Regioselective fusion of aromatic di-amines to coordinated 2-(phenylazo)pyridine. An approach to the synthesis of new ligands with large denticity

Abstract

2320-2326Metal mediated oxidative fusion reaction of aromatic di-amines to coordinated 2-(phenylazo)pyridine (pap) ligand in the cationic cobalt complex, [Co(pap)3]2+ affords green complexes of general formula [Co(L)2] (ClO4) [HL = 2-[(N-aryldiamino) phenylazo] pyridine]. In this reaction one of the two amine functions of the di-amine reagent is fused regioselectively to ortho-carbon of the pendant phenyl ring of coordinated pap to yield a bi schelating tridentate ligand while the second amine function remains a pendant and does not take part in the fusion reaction. The crystal structure of one of the representative cobalt complexes, [Co(L2)2] (ClO4) is reported. The structure analysis reveals the presence of two anionic ligands, each of which acts as an N,N,N-tridentate donor. Physicochemical properties of the cobalt complexes are reported. The ligands HL2- HL4 are isolated from the corresponding cobalt complexes by their decomposition. These free ligands showed resolved 1H NMR spectra. The resonance due to -NH and –NH2 in these appeared near 10.5 δ and 4.5 δ, respectively.The ligand HL4 was reacted with salicylaldehyde, which underwent Schiff-base condensation to result an extended ligand H2L5 in a high yield. The 1H NMR spectrum of H2L5 showed the presence of a -CH resonance at 10.6 δ and the -OH resonance at 13.3δ. FAB mass and 1H NMR spectra of the newly synthesized organic ligands indeed confirm their formulations