Thioureidocalix[6]arenes Pseudorotaxanes

Abstract

Dedicated to Prof. Vincenzo Balzani on the occasion of his 85th birthdayHeteroditopic calix [6]arenes are extensively exploited as synthetic receptors and as molecular components of supramolecular threaded and interlocked structures. We describe the synthesis of two novel calix[6]arene macrocycles, the upper rim of which is functionalized with either two or three phenylthioureido groups. These moieties are excellent hydrogen-bond donors and largely affect the conformation of the macrocycle, both in solution and in the solid state. Alternate conformers are observed in solution, and they give rise to supramolecular chains in the solid state. Moreover, and because of this conformational freedom, also the recognition properties toward the formation of pseudorotaxanes with bipyridiniumbased axles are strongly affected. The number of phenylthioureido units of the macrocyclic host and the nature of the counterions of the bipyridinium guest determine the stability of the complexes. NMR, UV-Vis and electrochemical measurements revealed that very stable 1 : 1 inclusion complexes are formed between the triphenylthioureido calix[6]arene and a bipyridinium guest with tosylate counterions, whereas no complex is observed between the diphenylthioureido macrocycle and a hexafluorophosphate bipyridinium salt.

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

“…Gold(I) catalysts were subsequently fully characterized by NMR analysis and high-resolution mass spectrometry. The conformation of the catalysts, in low polarity solvents, is dominated by the 1,2,3-alternate conformation assumed by the DN intermediate, as previously demonstrated in our recent contributions [ 33 – 34 ]. Hence, the most notable features of 1 H NMR for A (AuCl) 2 are represented by a pattern for the methylene bridging protons in a 1:1:1 integration ratio ( Figure 2 ).…”

Selenoureido Calix[6]arenes: A Novel Platform for Pseudorotaxane Synthesis

“…The formation of two different pseudorotaxane species in a � 2.1 : 1 ratio was thus observed in analogy with parental thioureido analogues. [16] This could be evidenced by the up-field shift of the proton resonances of the aromatic CÀ H and N-CH 2 bond of the bipyridinium salt that split into two sets of signals. Further, because of the threading, methoxy groups suffer a down-field shift of 1.5 ppm, giving rise to three different signals.…”

“…DH + [39] semi-empirical method that implemented empirical corrections for dispersion and hydrogen-bonding interactions and was used successfully by us to model similar pseudorotaxane systems based on TPT calix [6]arenes. [16] The resulting minimised structures were then used as a starting guess for further DFT geometrical optimisation using the meta-GGA-TPSS functional [40] with a def2-SVP basis set. [41] The final energy of the complexes was then determined with the larger def2-TZPV basis set.…”

“…[7][8][9][10][11][12][13][14] Parallelly, our group reported the synthesis of a novel family of calix [6]arenes functionalised with three phenyl(thio)ureido groups at the upper, larger rim of the macrocyclic scaffold (TPU and TPT, Figure 1, a). [15,16] These cavitands were thoroughly studied in the last twenty years and eventually applied to form pseudo-oriented mechanically interlocked molecules. Furthermore, TPU and TPT were exploited to control the directionality of the threading process and as prototypes of stimuli-induced (light and redox) molecular machines.…”

Supramolecular Handshakes: Characterization of Urea‐Carboxylate Interactions Within Calixarene Frameworks

“…[21,22] An important group of molecular containers, especially from an application standpoint, are those assembled in water due to the hydrophobic effect. [23,24] Aside from being used in the field of the development of supramolecular capsules, the knowledge of non-covalent pairing of complementary molecular blocks is nowadays exploited in the concepts of supramolecular Velcro (applied as adhesives, [25][26][27][28] LMW and polymer gels [29,30] ), in modelling of biochemically important processes, [31][32][33] and molecular machines (for example, rotaxanes [34,35] ).…”