Dinuclear cobalt complexes supported by biphenol and binaphthol-derived bis(salicylaldimine) ligands: synthesis, characterization and catalytic application in β-enaminone synthesis from 1,3-dicarbonyl compounds and aliphatic amines

Abstract

Two new tetradentate ligands, namely, 3,3′-bis[((2,4,6-trimethyl-phenyl)imino)methyl]-[1,1′]-biphenyl-2,2′-diol, H₂L¹ (1), and 3,3′-bis[((2,4,6-trimethylphenyl)imino)methyl]-[1,1′]-binaphthalenyl-2,2′-diol, H₂L² (3), based on 2,2′-biphenol and 2,2′-binaphthol frameworks have been synthesized and characterized. Correspondingly, dinuclear cobalt complexes {Co[3,3′-bis-((R)-iminomethyl)-(1,1′)-biphenyl-2,2′-dioxo]}₂ (2) and {Co[3,3′-bis-((R)-iminomethyl)-(1,1′)-binaphthalenyl-2,2′-dioxo]}₂ (4) (where R = 2,4,6-Me₃C₆H₂) were synthesized via reactions of the respective ligands with tetrahydrate cobalt acetate. The complexes were then characterized by elemental analysis, mass spectrometry, IR, UV-vis, magnetic susceptibility and single-crystal X-ray diffraction analysis. The single-crystal X-ray crystallographic study indicates a distorted tetrahedral geometry for each of the metal ions in 2 and 4. The magnetic susceptibility measurements at varying temperatures (5–300 K) showed that the complexes exhibit weak antiferromagnetic (AF) interactions. Both metal complexes 2 and 4 successfully catalysed the synthesis of β-enaminones from 1,3-dicarbonyl compounds and aliphatic amines under ambient conditions.