Pentacarbonyliron reactions with alkynes

Yellow complexes of formula RC2R Fe(CO) have been obtained from Me CCesCCMe, Me SiCsCSiMe and PhCsCSiMe, and are regarded as alkyne substituted, pentacarbonyliron compounds for which a structure analogous to acrylonitrile Fe(CO) (4) has been adopted. Their further reaction with other alkynes at room temperature leads to complexes of types (RC Rj COFe CCO), (RC Rl Fe fCO), and (RC2R) Fe2(CO)g and is discussed together with their role in the formation of quinones. 

A formal [2+1+1] cycloaddition is achieved by reaction of alkynes with an iron carbonyl species that is prepared in situ from dodecacarbonyltriiron Fe3(CO)i2 in the presence of certain amines. This procedure provides cyclobutenediones in moderate to good yields after demetalation with copper(II) chloride (Scheme 4-14). Instead of amines and dodecacarbonyltriiron, alkoxides such as ter/-BuOK can be reacted with pentacarbonyliron to give reactive carbonyliron intermediates that undergo cyclization... 

In an analogy to the well-known octacarbonyldicobalt-mediated Pauson-Khand reaction, the formal [2+2+1] cycloaddition of alkyne, alkene, and carbon monoxide can be promoted by pentacarbonyliron. However, the iron-mediated [2+2+1] cycloaddition of two alkynes with carbon monoxide has attracted much more attention. When heated in glyme at 140 °C in the presence of stoichiometric amounts of penta-carbonyliron, substituted trimethylsilylacetylenes afford tricarbonyliron complexed cyclopentadienones in moderate to good yields (Scheme 4-3). ... 

Cyclization of an alkyne to an alkene with carbonyl insertion (analogous to the Pauson-Khand reaction) has also been achieved using pentacarbonyliron. ... 

---