Triene-iron carbonyl complexes

Ci6Hi2Fe206f Bicyclo[6 2.0]deca-2,4,6 triene iron carbonyl complex, 39B, 641... 

Only two instances of attempts to make acyclic triene-iron carbonyl complexes have been reported. Alloocimene (XL) forms an Fe(CO)3 complex when treated with Fc3(CO) 12 (.5. Inviewof the possibility of rearrangement having occurred the structure of this material remains questionable. 

A diene system with unsymmetrical 1,4-disubstitution is converted to the iron carbonyl complex 1 which is resolved into its enantiomers. The aldehyde function is conformationally locked in the transoid position and is diastereofacially shielded from the bottom face. Nucleophiles attack from the top face with high selectivity. Alternatively, chain elongation leads to the triene 2 which is reacted with diazomethane. Cerium(IV) oxidation removes the metal and furnishes the substituted cyclopropane 3. 

The mass spectra of some binuclear iron carbonyl complexes of the type (triene) Fe2(CO)g have been investigated 26>33b Reaction between... 

Tricarbonyliron complexes of conjugated trienes react with diazoalkanes at the free (uncom-plexed) double bond. In the synthesis of dimethyl 2-formylcyclopropane-l, 1-dicarboxylate (48), the ceric ion served the double function of catalyzing the deazetization and removing the tricarbonyl iron protecting group. When the optically active iron carbonyl complex was used, the addition of diazomethane gave selectively one diastereomer and this was used to make optically active dimethyl 2-formylcyclopropane-l,1-dicarboxylate (>90% ee). A similar route was employed to make the optically active formyl cyclopropanes 49, precursors to optically active cis- and tran.v-chrysanthemic acids. 

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. ... 

Another triene system which has been briefly studied is 8,9-dihydroindene (XXXIX) (65). With iron carbonyl this material affords an iron-tricarbonyl complex, the instability of which, it has been suggested, indicates two non-conjugated double bonds are involved in the bonding to Fe. 

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