Triphenylphosphinopalladium(II) complexes with ONO-donor ligands: syntheses, structures and catalytic applications in CC cross-coupling reactions

Abstract

Reactions of 1-((2-hydroxy-5-R-phenylimino)methyl)naphthalen-2-ols (H2Ln, n = 1–3 for R = H, Me, Cl, respectively) with [Pd(PPh3)2Cl2] and Et3N in toluene under reflux produced three new mononuclear square-planar palladium(II) complexes with the general formula [Pd(Ln)(PPh3)] (1, R = H; 2, R = Me; 3, R = Cl). All the complexes were characterized using elemental analysis, solution conductivity and various spectroscopic (infrared, UV–visible and NMR) measurements. Molecular structures of 1, 2, 3 were confirmed using single-crystal X-ray diffraction analysis. In each complex, the fused 5,6-membered chelate rings forming phenolate-O, azomethine-N and naphtholate-O donor (Ln)2− and the PPh3 form a square-planar ONOP coordination environment around the metal centre. Infrared and NMR spectroscopic features of 1, 2, 3 are consistent with their molecular structures. Electronic spectra of the three complexes display several strong primarily ligand-centred absorption bands in the range 322–476 nm. All the complexes were found to be effective catalysts for carbon–carbon cross-coupling reactions of arylboronic acids with aromatic and heteroaromatic aldehydes to form the corresponding diaryl ketones. Copyright © 2016 John Wiley & Sons, Ltd.