Activation of alkyne-dicobalt hexacarbonyl complexes by the Lewis bases - A new trend in the Pauson-Khand reaction

Abstract

Cyclic cotrimerization of an alkyne, an alkene, and carbon monoxide mediated by dicobalt octacarbonyl, which is well known as the Pauson-Khand reaction, was promoted by the addition of certain Lewis bases. Primary amines with secondary alkyl groups, such as cyclohexylamine, promoted the stoichiometric Pauson-Khand reaction to give the desired cyclopentenones in good yields. The same reaction can be conveniently carried out in 1,4-dioxane-aqueous NH4OH biphasic system. Some reactive cobalt complexes might be produced as the coproduct in the reaction mixture and decomposed the substrate and/or the product in some cases. To overcome this disadvantage, alkyl methyl sulfides were introduced as the promoter. The catalytic Pauson-Khand reaction was also promoted by the addition of a tiny amount of DME or water. A novel decomplexation method of alkyne-dicobalt hexacarbonyl complexes by using ethylenediamine and a hydrocarbamoylation reaction were also presented.