Thiacalix[4]arenes contain four aromatic units connected by sulphur atoms. This contribution will be focused especially on two series of 1,3-alt-conformers bearing one or more nitro groups as electrochemical probes.
The first series consists of eight para-tetranitro derivatives which resemble each other in their electrochemical response: first two two-electron reversible waves are followed by final step during which a tetrakis(hydroxylamino) derivative is formed. This reduction pattern is analogous to the “standard” methylene-bridged para-tetranitrocalix[4]arenes, where no mutual electron interaction takes place, all nitrogroups are totally indepencent and finally tetraanion tetraradical is formed [1,2].
The second series includes four meta-nitro derivatives. Generally, the electroreductive behaviour of them is more complicated (except the first member which bears only one nitrogroup). Presence of two and three nitro groups in the same molecule in position meta to lower rim (that means in position ortho- and para- towards the thia bridges), exhibit clear intramolecular communication in contrary to the methylene-bridged calixarenes [3]. This phenomenon was confirmed by quantum chemical calculations.
Acknowledgement: This work was supported by the GACR grant No. 13-21704S, by institutional support RVO: 61388955 and by the GAUK project No. 798214. The authors thank prof. Pavel Lhoták for granting the compounds.
References:
[1] Alan Liška, Pavel Vojtíšek, Albert J. Fry, Jiří Ludvík: J.Org.Chem 78 (2013) 10651 – 10656.
[2] Alan Liška, Marco Rosenkranz, Jiří Klíma, Lothar Dunsch, Pavel Lhoták, Jiří Ludvík: Electrochimica Acta 140 (2014) 572 – 578.
[3] Alan Liška, Karolína Flídrová, Pavel Lhoták, Jiří Ludvík: Monatsh. Chem 146 (2015) 857–862.