Vinylcyclopropanes, complexes with iron

Iron carbonyl complexes are obtained by irradiation of iron pentacarbonyl with vinylcyclopropanes. The principal modes of reaction are (i) metal insertion into a strained bond with hydrogen migration to give diene-Fe(CO)3 complexes, (ii) metal carbonyl insertion to give a n-allyl-complexed acyl iron tricarbonyl, and (iii) cycloinsertion of CO across the homodiene to give a cyclohexenone. Similar types of... 

With the low-valence iron pentacarbonyl, vinylcyclopropanes 22 are thermally transformed to the diene re-complexes, the (1,3-trans-pentadiene)iron carbonyl complexes 23, through bond fission, 1,2-hydrogen shift, and stereoselective coordination [15]. (Scheme 9)... 

Whereas Fischer-type chromium carbenes react with alkenes, dienes, and alkynes to afford cyclopropanes, vinylcyclopropanes, and aromatic compounds, the iron Fischer-type carbene (47, e.g. R = Ph) reacts with alkenes and dienes to afford primarily coupled products (58) and (59) (Scheme 21). The mechanism proposed involves a [2 -F 2] cycloaddition of the alkene the carbene to form a metallacyclobutane see Metallacycle) (60). This intermediate undergoes jS-hydride elimination followed by reductive elimination to generate the coupled products. Carbenes (47) also react with alkynes under CO pressure (ca. 3.7 atm) to afford 6-ethoxy-o -pyrone complexes (61). The unstable metallacyclobutene (62) is produced by the reaction of (47) with 2-butyne in the absence of CO. Complex (62) decomposes to the pyrone complex (61). It has been suggested that the intermediate (62) is transformed into the vinylketene complex... 

The vinylcyclopropanes (87) interact with Fe(CO)5 to give the complexes (mechanism involving complex formation at the vinyl double bond followed by opening of the cyclopropane ring to give a 7r-allylic intermediate with an iron-carbon a bond has been mentioned (513). 

Alkyl-allyl complexes of isomeric systems can be interconverted and thus be used in isomerization of vinylcyclopropanes. Ethyl 4-azabicyclo[5.1.0]octa-2,5-diene-4-carboxylate (20) reacts with pentacarbonyliron to give complex 21, which photochemically rearranges to complex 23. Carbonylation of both products 21 and 23 leads to ethyl 9-oxo-2-aza-bicyclo[3.3.1]nona-3,7-diene-2-carboxylate (22). While complex 21 upon heating regenerates the starting material, complex 23 gives the isomeric product 24. In contrast to iron, with rhodium only the endo-complex 25 is formed. ... 

Conversion of monocyclic and polycyclic vinylcyclopropanes with low-valent transition-metal complexes, (e.g. iron, rhodium, zirconium, cobalt, nickel, palladium) mainly leads to ring opening and rearrangement products. A typical reaction pathway of vinylcyclopropanes with transition-metal complexes leads to f/Calkyl-j/ -allyl complexes, which as homodiene complexes exhibit interesting reaction patterns (e.g. carbonylation) leading to organic products. ... 

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