Palladium(ii) complexes bearing the 1,2,3-triazole based organosulfur/ selenium ligand: synthesis, structure and applications in Heck and Suzuki–Miyaura coupling as a catalyst via palladium nanoparticles

Air and moisture insensitive palladium complexes, [Pd(L)Cl2] (1/2), in which L = 1-benzyl-4-phenylthiomethyl or 1-benzyl-4-phenylselenomethyl-1H-1,2,3-triazole (L1 or L2) catalyze Heck (HC) and Suzuki–Miyaura coupling (SMC) reactions between a series of aryl bromides including deactivated bromides and n-butyl acrylate and phenylboronic acid, respectively. The optimal catalytic loading was found to be in the order of 0.01 mol%. HRTEM, TGA and EDX data indicated that 3–11 nm nanoparticles (NPs) composed of palladium and sulfur or selenium and protected with L or its fragment, were formed during the catalyzed reaction. The isolated NPs displayed catalytic activity and appeared to have a role in the catalysis. A two-phase test indicated that both homogeneous and heterogeneous catalysis took place. The complexes 1 and 2 were synthesized by the reactions of L1 and L2 respectively with [(MeCN)2PdCl2]. Their single crystal X-ray diffraction indicated that the geometry adopted by ligands around Pd in both complexes is distorted square planar with Pd–S and Pd–Se bond lengths of 2.2727(14) and 2.3693(8) A, respectively. DFT calculation gave bond lengths and angles in keeping with the experimental values. The DFT calculated HOMO–LUMO energy difference is lower for 1 than for 2 in accordance with the observed higher catalytic activity of 1.