO treatment, all duroquinone complexes should have a singlet ground state and should be diamagnetic. This has been confirmed by experiment. However, the cycloocta-1,5-diene complexes of Ni with 2,5- or 2,6-dimethylquinone are paramagnetic in the solid state with moments of 1.5 and 2.75 B.M., respectively 64). If it is assumed that the total wave function for these complexes already contains ionic contributions, as indicated by (XXXI), it is probable that intramolecular oxidation takes place, causing the observed magnetic moments. 

Treatment of [Cp Ru(Ti -C4H6)(X)] (X = Cl, Br) with excess buta-l,3-dicne in the presence of silver trifluoromethanesulfonate (AgOTf) followed by carbon monoxide afforded OS the cycloocta-1,5-diene complex [Cp Ru(Ti -COD)(CO)]+[(OTf)], by means of a (4 + 4] cycloaddition reaction. Similar dimerisation, both stoichiometric and catalytic, was observed with other conjugated dienes. 

Significant advances in organonickel chemistry followed the discovery of frtzws,fraws,fraws-(l,5,9-cyclododecatriene)nickel, Ni(cdt), and bis(l,5-cycloocta-diene)nickel Ni(cod)2 by Wilke et. al.1 In these and related compounds, in which only olefinic ligands are bonded to the nickel, the metal is especially reactive both in the synthesis of other compounds and in catalytic behavior. Extension of this chemistry to palladium and to platinum has hitherto been inhibited by the lack of convenient synthetic routes to zero-valent complexes of these metals in which mono- or diolefins are the only ligands. Here we described the synthesis of bis(l,5-cyclooctadiene)platinum, tris(ethylene)-platinum, and bis(ethylene)(tricyclohexylphosphine)platinum. The compound Pt(cod)2 (cod = 1,5-cyclooctadiene) was first reported by Muller and Goser,2 who prepared it by the following reaction sequence ... 

These have previously been obtained by electrophilic attack on ene-yl complexes [equation (a) Y = CH(C02Me)2, OMe ch = 1J-C5H5 diene = 1,5-cyclooctadiene]1 or by reaction of the compounds (diene)MBr2 with 57-C5H6Fe(CO)2Br (diene = 1,5-cyclooctadiene or 1,2,3,4-tetraphenyl-l,3-cyclobutadiene).2 An example of the former method is given in which the methoxy-cyclooctenyl derivative is used as the substrate and tetrafluoro-boric acid as the electrophile. The substrate is conveniently prepared and used without isolation, and in this way the reaction takes only a few hours, starting with dichloro(l,5-cycloocta-diene)palladium, prepared as described above. 

The complex has enjoyed relatively little use in organic synthesis. For iridium-catalyzed homogeneous hydrogenation of alkenes, Crabtree s iridium complex ((1,5-Cycloocta-diene)(tricyclohexylphosphine)(pyridine)iridium(I) Hexafluoro-phosphate) is generally preferred, although this readily prepared Ir complex is active. It is more reactive than its rhodium counterpart in the catalytic isomerization of butenyl- to allylsilanes. ... 

Stable olefin-Ni(O) complexes are formed also with 1,5-cycloocta-diene (COD) and cyclooctatetraene (COT), by displacement of cyclo-dodecatriene from (Ci2Hig)Ni (608) or by reduction of nickel acetyl-acetonate (73). The COD complex has also been produced (419) by treating anhydrous NiClg with an excess of iso-C3H7MgBr and COD in ether under UV irradiation. 

Schrauzer and Thyret have described (528, 529, 531) the synthesis of olefin-Ni(O) complexes containing a quinone, in particular, duro-quinone, as a ligand. The red, diamagnetic duroquinone complexes are obtained by reaction of nickel carbonyl with the quinone in excess olefin. They are stable in air and soluble in polar organic solvents and water. Those olefins which form the coiiqilex contain essentially parallel double bonds, e.g., norbornadiene, dicyclopentadiene, 1,5-cycloocta-diene, 1,3,5-cyclooctatriene, or cyclooctatetraene. 

In addition to the design of the solubility properties, the reactivity of organome-tallic species toward CO2 [13] (and many other potential supercritical reaction media) must be considered as important criteria for the choice of the catalyst. For example, the bisallyl ruthenium complex shown in Table 1 cannot be utilized as a precursor for ring-opening metathesis polymerization (ROMP) in SCCO2, because the insertion of CO2 into the Ru-allyl bond prevents the initiation mechanism [14]. Metal-mediated oxygen transfer to form CO and phosphine oxide was found to lead to deactivation of the [Ni(cod)2]/PMe3 (cod = 1,5-m-cycloocta-diene) catalyst system [15]. On the other hand, the reactivity of CO2 with metal... 

Decomposition of the CU2X2 complexes left as residues from such illuminations produced cis,cis-1.5-cyclooctadiene, cis,trans-1.5-cycloocta-diene, and small amounts of trans,trans-1.5-cyclooctadiene (33). (33) gives (32) on illumination 522>. However, is it not yet clear whether free (33) is formed in cyclooctadiene photolysis, and then undergoes rear-... 

Reagents. The lithium metal, containing a maximum of 0.05% sodium, was obtained from the Lithium Corporation of America. Bis(l,5-cycloocta-diene)nickel [(Cod)2Ni)] was prepared by a modification of a known procedure (13). This complex was used to prepare tetrakis(triethylphosphine)nickel [(Et3P)4Ni]. Tetraphenylcyclobutadienenickel(II) bromide dimer was synthesized from stilbene-free diphenylacetylene (14). 

The high reactivity of nickel-diene complexes, which renders them very useful in catal5d-ic applications, makes their isolation quite difficult in most cases. The few cases in which nickel-1,3-diene complexes (e.g., 4) have been isolated generally involve displacement of a ligand with a low binding constant such as cyclooctadiene. This should, in theory, be possible using nickel(II) salts reduced in situ, although bis(q -cycloocta-l,5-diene)nickel(0) or (Ti -cyclododeca-l,5,9-triene)nickel(0) (Scheme 3 cdt = cyclododeca-l,5,9-triene) are typically employed.l 1... 

Chiral (E)-enolethers. A degassed soln. of (5R)-5-cyclohexyl-2-ethenyl-l,3-dioxolan-4-one (2 1 cisjtrans) in THF added to ca. 1 eq. of a suspension of bis(l,5-cycloocta-diene)nickel(0) in the same solvent under N2, stirred until the complex dissolved (10 min), after 3h the resulting rust-coloured precipitate collected, suspended in methylene chloride, treated with MejSiCl, and stirred for 30 min intermediate 7c-allylnickel complex (Y 78%), in benzene treated with DMF and 5 eqs. 1-iodo-propane, irradiated with a sunlamp (GE 275 W Model RSW) for 2,5 h at 10°, stirred for a further 3 h, diluted with pentane to precipitate nickel halide, and stirred for a further 4 h product (Y 82% E/Z 9 1). Subsequent treatment with acetals afforded 2-p-alkoxy-l,3-dioxolan-4-ones with asym. induction, thereby providing an alternative to asym. aldol condensation. F.e. inch reaction with ar. and a,P-ethylene-bromides s. D.J. Krysan, P.B. Mackenzie, J. Am. Chem. Soc. 110, 6273 (1988). 

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