Octacarbonyldicobalt complexes Pauson-Khand reaction

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). ... 

This review has already indicated numerous applications of dicobalt-alkyne complexes in organic synthesis. Like the Nicholas reaction (see Section II,D), the Pauson-Khand reaction has seen widespread use.175 This reaction is a three-component cycloaddition of alkynes with alkenes and carbon monoxide which occurs in the presence of octacarbonyldicobalt to afford cyclopentenones, as shown in Eq. (16). 

The alkyne-Co2(CO)6 complexes 1 are the binuclear cluster complexes of the acetylenic derivatives with the hexacarbonyldicobalt moiety. These complexes can be readily prepared by treatment of alkynes with commercially available octacarbonyldicobalt [Co2(CO)g] and can regenerate the parent triple bond functionality under some mild oxidation conditions. Two synthetically very useful reactions have so far been developed by taking advantage of the characteristic properties of the alkyne-Co2(CO)6 complexes 1 one is so-called Nicholas reaction" and the other is so-called Pauson-Khand reaction (Scheme 1). The alkyne-Co2(CO)6 complexes 1 possessing a hydroxyl group or its equivalent at carbon p- to alkyne moiety (propargyl alcohol derivatives) could easily... 

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