engleski

Calix[6]arene threading: from Scarcerly to More Preorganized Wheels

The principle of preorganization has become a cornerstone in supramolecular chemistry, because it is used to design highly efficient hosts able to recognize specific guests. In 2010, we reported that scarcerly preorganized (conformationaly mobile) calix[6]arene derivatives were threaded by dialkylammonium axles only when the ammonium cation was associated to the weakly coordinating superweak anion: "the Tetrakis[3, 5- bis(triFluoromethyl)Phenyl]Borate (TFPB-)". In addition, it was observed that the efficiency of the threading was closely associated with the conformational stability of the calix-wheel. Thus, the calix[6]-wheel 1b bearing longer hexyl chains at the lower rim, was threaded by all of the dialkylammonium axles 2-4, more tightly than 1a, as a result of its higher degree of preorganization. Very recently, has been reported a new strategy for the preorganization of calix[6]arene which exploits the functionalization of the methylene bridges (ArCH2Ar) and affords to the formation of stable calix[6]arene cone-conformers. On the basis of these considerations, now the question arises as to wether the calix[6]-wheels 5a-c bearing alkyl groups at the methylene bridges, are also capable of threading with dialkylammonium axles 2-4. In addition, in the present work, we will describe the role played by conformational stability of the derivatives 5a-c on the thermodynamic stability of the respective pseudorotaxanes. Finally, self-sorting experiments with 2+ and calix[6]-wheels 1 and 5 at different degree of preorganization, will be reported.

caixarene ; threading ; complexation ; pseudorotaxanes

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