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Benzenimidazole-Functionalized Imidazolium-Based N-Heterocyclic Carbene Complexes of Silver(I) and Palladium(II): Isolation of a Ag3 Intermediate toward a Facile Transmetalation and Suzuki Coupling

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posted on 25.02.2008, 00:00 by Fuwei Li, Shiqiang Bai, T. S. Andy Hor
A new benzenimidazole-functionalized imidazolium-based N-heterocyclic carbene complex of Pd(II) has been prepared from facile transmetalation via a Ag(I) precursor. The latter was obtained from a condensation reaction between Ag2O and benzenimidazolium salt. Single-crystal X-ray crystallography revealed an unusual trinuclear Ag3Cl2(μ-Cl)(μ-N-C)2 (N-C = 3-methyl-1-(1-ethyl-2-methylbenzoyl)imidazolin-2-ylidene) intermediate in which the central carbene-supported Ag(I) is flanked by two imidazole-coordinated Ag(I). The hybrid ligand (N-C), carrying two heterodonors of benzenimidazole and carbene, is bridging in Ag(I) but chelating in Pd(II). The latter mononuclear PdCl2(η-N-C) is active toward Suzuki−Miyaura coupling of aryl bromides and boronic acids, giving a TON up to 11 750 within 4 h at rt.