Iron complexes cyclo-octatetraene

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... 

The compound cyclopentadienylcyclo-octatetraenecobalt is probably analogous to the compound cyclopentadienyl cyclopentadienecobalt (XXIV). The cyclo-octatetraene residue shows two proton resonance lines in the nmr spectrum (167) in contrast to that in the iron complex [Fe(CO)3(cyclo-octatetraene)] which shows only one proton resonance line (152, 180). 

Isomerization of safrole and eugenol is reported to occur when these alkenes are irradiated in the presence of iron carbonyls. Co-ordinatively unsaturated iron carbonyls are first formed and subsequently give iron carbonyl-alkene complexes whose alkene ligands are then isomerized. A further reported photoinduced isomerization involves Fe(fnb-Ti -cot)(CO)3 (cot = cyclo-octatetraene), which on irradiation in a CH4 matrix at 12 K is converted into Fe(cfiair-Ti -cot)(CO)3 via Fe(T -cot)(CO)3 as intermediate. The results of these studies are related to the fluxional behaviour of Fe(i7 -cot)(CO)3 in solution. ... 

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. ... 

The bicyclo[4,2,0]octa-2,4,7-trienyl iron carbonyl complexes (285) and (286) are stable, even in refluxing benzene, in marked contrast to the rapid valence isomerization of free bicyclo[4,2,0]octa-2,4,7-triene to cyclo-octatetraene. This stability is due to the loss of the inert gas configuration on rearrangement to a diTiapto-cyclo-octatetra-ene-Fe(CO)3 complex. The inert gas structure could be retained if the cyclobutene ring of the complexes opened via a forbidden disrotatory opening, but this does not occur because the metal is not in a position to help sterically. ... 

A useful method for the release of organic ligands from iron complexes has been developed using trimethylamine oxide. It is suitable for releasing ligands which are easily oxidized and which cannot be released by the more conventional oxidizing agents examples include the release of tropone and cyclo-octatetraene from their iron carbonyl complexes. ... 

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... 

Cyclo-octatetraene and SO2 reacted in the presence of SbFj to give a mixture of (206 X = SO2) and the 1,4-adduct (205 X = SO2) (206) may have been formed by collapse of the zwitterion (207). Addition of tcne to several iron tricarbonyl complexes of monosubstituted cyclo-octatetraenes (Me, Ph, MeO, COjMe, benzo, substituent) occurs via 1,3-bonding to give ri" -products, e.g. a mixture of (208 =... 

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. ... 

There is wide-line n.m.r. evidence for fluxional behaviour even in the solid state, as, for example, for the cyclo-octatetraene complex (18) and the di-iron species Fe2(C8H8)(CO)6. ... 

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... 

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