Study of the reactivity of ClCo(PPh3)3

The catalytic activity of ClCo(PPh₃)₃ in oligomerization of alkynes and reduction of carbonyl compounds has been investigated. Monosubstituted alkynes with an electron withdrawing group give quantitative yields of arene derivatives when reacted with 5 mol% of ClCo(PPh₃)₃. Cyclotrimerization of disubstituted alkynes with at least one electron withdrawing group requires the addition of NaBPh₄. In the oligomerization of phenylacetylene, cyclotrimerization and linear dimerization are in competition. However, when the reaction is run in the presence of 1.2 equiv. of NaOMe at room temperature, only linear dimerization is observed. Diethyl allylpropargylmalonate also cyclodimerizes or codimerizes with diphenylacetylene by catalytic amount of ClCo(PPh₃)₃ in the presence of NaOEt. Reaction of a variety of carbonyl compounds with 5 mol% of ClCo(PPh₃)₃ in i-propanol leads to the reduction of the compounds to the corresponding alcohols. The reaction requires the addition of NaH which produces (i-PrO)Na in situ. The role of alkoxides or NaBPh₄ in ClCo(PPh₃)₃ catalyzed oligomerization of alkynes or reduction of carbonyl compounds is discussed.