Chemistry of Thioether Macrocyclic Complexes

Abstract

This chapter presents a summary that discusses the coordination chemistry of homoleptic thioether macrocycles critically, with emphasis on likely future developments and uses. Some unpublished results, mainly crystallographic data from laboratories, are discussed in this chapter. The coordination chemistry of thioether ligands has undergone a renaissance over the past five years. This has been because of the observation that cyclic thioethers can bind to a range of transition metal ions to form stable metal complexes. The properties of the M-S(thioether) bond can now be studied with a variety of metal centers, oxidation states, and coordination geometries. Another impetus for the study of the coordination chemistry of crown thioethers stems from the role of thioether binding in biological systems, such as d-biotin (involving tetrahydrothiophene), and blue copper proteins, such as plastocyanin and azurin (involving methionine). The high-yield syntheses of macrocyclic polyoxoethers are characterized by the strong template effects that arise from oxygen coordination by alkali metal ions during cyclization of polyoxo units. The parallel between the binding of soft transition metal ions by soft cyclic thioether ligands and the binding of hard main-group metal ions (Group IA and IIA) by hard cyclic oxyether ligands is presented.