Efficient activation of 2-Iminomethylpyridine/Cobalt-Based alkyne [2+2+2}cycloaddition catalyst by addition of a silver salt

The addition of silver triflate (AgOTf) or silver hexafluoroantimonate (AgSbF6) significantly increased the activity of the 2-(arylimino)methyl-pyridine/cobalt(II) chloride hexahydrate (COCl2 center dot 6H(2)O)/zinc catalyst in alkyne cyclotrimerizations thereby accelerating the reaction and enabling the use of unactivated, simple internal alkynes as the monoyne substrate: The rate of reaction was found to be highly dependent on the nature of the counter anion (X-) and the ligand (L) in the postulated cationic cobalt(I) complex [LCo(l)]X-+(-).