Ligand oxidation in N4 tetradentate Schiff base complexes catalyzed by copper(II) hexafluoroacetylacetonate dihydrate: reaction details and structures

Abstract

The ethylene unit connecting the two anilino nitrogen atoms of the copper or nickel complexes of 7,8,15,16,17,18-hexahydro-dibenzo[e,m][1,4,8,11]tetraazacyclotetradecine [H₂(2,2 mac)] and 8,9,16,17,18,19-hexahydro-7H-dibenzo[e,n][1,4,8,12]tetraazacyclopentaadecine [H₂(3,2 mac)], i.e. M(2,2 mac) and M(3,2 mac), are oxidized in chloroform at room temperature under atmospheric conditions in the presence of Cu(hfa)₂·(H₂O)₂ to the oxamide (N–CH₂–CH₂–N– to N–CO–CO–N–). If Cu(hfa)₂·(H₂O)₂ is present in stoichiometric amounts the isolated product of the reaction is the dinuclear complex, M(3,2 oxomac)Cu(hfa)₂. The dinuclear complex can also be prepared by direct reaction of M(3,2 oxomac) (prepared by another method) with Cu(hfa)₂·(H₂O)₂. The dinucleation reaction of M(3,2 oxomac) with M(hfa)₂ is quite general but the ligand oxidation of M(3,2 mac) is specific for Cu(hfa)₂·(H₂O)₂. Reaction of Cu(3,2 mac) with Hhfa or H₂(3,2 mac) with Cu(hfa)₂·(H₂O)₂ results not in oxidation of the macrocycle but in protonation to give Cu{H₂(3,2 mac)}(hfa)₂. The oxidation of Cu(3,2 mac) in an ¹⁸O₂ atmosphere does not result in a significant incorporation of ¹⁸O. However, nearly quantitative incorporation of ¹⁸O is achieved when the reaction is carried out under air in the presence of H₂¹⁸O. The structures of Cu(3,2 mac), Cu(3,2 oxomac), Cu(3,2 oxomac) Cu(hfa)₂ and Cu{H₂(3,2 mac)}(hfa)₂ are reported.