Synthesis of Pd(II) large dinuclear macrocyclic complex tethered through two dipyridine-bridged aza-crowns as an efficient copper- and phosphine-free Sonogashira catalytic reaction

Abstract

For the first time the new 32-membered macrocyclic dinuclear palladium complex of two aza-crown macrocycles, bearing two pyridine arms, Pd2L2Cl4 was synthesized and characterized by elemental analysis, IR, NMR spectroscopy and single crystal X-ray diffraction methods. Pd2L2Cl4 was investigated as a moisture/air-stable catalyst for Sonogashira cross-coupling reaction in the absence of copper and phosphine ligand in DMSO. Thermal stability, possible occurrence of tandem reactions, promoted catalytic performance as well as synergistic effects are of advantageous features of Pd2L2Cl4. By employing Taguchi method, optimum conditions (110 °C, 6 h, KOAc, 2 mol% cat.) were determined. Moreover, the homogenous catalyst represented good reusability up to four cycles. Comparing the catalytic activity of several other previously reported Pd(II) dinuclear complexes, Pd2L2Cl4 enjoys the advantages of short time of reaction and thermal stability.