Sugar-coated carbene

As organic catalysts and as ligands in transition-metal complexes, N-heterocyclic carbenes (NHCs) are growing in popularity. In the latest twist in their development, Takanori Nishioka, Teppei Shibata, and Isamu Kinoshita of Osaka City University, in Japan, have synthesized the first reported example of an NHC complex (shown) containing a saccharide group as a substituent (Organometallics 2007, 26, 1126). Incorporating saccharide groups into transition-metal complexes improves their solubility in water and their molecular recognition properties, which are useful in ion sensing, catalysis, and drug delivery, the researchers note. To make the new ligand, they added a glucopyranosyl group to 1-methylimidazole, reacted the intermediate with silver(I) oxide to form a silver NHC complex, and transferred the ligand from silver to iridium in a final step. The Osaka researchers now are using this strategy to prepare complexes with multidentate saccharide-substituted NHC ligands and with different metals, Nishioka says.