N-Alkoxyimidazolylidene Transition-Metal Complexes: Application to [5+2] and [4+2] Cycloaddition Reactions

Silver(I) bis[(benzyloxy)imidazol-2-ylidene] complex 6 is prepared by reaction of an alkoxyimidazolium bromide (4) with Ag2O. In situ deprotonation of the alkoxyimidazolium bromide 4 afforded the rhodium(I) and palladium(II) complexes 7 and 8, whose structures were verified by X-ray crystallography. Rhodium(I) (benzyloxy)imidazolylidene complex 7 efficiently catalyzes the [5+2] cycloaddition reaction of an yne−vinylcyclopropane (93%) and the [4+2] cycloaddition reaction of a diene−yne (99%) at room temperature in minutes.