Congegni Supramolecolari basati sul Threading di Calixareni

Abstract

Recently, Neri et al have introduced an efficient method to obtain endo-cavity complexation and through-the-annulus threading of large calixarenes exploiting the inducing effect of a weakly coordinating anion, tetrakis [3,5-bis (trifluoromethyl) phenyl]borate (TFPB-). In this PhD thesis this approach has been used for the synthesis of [2]rotaxanes, which showed an unprecedented inversion of the wheel orientation. Subsequently, it was extended to the synthesis of pseudo[3]rotaxane systems in which two calix[6]arene macrocycles are threaded by a bis(benzylalkylammonium) axle. Because of the three-dimensional nonsymmetrical nature of the calix[6]arene wheels, in these instances three sequence stereoisomers could be obtained, which were termed as headto- head (H,H), head-to-tail (H,T) and tail-to-tail (T,T). Taking advantage of these systems, it was possible to obtain the stereoprogrammed synthesis of the first examples of calixarene-based [3]rotaxane architectures. The base/acid treatment demonstrated that these systems act as molecular shuttles, which move on a nanometer scale level. The directionality of the threading and the observed high stereoselection have enabled the synthesis of directional calix[6]arene-based catenane. All these aspects represent interesting peculiar features of calixarene threading, which could be exploited for designing molecular machines with new properties or functions