Formation of chiral ionic liquids and imidazol-2-ylidene metal complexes from the proteinogenic aminoacid L-histidine

Treatment of the amino acid derivative Bz-His-OMe with excess n-propyl bromide gave the corresponding histidinium salt [Bz-His(npropyl)(2)-OMe+Br-]. It features a melting point of 39 degrees 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)(2)Ag (.) AgBr2]. Transmetallation by treatment with Pd(CH3CN)(2)Cl-2 or [Rh(cod)Cl]2 led to the formation of the respective chiral late metal imidazol-2-ylidene complexes [(carbene)(2)PdCl2] 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. (c) 2005 Elsevier B.V. All rights reserved.