Expedient Synthesis of Bis(imidazolium) Dichloride Salts and Bis(NHC) Complexes from Imidazoles using DMSO as a Key Polar Additive

Abstract

A general approach for the synthesis of bis(imidazolium) dichloride salts from imidazoles and dichloroalkanes is reported. Typical limitations of this reaction for the formation of methylene-bridged derivatives are addressed herein through the use of an excess CH2Cl2 in the presence of DMSO as a polar cosolvent, significantly improving conversion rates presumably via stabilization of the initial SN2 transition state. The method was also shown to be applicable to the formation of bis(pyridinium) dichloride salts from pyridine derivatives, and to the direct synthesis of metal-bis(NHC) complexes from imidazoles.

N-Heterocyclic Carbene Ligands’ Electronic Effects on Metallopolymer Anion Exchange Membranes

“…25 Additional studies have showed that multidentate bis-or tetrakisimidazolium salts can lead to the formation of [NHC 2 − AuCl 2 ]Cl and [NHC 4 −AuCl 2 ]Cl complexes using similar reaction conditions. 30,31 Consequently, due to the high NHC ligand local concentration in the polymer precursors, such oligo-NHC Au complexes could be obtained and need to be considered as well. Accordingly, before proceeding with any type of AEM tests, it is necessary to ascertain the type of complexes obtained within each of the metallopolymers.…”