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

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 synthesizedviareactions 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 in2and4. The magnetic susceptibility measurements at varying temperatures (5-300 K) showed that the complexes exhibit weak antiferromagnetic (AF) interactions. Both metal complexes2and4successfully catalysed the synthesis of beta-enaminones from 1,3-dicarbonyl compounds and aliphatic amines under ambient conditions.