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

Abstract

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 , 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(II)(2)(L1)(Cl)](ClO(4))(2)}(infinity) 4. Transmetallation of 4 with three equivalents of copper(II) perchlorate produces Cu(II)(3)(L1)(OH)(ClO(4))(4) 5. 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)(H(2)L2)](ClO(4))(2) 6 and [Ba(II)(H(2)L3)](ClO(4))(2) 7, respectively. Copper(II) acetate templates the formation of the crystallographically characterised unsymmetrical macrocyclic complex [Cu(II)(3)(L4)(OH)(NCS)(2)].EtOH, 8.EtOH, from 3, 2,6-diformyl-4-methylphenol and NaNCS.

Macrocyclic coordination chemistry

“…114 Synthetic routes to compartmental ligands with unsymmetric head groups, such as L 81 , were developed by Brooker and co-workers, and involved the initial production of 'two arm' precursors which were then cyclised in metal ion template reactions. 115 Template synthesis of a new macrocyclic ligand L 82 based on the condensation reaction of 2,6-diaminopyridine with an ether linked bis(formyl phenol) was used to produce a series of metal complexes with first row transition metals, lead(II) and lanthanum(III). 116 The copper(II) complex was shown to be bimetallic and the remaining compounds monometallic.…”

Transmetalation for Flexible Pendant-Armed Schiff-Base Macrocyclic Complexes Influenced by Halide Effects

“…In addition, this synthetic strategy makes possible the access to certain metal complexes which could not be obtained by the direct template route . As for the in situ metal-ion exchange of Schiff-base metal macrocyclic complexes, some pioneering works have been done on rigid mononuclear and dinuclear complexes bearing 2,6-diformyl-4-substituted phenol-, pyridine-, salphen-, or salen- based ligands. However, studies on Schiff-base macrocyclic complexes with larger and more flexible multidentate ligands have not been documented yet.…”