An Alternative to Nitromethane as Solvent: The Promoting Influence of Nitro-Functionalized Imidazolium Salts for Synthesis and Catalysis

Nitromethane, a volatile and toxic organic compound, is commonly used as solvent for organic and catalytic reactions. In order to find an alternative for this specific nitro-containing organic solvent, the performance of some nitro-functionalized imidazolium salts such as 1-methyl-3-(4-nitrobenzyl)imidazolium hexafluorophosphate, 1-methyl-3-(4-nitrobenzyl)imidazolium tetrafluoroborate, 1-methyl-3-(4-nitrobenzyl)imidazolium bis(trifluoromethanesulfonyl)amide and 1,2-dimethyl-3-(4- nitrobenzyl)imidazolium hexafluorophosphate, was examined in some reactions including trimethylsilylation of alcohols with hexamethyldisilazane, ring-opening reactions of 2-aryl-3,4-dihydropyrans with thiophenols or thiols, and a copper- mediated oxidative coupling of alkynes. As expected, these imidazolium salts can indeed replace nitromethane in these reactions. Particularly, the imidazolium salt along with the metal catalyst, if involved, can be easily recovered and reused without significant loss of activity. The use of these nitro-functionalized imidazolium salts as alternative solvents for nitromethane not only confers a green aspect to the reaction system, but also facilitates a rational design of a catalytic system with the concept of green chemistry.