Recent developments in amino acid-derived imidazole-, imidazolium- and N-heterocyclic carbene-carboxylate complexes

Abstract

Compounds based on imidazole or imidazolium moieties are excellent building blocks for the preparation of a plethora of ligand precursors. The introduction of chirality in these compounds is relatively easy through the Debus-Radziszewski reaction, in which the chiral pools are natural or non-natural amino acids. Using this synthetic route, enantiopure imidazole-carboxylate, imidazolium-carboxylate, and imidazolium-dicarboxylate ligand precursors can be prepared, from which N-heterocyclic carbenes (NHC) with one or two carboxylate groups can also be obtained. This review is a personal account that summarizes our recent results regarding the use of all these compounds as chiral ligands coordinated to several transition metals (Cu, Zn, Ag and Mo). The structural features of the new synthesized coordination polymers with novel bonding modes will be described, and the bonding capabilities of these ligands rationalized on the basis of theoretical calculations. The efficiency of homochiral imidazolium-dicarboxylate compounds as chiral inductors in asymmetric catalysis will also be discussed. Finally, the antimicrobial and antitumoral activities of imidazolium- and NHC-carboxylate silver complexes and the found chirality-activity and structure–activity relationships will be highlighted.