Synthesis, catalytic activity and medium fluorous recycle of fluorous analogues of PEPPSI catalysts

Abstract

PEPPSI complexes are air and moisture stable Pd catalysts, which can be used conveniently in many coupling reactions. With the aim to obtain Pd catalysts recyclable by fluorous separation methods, we modified the structure of commercial PEPPSI complexes by per- or polyfluoroalkylation in various positions. The modifications included the use of a linear polyfluoroalkyl group instead of one aryl group on the NHC ligand, perfluoroalkylation of pyridine ligand, and substitution of chloride ligands on Pd for perfluoroalkanoates or perfluoropolyoxaalkanoates. Comparison of catalytic activity of commercial catalysts with the modified ones in Suzuki-Miyaura cross-coupling reactions showed that the fluorous modifications mostly resulted in the increase of catalytic activity. Moreover, polyfluoroalkylation enabled efficient medium fluorous recycle of the modified catalysts using a two phase aqueous DMF/HFE 7500 ether system.