Green Synthesis of Alkane Bridged Bisimidazolium Salts Under Solvent-Free Conditions

Abstract

A series of N-aryl or N-methyl substituted bisimidazolium dichloride or dibromide salts with different alkyl bridge lengths (n = 1–4) have been synthesized starting from N-arylimidazoles or N-methylimidazoles with dialkyl bromides or the less expensive but less reactive dialkyl chlorides under solvent-free conditions. This green protocol provided most bisimidazolium chloride and bromide salts in good yields, and the reaction time was shortened to a few hours. In two examples, we showed either bisimidazolium dichloride (1a) or dibromide salt (3c) can be easily converted to the corresponding dihexafluorophosphate salt (1a′ or 3c′) in near quantitative yield.

GRAPHICAL ABSTRACT

Keywords:

• Bisimidazolium salts
• N-arylimidazoles
• N-heterocyclic carbenes
• N-methylimidazoles
• solvent-free

ACKNOWLEDGMENTS

We are grateful to SRF for ROCS, SEM, PAPD; State Key Laboratory of Inorganic Synthesis and Preparative Chemistry (2009-06) at Jilin University; Qing Lan Project (08QLT001 and 08QLD006) of Jiangsu Education Committee; and the National Natural Science Foundation of China (21071121, 21172188, and 21104064) for financial support.