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.