Treatment of the amino acid derivative Bz-His-OMe with excess n-propyl bromide gave the corresponding histidinium salt [Bz-His(n-propyl)2-OMe+Br-]. It features a melting point of 39 °C and may serve as a useful readily available optically active ionic liquid. Its subsequent treatment with silver oxide gave the corresponding l-histidine derived chiral N-heterocyclic carbene complex ["(carbene)2Ag • AgBr2"]. Transmetallation by treatment with Pd(CH3CN)2Cl2or [Rh(cod)Cl]2led to the formation of the respective chiral late metal imidazol-2-ylidene complexes ["(carbene)2PdCl2"] and ["(carbene)RhCl(cod)"], respectively. Four diastereomers of the square planar palladium system were observed. Due to the additional chirality center in the l-histidine-derived "Arduengo-carbene ligand" two diastereomers of the rhodium carbene complex were formed. © 2005 Elsevier B.V. All rights reserved.
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