Reactions of cobalt(ii) chloride and cobalt(ii) acetate with hemisalen-type ligands: ligand transformation, oxidation of cobalt and complex formation. Preliminary study on the cytotoxicity of Co(ii) and Co(iii) hemisalen complexes

Abstract

Several molecular cobalt(II) complexes, one Co(II) coordination polymer and one ionic cobalt(III) complex with imine hemisalen ligands were synthesized. The hemisalen ligands were synthesized from o-vanillin (oVP) and diverse aminopyridines (compounds HL1–HL4) or aminophenol (compound HL5). It was observed that cobalt(II) chloride in dry acetonitrile catalyzes a transformation of HL1 and HL3 instead of complex formation. The conversion of these imines proceeded via self-cyclization to N-2′′-pyridyl-2,6-dioxo-9-aza-[c,g]di-2′-methoxybenzo nonan or its methyl derivative as the major product. The remaining reactions were performed using imines HL1–HL5 and cobalt(II) acetate Co(Ac)₂ in methanol or DMSO/acetonitrile resulting in forming a series of cobalt complexes. The following series of compounds was obtained: two similar tetrahedral molecular Co(II) complexes [Co(L1)₂] and [Co(L3)₂], one trinuclear, mixed-ligand Co₃(Ac)₂(L4)₂(oVP)₂, one coordination polymer {Co(L2)₂}_∞ and finally one octahedral anionic Co(III) complex [HNEt₃][Co(L5)₃]. The latter complex formed in a cobalt(II) acetate reaction with a hemisalen HL5 derived from oVP and 2-aminophenol. The molecular structures of all compounds were confirmed by X-ray diffraction, and the cytotoxicity of Co(II) and Co(III) complexes towards cancer cell lines HCT116, HL-60 and normal cell line MRC-5 was studied.