Nitrile-functionalized pyrrolidinium-based ionic liqs. were prepd. and characterized by spectroscopic methods and x-ray crystallog. The application of these new ionic liqs. as reaction media for Suzuki and Stille C-C cross-coupling reactions was studied and compared with related imidazolium and pyridinium systems (including those with and without nitrile functionalities). The nature of the ionic liq. strongly influences the catalyzed reaction and it would appear that, in addn. to the nitrile group, the strength of anion-cation pairing in the ionic liq. and the viscosity of the ionic liq. play crit. roles. Nanoparticles are also detected following catalysis and their role, and the influence of the ionic liq. on them, is assessed. The ability to use the nitrile-functionalized pyrrolidinium-based ionic liqs. dild. in other (nonfunctionalized) ionic liqs. is also described.