Toward Understanding the Origin of Positive Effects of Ionic Liquids on Catalysis: Formation of More Reactive Catalysts and Stabilization of Reactive Intermediates and Transition States in Ionic Liquids

摘要

Over the past decade, ionic liquids have received a greatndeal of attention as a new means for catalyst immo-nbilization. Large numbers of catalysts having polar or ionicncharacter have been successfully immobilized in ionic liq-nuids, thus allowing their recovery and recycling. However,ncatalyst immobilization is not the only benefit of ionic liq-nuids in catalysis, of greater importance are the positive effectsnof ionic liquids on catalytic rates. In this Account, we high-nlight our work in elucidating the origin of the acceleratingneffects of ionic liquids in a range of catalytic reactions.nLewis acidic metal triflates often become much more reac-ntive in ionic liquids containing noncoordinating anions as anresult of “anion exchange.” Consequently, the more electro-nphilic Lewis acidic species generated in situ accelerate the cat-nalytic reactions dramatically. In some cases, highly reactivenintermediates, such as vinyl cations, arenium cations, oxy-ngen radical anions, and so forth, can be stabilized in the pres-nence of ionic liquids, thus increasing the reactivity andnselectivity of the reactions.