engleski

Influence of the rigid spacer to macrocyclization of poly(thialactones): Synthesis and computational analysis

The chemistry of thiamacrocyclic and related ligands is an area of chemistry that has recived much attention over recent years because of the ability of these macrocycles to coordinate transition metal ions strongly and stabilize unusual oxidation states and geometries. Since a major aspect of research in macrocycles is controling selectivity, various modifications have been made to the basic crown thiaether structures in attemnpt to enhance the selectivity of these ligands and the stabilities of complex formed. Among these modifications are the inclusions of different moieties in the polyether ring. However, the main problem arising during the synthesis is competition between intra- and intermolecular reactions leading to form oligomers. Factors that control macrocyclization have been interpreted in terms of activation energy in the ring being formed, and in terms of entropy, related to probability of end-to-end encounters required for reaction. In order to understand the structural and energetic factors controlling the formation of the ring and binding selectivity of macrocyclic ligands towards transitions and heavy metal ions, a series of novel thiamacrocyclic ligands with bulky polycyclic vs. open-chain units were synthesized. Novel macrocyclic thialactones were prepared through coupling reaction of corresponding stannapolythiane, as activated dithiole, with 1, 3-adamantandiyl, glutaryl and pimeloyl dichloride. To investigate the role of the spacer in the cyclization as well as the conformational freedon of ligands, Monte Carlo conformational search was performed using MacroModel program package. The results obtained by analysis of the force field energy components, such as conformational, van der Waals, electrostatic and the solvation energy terms, as well as of conformational entropy expressed as the number of conformations found during the search, confirmed that the size of the ring to be formen and backbone rigidity have important influence on the cyclization.

thiamacrocyclic ligands; macrocyclization; macrocyclic thialactones

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