NNO Pincer Ligand-Supported Palladium(II) Complexes: Direct Synthesis of Quinazolines via Acceptorless Double Dehydrogenative Coupling of Alcohols

A sustainable approach for the synthesis of substituted quinazolines by sequential acceptorless dehydrogenative coupling of 2-aminobenzyl alcohol with alcohols using new Pd(II)-NNO pincer-type complexes as catalysts was reported. Airstable palladium(II) complexes with general formula [Pd(L)(PPh3)] (where L = 4-substituted methyl-2-pyrrolyl benzhydrazone ligands) were synthesized, and their compositions were recognized by analytical and spectral methods (Fourier transform infrared (FT-IR), NMR, and high-resolution mass spectrometry (HRMS)). Single-crystal X-ray crystallography confirmed the tridentate coordination of the ligands and the existence of square-planar geometry around the metal ion. A wide range of substituted quinazoline derivatives was synthesized from double dehydrogenation of benzyl alcohols using 1.5 mol % catalyst loading with a maximum of 93% yield. The formation of aminobenzaldehyde and benzaldehyde intermediates via a double dehydrogenative coupling reaction was confirmed by control experiments.