Heteroditopic Calix[6]arene Based Intervowen and Interlocked Molecular Devices

Abstract

Since the dawn of supramolecular chemistry, calixarenes have been employed as platforms onto which functional groups and binding sites can be loaded in a regio‐ and stereocontrolled manner for the recognition of charged and neutral species. Despite their wider annulus, potentially suitable to bind larger guests, the larger members of the calixarene series have been relatively less employed, mainly because of the synthetic difficulties to control their conformational flexibility and their regioselective functionalization. In this account, we will present the achievements gained during the last two decades on the use of the calix[6]arene as a platform to build‐up structures in which the macrocycle acts as a wheel for the synthesis of oriented (pseudo)rotaxanes. We also account on how these calix[6]arene hosts affect the reactivity or spectroscopic properties of their bound guests.

Diametric calix[6]arene-based phosphine gold(I) cavitands

“…Contrarily, calix [6]arene macrocycles are less exploited in catalysis [28]. The larger macrocycle size, its conformational adaptability, and the possibility to selectively functionalize the macrocycle offered several opportunities to design synthetic receptors and prototypes of nanodevices, instead [29]. In this context, we recently devised a new family of triphosphine calix [6]arene gold(I) complexes (Figure 1c) [30].…”

Thioureidocalix[6]arenes Pseudorotaxanes

“…[2] The modular nature of this supramolecular scaffold allows for its regioselective functionalization, leading to the synthesis of non-palindromic wheels, which are currently exploited to construct threaded complexes belonging to the family of (pseudo)rotaxanes. [3] This feature is made possible by a hydrogen-bonding donor (HBD) domain at the upper rim of the calixarene scaffold. Indeed, in low-polarity media, hydrogen-bonding interactions are able to separate the ion-pair of mono-and di-cationic (bi)pyridinium salts, promoting the unidirectional threading of these axles inside the π-rich aromatic cavity.…”

“…In this context, the use of triphenylureido calix [6]arenes (TPU) is well-established (Figure 1 a). [3] It is a matter of fact that the nature and number of HBD -groups appended at the upper rim have an influence on the conformation of the macrocycle and the efficiency of anion-binding. As already mentioned, the complexation of the anions of the electronaccepting guest can govern the direction of threading, which is an important feature in the design of linear molecular motors.…”

“…To this end, we introduced a novel heteroditopic receptor, the diphenylureido calix [6]arene (DPU) which presents only two HBD moieties (Figure 1b). [5] This wheel, which in low-polarity solvents is present as a mixture of 1,2, 3alternate (1,2,3-alt) and cone (C) conformations ( � 4 : 1), is able to thread bipyridinium salts, and the threading process resulted in two different pseudorotaxane systems, P[DPU(1,2,3-alt)�-DOV]2OTs and P[DPU(C)�DOV]2OTs ( � 1 : 1), in solution (Figure 1). Very recently, our group succeeded to control the conformation of calix [6]arene-based pseudorotaxanes as a function of the counterion associated with the viologen salt.…”

Diametric calix[6]arene gold(i) catalysts for intramolecular cyclopropanations of 1,6-dienynes

“…10 The higher flexibility and the possible conformations that they can adopt both in solution and in the solid state render these macrocycles to be highly exploited for molecular recognition or as a component for the synthesis of ( pseudo)rotaxane-based prototypes of molecular machines. 11 These features turned out to be their weaknesses while designing novel catalysts based on this highly modular scaffold. Recently, due to our interest in gold catalysis, we tackled this challenge, and by a suitable functionalisation of the calix [6]arene macrocycle, we described the synthesis of two new phosphine-based gold(I) cavitands.…”