Efficient palladium-catalyzed Heck reactions mediated by the diol-functionalized imidazolium ionic liquids

The diol-functionalized imidazolium ionic liquids, 1-(2,3-dihydroxypropyl)-3-methylimidazolium hexafluorophosphate (1) and 2,2-bis(1-methyl-methylimidazolium) propane-1,3-diol hexafluorophosphate (2), were synthesized and used as the phosphine-free ligands in the palladium-catalyzed Heck reaction of aryl bromides with electron-deficient olefins. Under aerobic conditions, the efficient arylation of acrylates could be accomplished when catalyzed by PdCl2-2 (or 1) in DMF with Et3N as a base, in terms of good activities, excellent selectivities (to trans-coupling products), and reusability, due to the available multiple coordinating sites like bidentate diol and NHC carbene in the ligands.