Air-stable {(C5H5)Co} catalysts for [2+2+2] cycloadditions.

Cobalt cyclopentadienyl complexes incorporating a fumarate and a CO ligand (see picture) efficiently catalyze inter- and intramolecular [2+2+2] cycloadditions of alkynes, nitriles, and/or alkenes to give benzenes, pyridines, or 1,3-cyclohexadienes. Unlike catalysts such as [CpCo(CO)(2)] or [CpCo(C(2)H(4))(2)] (Cp = C(5)H(5)), they are air-stable, easy to handle, compatible with microwave conditions, and do not necessarily require irradiation to be active.