Macrocyclic tetrathia ligands

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) . ... 

Buter and Kellogg 62, 63), large-scale synthesis of thioether macrocycles can now be achieved in good yields (2 77,223,224,226). Octathia Ss-donor macrocycles have been synthesized as 2 -t- 2 products from the cyclization reactions employed to form tetrathia S4-donor ligands 59, 61,83,147,209). 

Figure 7-65 shows the X-ray structure of the complex [7,16-bis(ferrocenylmethyl)-l,4,10,13-tetrathia-7,16-diaza-cyclooctadecane]copper(i), [CuL ] and that of the free ligand L [186]. The copper(i) centre assumes a distorted tetrahedral geometry. With respect to the macrocyclic conformation of the free ligand, which possesses two gauche and two anti C-S-C-C bonds and two anti N-C-C-S bonds, complexation with copper (i) maintains the two gauche and two anti C-S-C-C bonds, but the two N-C-C-S bonds become gauche. 

Fig. 7-65. Crystal structure of (a) the macrocyclic ligand 7,16-bis(ferrocenylmethyl)-l,4,10,13-tetrathia-7,16-diaza-cyclooctadecane (b) one of the three independent molecules of its copper(i) complex (as PFg salt). Cu-S4, 2.27 A Cu-S7, 2.35 A (reproduced by permission of the Royal Society of Chemistry).

The trimethylaluminum complexes of tetraaza macrocycles contain AlMe2 groups and externally coordinated AlMes molecules [416-419] tetrathia macro-cycles [420, 421] are perhaps better described as simple coordination compounds of polydentate ligands, rather than host-guest complexes. This is suggested by the short Al-N distances (ca 2.0 A) and the external coordination of the metal. 

---