Iron complexes, with cyclo-octatetraene

Treatment of iron carbonyls with cyclo-octatetraene forms complexes such as CsH8Fe(CO)3, CsHsFezCCO), and C8H8(Fe(CO)3)2 [26,27,28,28a, 29]. The structures of these complexes have been determined by X-ray studies and are 6.7, 6.8 and 6.9 respectively. In the complexes 6.8 and 6.9 the... 

Irradiation of solutions of cycloheptatrieneiron tricarbonyl at low temperatures followed by addition of diphenylacetylene produces the [2 + 6] adduct, 7,8-diphenyl-bicyclo[4,2,l]octa-2,4,7-triene similar results were obtained with cyclo-octatetraene-iron tricarbonyl and related compounds. The mechanism suggested involved photo-induced replacement of one of the olefin bonds or carbon monoxide ligands in the complexes by a solvent molecule, thermal replacement of the solvent by the acetylene, and an intramolecular cycloaddition. ... 

Cyclo-octatetraene reacts with iron carbonyls to form complexes with the compositions [Fe(CO)3(C8H8)], [Fe2(CO)6(C8H8)], and [Fe2(CO)7(C8H8)] 152, 168, 180). Nakamura and Hagihara 166) report that the complex [Fe(CO)3(C8H8)] decolorizes bromine in carbon tetrachloride and shows absorption bands in its infrared spectrum at 699, 716, and 720 cm-1 due to cis-double bonds. They suggest structure (XVI) for this complex, i.e., the hydrocarbon retains its tub form in the complex. These results are con-... 

A single crystal X-ray structural determination of the binuclear complex [Fe2(CO)6(C8H8)] (64a) shows it to have the structure (XVIII) and not one of the previously suggested structures 22, 54,152,166,174) including tub and planar forms of the cyclo-octatetraene ring. The cyclo-octatetraene ring in the complex approximates to a chair form in which the four carbon atoms associated with each iron atom are planar or very nearly so. The observed Fe—C and C—C distances in this complex are compared... 

Cycloaddition.— Reactions of electrophilic olefins and acetylenes with tricarbonyl-iron complexes of cycloheptatriene and cyclo-octatetraene lead to 1,3-exo-products. Troponetricarbonyliron and tcne, however, have now been found to give complex (20) which results from previously unobserved 1,5-exo-cycloaddition. A dipolar intermediate (21) resulting from initial attack by the electrophile on the hydrocarbon... 

Me, = H 71 %) and (208 R = H, R = Me 21.5 %) was obtained from the iron tricarbonyl complex of methylcyclo-octatetraene. Oxidation of these adducts with ceric (iv) ion gives dihydrotetracyanotriquinacenes in good yield. tcne reacts with the iron-tricarbonyl complex of unsubstituted cyclo-octatetraene to give the 1,3-adduct (208 R = R = H) which is oxidized by cerium (iv) to a dihydrotetracyano-triquinacene. ... 

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