Tricopper(II) complexes of unsymmetrical macrocycles incorporating phenol and pyridine moieties: the development of two stepwise routes

Two stepwise approaches to preparing large unsymmetrical macrocycles incorporating diethylenetriamine lateral units are described: the first utilises protecting group chemistry, whereas the second exploits irreversible amide bond formation in the presence of an excess of the amine. In the first approach condensation of two equivalents of N-acetyldiethylenetriamine 1 with 2,6-diformyl-4-methylphenol, followed by a sodium borohydride reduction of the newly formed imine bonds and acidic removal of the protecting groups, yields a phenol-containing “two-armed” precursor as an HCl salt 2. Using the second approach the new pyridine-containing “two-armed” precursor 3, is prepared from 2,6-dimethylpyridinedicarboxylate and an excess of diethylenetriamine. These two “two-armed” di-primary amine precursors, 2 (after reaction with KOH) and 3, can be condensed with the dicarbonyl head units of choice. The lead templated condensation of 2 with 2,6-diacetylpyridine results in the formation of the macrocyclic dilead(II) complex {[Pb^II₂(L1)(Cl)](ClO₄)₂}_∞4. Transmetallation of 4 with three equivalents of copper(II) perchlorate produces Cu^II₃(L1)(OH)(ClO₄)₄5. Condensation of 3 with 2,6-diacetylpyridine or 2,6-diformylpyridine in the presence of barium(II) ions results in the macrocyclic complexes [Ba^II(H₂L2)](ClO₄)₂6 and [Ba^II(H₂L3)](ClO₄)₂7, respectively. Copper(II) acetate templates the formation of the crystallographically characterised unsymmetrical macrocyclic complex [Cu^II₃(L4)(OH)(NCS)₂]·EtOH, 8·EtOH, from 3, 2,6-diformyl-4-methylphenol and NaNCS.