Appraisal of Ruthenium(II) complexes of (4-phenoxyphenylazo) ligands for the synthesis of primary amides by dint of hydroxylamine hydrochloride and aldehydes

Abstract

A new family of O, N donor-functionalized (4-phenoxyphenylazo)-2-naphthol/4-substituted phenol-based ligands (HL1-HL4) has been synthesized. The prepared ligands were successfully utilized for the access of a series of ruthenium(II) carbonyl complexes of the type [Ru(L)Cl(CO)(EPh3)3] (E = phosphine/arsine), (L = 1-(4-phenoxyphenylazo)-2-naphthol (HL1), 2-(4-phenoxyphenylazo)-4-chlorophenol (HL2), 2-(4-phenoxyphenylazo)-4-methylphenol (HL3) and 2-(4-phenoxyphenylazo)-4-methoxyphenol (HL4)). All of the ruthenium(II) carbonyl complexes and ligands have been fully characterized by FT-IR, UV–visible, 1H NMR, 31P NMR, mass spectrometry and CHN analysis. The ligands have been analyzed by 13C NMR. The UV–visible spectroscopic study reveals that both the ligands and Ru(II) complexes exhibit excellent charge transfer transitions. This is the basic criteria for the oxidative amidation reaction, which is an influential strategy for the transformation of oxygenated organic compounds to the profitable amides. However, this catalytic process makes more impact on the application of new divalent ruthenium(II) azo compounds as catalyst in a single-pot conversion of aldehydes to amides in the presence of NaHCO3.