Electrochemical Synthesis of a Tetradentate Copper N-Heterocyclic Carbene Calix[4]arene and Its Transmetalation to Palladium: Activity of the Palladium Complex in Suzuki-Miyaura Cross-Coupling

A novel N-heterocyclic carbene 1,3-alternate calix[4]arene complex bearing four palladium(II) centers per ligand has been prepared. Electrochemical synthetic methods were used to prepare the corresponding copper(I) complex, followed by transmetalation onto palladium(II). The activity of the palladium complex was probed in the Suzuki-Miyaura cross-coupling reaction. An inverse correlation between palladium concentration and activity was observed, with the results indicating that calix[4]arenes in the cone conformation may reduce the aggregation of palladium(0) nanoclusters, whereas our 1,3-alternate calix[4]arene does not provide any supramolecular stabilizing effect.