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.