Chemistry of selenium/tellurium-containing Schiff base macrocycles

This paper highlights our work to establish a new class of macrocycles based on Schiff base condensation chemistry. The chemistry of a series of azomethine macrocycles, with selenium/tellurium atoms in o-positions with respect to the CN bond is discussed. These are the first Schiff base macrocycles to incorporate selenium or tellurium atom in the ring. The strong stabilization of the 10-E-3 (E = Se/Te) structures of these macrocycles by E–N coordination permits the access to these novel macrocycles by [2+2] template-free condensation of bis(aldehyde) with primary diamines. The success of cyclization has been confirmed by the usual methods of IR, NMR and X-ray structural determinations. After a brief discussion of the synthetic methods adopted for these macrocycles, their complexing abilities toward different metal ions are covered. The macrocyclic polyamine ligands, derived by reduction of the corresponding Schiff bases, readily form complexes with a range of metal ions. This allows a comparison of the properties of complexes of these ligands with those derived from the Schiff bases containing the same denticity but having a different flexibility. The selena- and tellura-macrocycles reported by other groups in the field are also included for comparison. Also discussed is the anion binding studies of some of these macrocycles.

This review focuses on the chemistry of macrocyclic azomethines with selenium or tellurium as donor atoms. The strong E–N(sp2) interaction causes Schiff base macrocycles to have puckered and strained structures, while their reduced analogs have much planar structures due to the weak E–N interaction. This difference in structures gives rise to a very interesting coordination chemistry.Figure optionsDownload as PowerPoint slideHighlights
► The chemistry of azomethine macrocycles with Se/Te is discussed.
► The Se/Te···N interaction permits access to macrocycles by [2+2] template-free condensation.
► The complexing abilities of the ligands toward different metal ions are covered.