Suzuki-cross-coupling reactions catalyzed by a new water dispersible Pd-NHC catalyst

Transition-metal-catalyzed cross-coupling reactions have become a routine, straightforward, and powerful method for the preparation of carbon–carbon and carbon–heteroatom bonds in synthetic organic chemistry [1, 2]. Recently, N-heterocyclic carbene (NHC) ligands and their metal complexes have attracted many attentions in transition metal catalysis due to their ease of preparation, the strong σ-donor ability and effective binding strength to transition metals. The NHC transition metal complexes have been extensively used in organic transformations especially coupling reactions including Heck, Kumada and Suzuki– Miyaura. Immobilization of homogeneous catalysts on the magnetic nanoparticles (MNPs) produces heterogeneous catalysts which can be easily isolated by using an external magnet. However, in most cases, the efficiency and selectivity of heterogeneous catalysts supported on MNPs are not desirable in water as a green solvent. To conquer this problem, micelles, surfactants or organic co-solvents have been used. A more desirable approach, which avoids using any additives, is designing water-dispersible MNPs. This allows reactions to be performed in pure water under near homogeneous conditions and also allows catalyst separation from the reaction mixture simply by an external magnetic field [3, 4]. In the work, we have synthesized a novel water-dispersible/magnetically recyclable Pd-NHC catalyst. The synthesized catalyst was characterized by FT-IR, XRD, XPS, EDX, TGA, VSM, TEM, and FE-SEM. We have successfully used this catalyst as a water-dispersible/magnetically recyclable Pd heterogeneous catalyst for Suzuki-cross-coupling reactions in neat water.