Isolation of a C5-Deprotonated Imidazolium, a Crystalline “Abnormal” N-Heterocyclic Carbene

Abstract

Stretching Carbene Versatility: Stable N-heterocyclic carbene (NHC) molecules are versatile catalysts for organic reactions (see the Perspective by Albrecht ). Lavallo and Grubbs (p. 559 ) now show that these molecules can also catalyze organometallic transformations. Specifically, the carbenes induce coupling of monomeric iron olefin complexes to form clusters incorporating three or four bonded iron centers. Initial coordination of carbene to iron may facilitate formation of an iron-iron bond with a second complex. In a related development, Aldeco-Perez et al. (p. 556 ) prepared an NHC isomer in which the divalent carbon is shifted so that it no longer lies between the nitrogens. The compound forms stable complexes with both gold and CO ₂ .