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

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.3H(2)O 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 H-1 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 L-2- 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 L-2 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. (C) 2017 Elsevier B.V. All rights reserved.