Thioether free ligands

The low affinity of sulfur for alkali metal ions, however, renders template effects of less consequence in the synthesis of polythia macrocycles. Thus, the competition between cycli-zation and linear polymerization is more statistically defined, with cyclization kinetically favored only at high dilution 64,65,66). Consequently, most of the synthetic methods for the synthesis of polythia rings involve high-dilution techniques coupled with relatively long reaction times. Historically, the study of the coordination chemistry of macrocyclic thioethers has been hindered by difficulties in the synthesis of the free ligands. The synthesis of [BJaneSa, first reported by Ochrymowycz and co-workers in 1977 101), illustrates this well. 

The structure of [CuCl2( [12]aneS3)2] (Fig. 31) shows a distorted octahedral stereochemistry with Cu-Cl = 2.2054(8) A, Cu-S = 2.4474(9), 3.0504(6) A (169). Significantly, the conformation of [12]aneSa in [Cu-Cl2([12]aneSa)2] is almost identical to that of the free ligand this is consistent with the general observation that the kinetic product of thioether coordination involves exo coordination to the metal center. 

A recurrent theme in the coordination chemistry of crown thioethers concerns the interplay between conformational preferences of the ligands and their coordinative behavior. In particular, the structures of complexes result from a compromise between the conformational preferences of the ligands and the electronic requirements of the metal ion. Crown thioethers such as 12S4 show a diminished propensity for chelation because of the exodentate orientation of the S atoms in the free ligand. Exodentate structures reflect the antipathy of most crown thioethers to chelation. As a consequence, complexes with incomplete chelation by the ligand form a substantial fraction of this review. 

Ligands with free amino groups can be immobilized on Afli-Gel 201 and 202 by the EDAC method. Ligands can be attached to Afii-Gel 401 by disulfide, thioester, or thioether formation. Affi-Gel 5C has a high capacity for selectively purifying SH-containing proteins. 

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