Rhodium N-Heterocyclic Carbene Complexes as Effective Catalysts for [2+2+2]-Cycloaddition Reactions.

Rhodium complexes of N-heterocyclic carbenes (NHC) [RhCl(cod)(NHC)], [cod = 1,5-cyclooctadiene, NHC = 1,3-diisopropylimidazolin-2-ylidene, and NHC = 1,3-dimesitylimidazolin-2-ylidene] are tested for intra- and partially intramolecular [2+2+2]-cycloaddition reactions demonstrating their effectiveness in this kind of process. This is the first use of a rhodium-NHC complex in a [2+2+2]-cycloaddition reaction of three alkynes. ESI-MS has been used to detect oxidative addition intermediates using rhodium NHC as the catalytic system. [ABSTRACT FROM AUTHOR]