Syntheses, structures and catalytic activities of two cyclopalladated complexes derived from N'-(2-naphthylidene)benzohydrazide

Abstract

Condensation reaction of 2-naphthaldehyde with one equivalent of benzohydrazide in presence of acetic acid in refluxing methanol yielded the Schiff base N'-(2-naphthylidene)benzohydrazide (H2L) in 86% yield. Reaction of equimolar amounts of Li2PdCl4 (generated in situ from PdCl2 and LiCl taken in 1:2 mol ratio), H2L and NaOAc·3H2O in methanol at room temperature provided the complex [Pd(HL)Cl] (1) in 82% yield. Treatment of 1 mol equivalent of 1 with 2 mol equivalents of PPh3 in acetone at room temperature produced the complex [Pd(L)(PPh3)] (2) in 72% yield. The Schiff base and the two complexes were characterized by elemental analysis, mass spectrometric and various spectroscopic (IR, UV–Vis and 1H NMR) measurements. The molecular structures of both complexes (1 and 2) were determined by single crystal X-ray crystallography. In each square-planar complex, the tridentate ligand (HL− in 1 and L2− in 2) acts as pincer-like CNO-donor. The fourth coordination site is occupied by chloride in 1, while that in 2 is satisfied by the P-atom of PPh3. The 2-naphthyl fragment of both HL− and L2− is palladated at the 3-position. Complex 2 was found to be an effective catalyst for one-pot Suzuki-Miyaura double cross-coupling reactions of 3,5-dihalosalicylaldehydes with a variety of arylboronic acids to provide the corresponding triaryl products in moderate to excellent yields.