Structure-Activity Relationships of Glucose-based PdII-Bis(NHC) Complexes in a model Suzuki-Miyaura Reaction

The authors of this work have optimized a novel synthetic route towards glucose-based Pd(II)-bis(NHC) complexes in only 4 steps with total yields up to 73 %. The synthesis route encompasses an Appel reaction towards 6-iodo-glucopyranosides, followed by acyl-protection, then quaternization with imidazoles and finally the conversion of these acyl-protected glucosyl imidazolium salts to their respective palladium(II)bis(NHC) complexes, via an intermediary silver(I) complex. Overall, 11 acyl-protected glucosyl imidazolium iodides as NHC-precursors and 14 complexes have been synthesized. The structure-activity relationships of different functionalizations in these complexes and their reactivity in a model Suzuki-Miyaura between bromobenzene and 4-tolueneboronic acid reaction has been investigated, and a highly reactive complex leading to >99 % yield at 0.005 mol% catalytic loading has been found.