Cobalt, complexes benzene

Upon treatment with suitable cobalt complexes, methylbutynol cyclizes to a 1,2,4-substituted benzene. Nickel complexes give the 1,3,5-isomer (196), sometimes accompanied by linear polymer (25) or a mixture of tetrasubstituted cyclooctatetraenes (26). 

Only a few other cobalt complexes of the type covered in this review (and therefore excluding, for example, the cobalt carbonyls) have been reported to act as catalysts for homogeneous hydrogenation. The complex Co(DMG)2 will catalyze the hydrogenation of benzil (PhCOCOPh) to benzoin (PhCHOHCOPh). When this reaction is carried out in the presence of quinine, the product shows optical activity. The degree of optical purity varies with the nature of the solvent and reaches a maximum of 61.5% in benzene. It was concluded that asymmetric synthesis occurred via the formation of an organocobalt complex in which quinine was coordinated in the trans position (133). Both Co(DMG)2 and cobalamin-cobalt(II) in methanol will catalyze the following reductive methylations ... 

Organocobalt complexes catalyze the cyelocotrimerization of acetylenes and nitriles, which affords pyridine and benzene derivatives (100). (Cyclo-pentadienyl)cobalt complexes such as CoCp(COD) favor pyridine formation (100), and modification of the Cp ligand has considerable influence on the activity of the catalyst and the chemo- and regioselectivity of the catalytic process (101). 

Courtot-Coupez and Le Bihan [209,210] determined the optimum pH (7.4) for extraction of non-ionic surfactants with the above complex-benzene system. Cobalt in the extract is estimated by AAS after evaporation to dryness and dissolution of the residue in methyl isobutyl ketone. The method is applicable to surfactant concentrations in the range 0.02-0.5 mg/1 and is not seriously affected by the presence of anionic surfactants. 

C7H4N, Benzonitrile platinum complex, 26 345 ruthenium (II) complexes, 26 70-72 CiH , Benzene, methyl-cobalt complex, 26 309 manganese complex, 26 172... 

C18H18, Benzene, l,3-butadiene-l,4-diyl-bis-cobalt complex, 26 195 C,8H33P, Phosphine, tricyclohexyl iron complex, 26 61 nickel complexes, 26 205, 206 C H 7OP, Benzenemethanol, 2-(diphenyl-phosphino)-... 

There are now two possible routes to the final product. Reductive elimination would insert the new alkyne into one of the old C-Co bonds and form a seven-membered ring heterocycle. This could close in an electrocyclic reaction to give the new six-membered ring with the cobalt fused on one side and hence the cobalt complex of the new benzene. 

In the presence of suitable nickel or cobalt complexes, propargyl alcohol trimerizes to a mixture of 1,3,5-benzenetrknetlianol [4464-18-0] and 1,2,4-trimethanol [25147-76-6] benzene (28). 

Figure 11 Structure of benzene(butyne)cobalt complex...

F4OW, Tungsten fluoride oxide, 24 37 F4SE, Selenium tetrafluoride, 24 28 FsCJH, Benzene, pentafluoro-cobalt complexes, 23 23-25 lithium and thallium complexes, 21 71,... 

C H,a, Benzene, 1,3-butadiene-1,4-diyl-bis-, cobalt complex, 26 195 CjaHjaBr, Benzene, l-bromo-2,4,6-tri-tert-butyl-, 27 236... 

Binuclear complexes of naphthalene (VIII) and of benzene (IX) with [Os(NH3)5]2+ and [Ru(NH3)5]2+ moieties were reported by Taube et al. (19), in which anti- //-1,2-rj2 3,4- 2) coordination of the arene is present. This bonding mode was first observed by Pasman et al. (20) in the binuclear Rhenium complex X. Wolczanski et al. (21) obtained complex XI from the mononuclear complex [Ta(0—Si Bu3)3 2-(N,C)-pyridine ] and benzene. Each tantalum atom is bound unsymmetrically to one C=C bond of benzene with a weak interaction to a third carbon atom the bonding may be described as a distorted tj3-enyl. In the dinuclear cobalt complex XII, the xylene functions as a bis(enyl)-ligand (12,22). 

Another type of activation of aluminum alkyl was found in the asymmetric-selective polymerization of epichlorohydrin (ECH) with an optically active cobalt-salen type complex [Co (II)]. The structure of the salen-type cobalt complex was shown previously (13, 14). In a benzene solution of the binary system consisting of [Co (II)] and AlEt, no evolution of ethane or ethylene was observed at room temperature. The NMR signals of the methyl protons for AlEt shifted down field on mixing with [Co (II)]. These observations together with a circular dichroism study indicated that AlEt and [Co (II)] formed a molecular complex in benzene, none of Al-Et bonds being cleaved by this complexation. 

Borohydride and alkyllithium reagents engage in nucleophilic addition to -benzene or f -hexamethylbenzene ligands in various cationic third-row transition-metal complexes, producing neutral )y -cyclohexadienide products " . Similarly, the cobalt complex XXXVIII adds hydride and n-butyllithium to give the -cyclo-butadienyl- j -cyclo-hexadienyl-Co complex XXXIX in moderate yield ... 

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