Sulfur macrocycles

Although the first all-sulfur macrocycles were prepared many years ago " the first systematic study of such compounds was initiated by Busch and his coworkers , who were interested in the cation binding properties of such ligands. A sequential synthesis was utilized to produce 1,4,8,11-tetrathiacyclotetradecane [tetrathia-14-crown-4 (70)] . In the first step, 1,3-propanedithiol is metallated using sodium and alkylated with 2-chloroethanol. The diol was then treated with thiourea to form the dimercapto-dithioether compound 9. The latter was once again metallated with sodium and allowed to react with 1,3-dibromopropane. The yield of 70 in the ring closure step, conducted at high dilution in absolute ethanol, was 7.5% after recrystallization. The entire sequence is illustrated in Eq. (6.8) . ... 

Although a large number of such compounds have been prepared, many of the mixed nitrogen-sulfur macrocycles are included in other tables, most notably in Chap. 4. Some have also been recorded in Chap. 8 as monocyclic precursors to bi- or polycyclic ligands (i.e., cryptands). The reader is directed to the tables of other chapters where the desired compound, if known, may be reported. 

As well as sulfur, macrocycles containing other large donors such as tertiary phosphorus or arsenic atoms are also known, although the metal-ion chemistry of such ligands has been somewhat less explored. In part, this reflects the synthetic difficulties often encountered in the preparation of ligands containing these heteroatoms structures (49) (Horner, Walach Kunz, 1978), (50) (Kauffmann Ennen, 1981), and (51) (Mealli etal., 1985) provide three representative examples of such macrocycles. 

Complexes with mixed-donor macrocycles and with all-phosphorus and all-sulfur macrocycles 257... 

Table 108 Complexes with Mixed-donor, All-phosphorus and All-sulfur Macrocycles...

Thioether analogs of the crowns have been known since the 1930s,103 but metal ion complexes of these ligands have not been investigated with the intensity found for the crowns and polyaza macrocycles. As anticipated from the soft nature of the heteroatom, the sulfur macrocycles show a preference to bind transition metals rather than alkali and alkaline earth ions. Studies have... 

Table 1 Metal complexes of sulfur macrocycles in order of the metal s position within the periodic system of the elements (PSE) and further according to ring size notification of the complexes is taken from the original references... 

Marianne Roller was born in Bavaria, Germany, in 1958. She did her diploma in chemistry at the Technical University of Munich in 1984 and received her Ph.D. with magna cum laude under Prof. Ivar Ugi in 1989. During the following years, she specialized on instrumental analytics. Since 1995, she has been responsible for the development of GC-MS and LC-MS methods for the detection of chemical warfare agents in biomedical samples (verification) at the German Forces. Sulfur mustard, whose homologues can be used as educts in the synthesis of sulfur macrocycles, is one of her objects of interest. 

The thiethane complex Re2(CO)9(SCH2CH2CH2-) catalyzes the cyclooligomerization of thiethane to the sulfur macrocycles I2S3 and24S6. ... 

The porphyrins constitute another class of nitrogen donor ligands which favor Ag(II) over Ag(I). Their macrocychc stmeture provides strong in-plane ligand fields, which facilitate oxidation of the metal. Phthalocyanine complexes of Ag(II) are very stable and can be oxidized electrochemically to Ag(III) further oxidation gives a Ag(III) phthalocyanine cation radical. The oxidation of Ag(I) complexes of sulfur macrocycles also leads reversibly to Ag(II) complexes. ... 

Results from the correlation of stability constants in conjunction with redox data have led to insights regarding the coordination chemistry of thia macrocycles. For example, the electrochemical behavior of a number of copper(II)/(I) redox couples has been investigated, and redox potentials as well as protonation and stability constants of Cu species were determined for a number of tetradentate and pentadentate thia-derived macrocycles with thia- and mixed thia-aza rings with the basic backbones (51) and (52). Results of the examination of the stability constants in conjunction with the Cu redox potentials indicate that the stability constants for the Cu oxidation state are relatively constant regardless of the mixing in of nitrogen donor atoms. Hence, the dramatic increase in the Cu / redox potential which is observed in the presence of the sulfur macrocycles can be attributed to a destabilization of the Cu state rather than stabilization of the Cu state, contrary to popular belief from the hard-soft acid-base system. 

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