Intermediate, Iron-dienyl

There is recent kinetic evidence from the solvolysis rates of iron tricarbonyl dienyls that rom-7r-pentadienyl species are reaction intermediates (45). There are two structures proposed, as shown ... 

Dehydration of (2-hydroxymethyl-1,3-butadiene)iron complexes or (hydroxymethyltrimethylenemethane)iron complexes with fluorosulfonic acid/liquid sulfur dioxide generates the corresponding (cross-conjugated dienyljiron cations (194) (equation 72). The H and NMR spectral data for these cations favor an " -TMM-methyl cationic structure (282) over an ) " -isoprenyl cationic stmcture (283). These cations react with water or alcohols to afford butadiene products via nucleophilic attack at C-5. As indicated earlier (Section 6.1.1), the cross-conjugated dienyl cations are believed to be intermediates in the substitution of (193) with weak carbon nucleophiles (Scheme 53). In these cases, nucleophihc attack occurs on C-4 to give predominantly TMM products. ... 

A similar type of reaction has been observed in the reactions of iron-caibene complexes with 1,3-dienes. In this case the direction of reductive elimination in the metal hydride intermediate corresponding to (193) is constrained to that which generates a conjugated 1,3-diene however, two isomeric products are also obtained from this reaction which are epimers about the face of the diene to which the iron tricarbonyl group is attached. This reaction produces highly functionalized 1,3-dienyl complexes of iron in high yield under relatively mild conditions and will likely play a role in the development of the... 

At room temperature, this adduct readily decomposes by homolytic cleavage to the 19-electron-17-electron radical pair which subsequently forms homodimers of the iron and the molybdenum complexes similar to those in Eq. 51. An overall electron transfer via the nucleophilic adduct as intermediate is observed as the favored pathway of iron complexes with acyclic dienyl ligands. However, the formation of the electron-transfer products, viz., homodimers of iron and molybdenum complexes, are also obtained directly (in 25 % yield) during the reaction. The nucleophilic adduct is not a prerequisite for the electron transfer from the molybdate... 

Table 2 summarizes the mixed arene-arene and arene-ligand complexes prepared. w-Arene complexes of polymers are also listed. Iron and Ru with benzene or toluene yield t-arene complexes that can be isolated at low temperature. The (CgHg)2Ru species is stable to 0°C, whereas the CgHjCHj-Fe analog is stable to — 50°C. Thus, these compounds can be isolated for use as intermediates in other reactions, e.g., the addition of cyclopentadiene to the (benzene) Fe complex, where on warming hydrogen transfers to benzene to yield ( -cyclopentadienyl) ( -cyclohexa-dienyl)Fe ... 

Other Enzymes Insufficient is still known about other enzymes that may also operate via M—C bonds. Lipoxgenases convert polyunsaturated fatty acids, such as arachidonic acid, to hydroperoxides. These can go on to form prostaglandins, which are known to regulate a variety of processes, such as inflammation. Corey has proposed that certain lipoxygenases deprotonate one of the central protons in a segment of arachidonic acid to give a penta-dienyl iron intermediate that reacts with O2 to give the hydroperoxide product. 

Reaction of l-chloro-l-(phenylthio)alkanes with sodium dicarbonyl(cyclopenta-dienyl)ferrate provides (a-phenylthio)alkyliron complexes. If these complexes have a double bond in their side chain in an appropriate distance to the iron center, methylation of the thioether results in an intramolecular cyclopropanation via the corresponding sulfonium salt and the (alkylidene)iron complex as intermediates (Scheme 4—63). ... 

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