Suzuki–Miyaura cross-coupling reaction of aryl bromides catalyzed by palladium(II) pyridoxal hydrazone complexes

The reaction of [PdCl2(PPh3)2] and substituted pyridoxal hydrazone ligands (H2L) in methanol under reflux afford a series of palladium ONO coordinated complexes with general formula [Pd(PPh3)L] (where, L = dianionic terdentate pyridoxal hydrazones). All the palladium complexes are air stable and fully characterized by elemental analysis, spectral and X-ray diffraction methods. In chloroform solution all the metal complexes exhibit characteristic metal to ligand charge transfer (MLCT) absorptions and ligand based transitions. Molecular structure of one of the complexes (3) has been determined by X-ray crystallography indicates that the pyridoxal hydrazone ligands are coordinated to the palladium as a terdentate O, N, O donor and a distorted square-planar geometry is observed around palladium(II) metal center. Further, palladium-catalyzed protocol for Suzuki–Miyaura cross-coupling reactions by the complex (3) has been developed, enabling to obtain biaryl products in good to excellent conversions.

Five new palladium(II) pyridoxal hydrazones complexes have been synthesized and characterized. The single crystal X-ray analysis of complex (3) shows a square-planar geometry around palladium metal. The catalytic activity of one of the complexes in Suzuki–Miyaura cross-coupling of aryl bromides has been studied and was found to be an efficient catalyst.Figure optionsDownload as PowerPoint slideHighlights
► Five new palladium(II) pyridoxal hydrazone complexes with PPh3 have been synthesized.
► Single crystal X-ray structure evidenced a square-planar geometry.
► The catalytic efficiency of Pd(II) complex was explored for S–M cross coupling.