Metal chelates of sulphur-containing polyamine macrocycles and oxygenation of the corresponding cobalt(II) complexes

Abstract

The protonation and complex formation of macrocyclic polyamines containing a sulphur donor atom, 1 -thia-4,7,1O-triazacyclododecane ( L4) and 1 -thia-4,7,11,14-tetra-azacyclohexadecane ( L5), have been investigated with the metal ions Co", Ni", Cu1[, Hgll, and Fell. The equilibrium and kinetic constants for formation of the dioxygen adducts of the cobalt(ii) chelates in aqueous solutions are also reported, and compared with previous data for the analogous macrocycles containing nitrogen, oxygen, and pyridine instead of sulphur. The values of log KML for the macrocyclic polyamines follow the trend N > S > 0. Oxygenation of the cobalt(ii) complexes of L4 and L5 yields p-peroxo-adducts as with the nitrogen and oxygen analogues, and the 0,-affinity order is N 3 S > 0.

Determination of the stability constants of mercury(ii) complexes of mixed donor macrobicyclic encapsulating ligands†

“…For the mixed aza-thia encapsulating ligands, the stability constants (log 10 K[Hg(AMN 3 S 3 sar)] 2ϩ = 17.7; log 10 K[Hg(AMN 4 -S 2 sar)] 2ϩ = 19.5) are approximately ten orders of magnitude less than those of the analogous hexaaza cage molecules (Table 1). 5 The difference does not, however, accord with the differences seen in the case of macrocyclic systems where replacement of a secondary amine donor with a thiaether has little affect on the magnitude of the binding constant (log 10 K[Hg()- [12]aneN 4 )] 2ϩ = 25.5; log 10 K[Hg( [12]aneN 3 S)] 2ϩ = 24.32 and log 10 K[Hg( [16]aneN 5 )] 2ϩ = 27.4; log 10 K[Hg( [16]aneN 4 S)] 2ϩ = 25.15). 16 Kimura has suggested that the macrocyclic effect is limited for large metal ions such as Hg() and that the magnitude of the binding constant is a reflection of the number of secondary amines bound to the metal ion.…”

“…5 The difference does not, however, accord with the differences seen in the case of macrocyclic systems where replacement of a secondary amine donor with a thiaether has little affect on the magnitude of the binding constant (log 10 K[Hg()- [12]aneN 4 )] 2ϩ = 25.5; log 10 K[Hg( [12]aneN 3 S)] 2ϩ = 24.32 and log 10 K[Hg( [16]aneN 5 )] 2ϩ = 27.4; log 10 K[Hg( [16]aneN 4 S)] 2ϩ = 25.15). 16 Kimura has suggested that the macrocyclic effect is limited for large metal ions such as Hg() and that the magnitude of the binding constant is a reflection of the number of secondary amines bound to the metal ion. 17 The enhanced stability of [Hg(sar)] 2ϩ and [Hg(diamsar)] 2ϩ compared with [Hg( [14]aneN 4 )] 2ϩ (Table 1) has thus been attributed to the two extra amine donors in the extra strand of the sar ligand, not to a cryptate effect.…”

Macrocyclic Assembly: A Dive into the Pecking Order and Applied Aspects of Multitalented Metallomacrocycles

“…However, there is scarce information on thiatetraaza compounds. In fact, only one thiatetraaza macrocycle, 1thia-4,7,11,14-tetraazacyclohexadecane, was studied [18]. The different types of macrocyclic ligands are particularly exciting because of the importance in generating new areas of fundamental chemistry and many opportunities of applied chemistry.…”

[15]aneN4S: Synthesis, Thermodynamic Studies and Potential Applications in Chelation Therapy

“…However, there is scarce information on thiatetraaza compounds. In fact, only one thiatetraaza macrocycle, 1-thia-4,7,11,14-tetraazacyclohexadecane, was studied [21]. In the present work, we investigate a 15-membered thiatetraaza macrocyclic compound, 1-thia-4,7,10,13-tetraazacyclopentadecane ([15]aneN 4 S, Figure 1).…”