Synthesis and characterization of bidentate NHC–Pd complexes and their role in amination reactions

The new well-defined and air-stable ortho-xylyl-linked N-heterocyclic carbene (NHC) Pd complexes (2a–d) have been synthesized and characterized by elemental analysis, 1H NMR, 13C NMR, IR spectroscopy, and single crystal X-ray diffraction studies. The palladium atom in the complex 2a lies on a crystallographic mirror plane and can be described as having a square-planar coordination environment with the carbene atoms of the benzimidazole rings of the ligand occupying two coordination sites in cis positions. Two further coordination sites are occupied by chloride ligands. The benzimidazole rings are connected to each other by an ortho-xylyl bridge. The catalytic activity of these palladium complexes has been tested in the coupling reactions of various N-containing substrates with bromobenzene. A preliminary catalytic study shows that the bis(NHC)–Pd complexes are highly active in the Buchwald–Hartwig amination reaction.

Graphical abstractThe synthesis of new well-defined and air-stable ortho-xylyl-linked(NHC)–Pd complexes is described, and the complexes are characterized by spectroscopic techniques. Catalytic studies showed that the bis(NHC)–Pd complexes are highly active in the Buchwald–Hartwig amination reaction.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► In this work we examine novel ortho xylyl linked palladium carbene complexes. ► We studied as catalysts for amination reaction. ► We conclude that Pd-NHC complexes are very efficient for amination of brombenzene.