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 fororganic and catalytic reactions. In order to find an alternative for this specificnitro-containing organic solvent, some nitro-functionalized imidazolium salts such as1-methyl-3-(4-nitrobenzyl)imidazolium hexafluorophosphate,1-methyl-3-(4-nitrobenzyl)imidazolium tetrafluoroborate,1-methyl-3-4-(nitrobenzyl)-imidazolium bis(trifluoromethanesulfonyl)amide and1,2-dimethyl-3-(4-nitrobenzyl)imidazolium hexafluorophosphate were synthesized.The following three kinds of reactions of nitro-containing functionalized imidazoliumsalts as catalysts, solvents or the performance of the additives are examined in this paper,including trimethylsilylation of alcohols with hexamethyldisilazane, ring-opening reactionof2-aryl-3,4-dihydropyrans with thiophenols or thiols, and a copper-mediated oxidativecoupling of alkynes. All of the three reactions have obtained good yields.As expected, these imidazolium salts can indeed replace nitromethane in thesereactions. Particularly, the imidazolium salt along with the metal catalyst, if involved, canbe easily recovered and reused without significant loss of activity. The use of thesenitro-functionalized imidazolium salts as alternative solvents for nitromethane not onlyconfers a green aspect to the reaction system, but also facilitates a rational design of acatalytic system with the concept of geen chemistry.