The phase diagram and microstructure of the ternary system ionic, liquid benzylpyridinium bis(trifluoromethanesulfonyl)imide)/nonionic surfactant (octylphenol ethoxylate)/toluene, were studied by using conductivity measurements, dynamic light scattering, pulse field gradient spin-echo NMR, and small-angle neutron scattering. Three microregions were identified by conductivity measurements according to the percolation theory. The sizes of IL-in-oil microemulsions with various IL fractions were then determined by NMR and DLS and were found to be in accordance with the radii of gyration (approximately 2 or 3 nm) determined by SANS. The reverse IL-in-oil microemulsions were used as nanoreactors to perform a Matsuda-Heck reaction between p-methoxyphenyl diazonium salt and 2,3-dihydrofurane in the presence of a palladium catalyst. The reaction yields obtained were greater in microemulsions (67%) than in bulk IL (33%), highlighting a strong effect of confinement. Moreover, a direct correlation between the quantity of IL and the reaction yield was observed.