Conformational Features and Recognition Properties of a Conformationally Blocked Calix[7]arene Derivative

Abstract

The shaping of a calix[7]arene macrocycle into cone-like structure 3, through exhaustive alkylation of doubly bridged calix[7]arene derivative 2 with bulky groups, has been investigated. Conformational details about the structure adopted by calix[7]arene derivative 3 in solution have been obtained by using chemical shift surface maps, as previously reported by our group. Thus, chemical shift contour plots indicated that 3 adopted a cone-shaped structure in solution analogous to that adopted by the known p-tert-butylcalix[7]arene heptacarboxylic acid derivative 4. Interestingly, the X-ray structure of derivative 3 showed a high degree of similarity to the theoretical structure, which confirmed the validity of the contour plots method. The preorganized calix[7]arene host 3 showed interesting recognition abilities toward both organic and alkali cations. In fact, an unprecedented endo-cavity complexation of linear and branched alkyl ammonium cations with a larger calix[7]arene host was evidenced. A comparable affinity for branched tBuNH(3)(+) and linear nBuNH(3)(+) guests was observed.

An intramolecularly self-templated synthesis of macrocycles: self-filling effects on the formation of prismarenes

“…In fact, the hexamer started to appear after 10 min and remains the favored product over time, whereas the equilibrium value of 75 % was reached after 45 min. HPLC analysis (SI) revealed that the pentamer appeared after 15 min but vanished immediately after 30 (30 -45 min). Similar results were observed for the reaction in Scheme 1 starting from propoxy precursor 4c.…”

“…The complexation of N,N,N',N'-tetramethylpiperazonium 7 2+ cation (Scheme 2) showed very interesting features. Addition of 1 equiv of 7 2+ as barfate salt (BArF -) 30,31 to a solution of PrS[6] nPr in CD 2 Cl 2 caused significant changes in its 1 H NMR spectrum (Figure 6), indicative of the formation of 7 2+ @PrS[6] nPr complex with the cation hosted inside the cavity of PrS[6] nPr . Furthermore, in the presence of 7 2+ , a more symmetric conformation of PrS[6] nPr emerged in the 1D and 2D NMR spectra (SI).…”

Directing the Cation Recognition Ability of Calix[4]arenes toward Asymmetric Phase‐Transfer Catalysis

“…Hydrophobic TFPB – , which is known to be a weakly coordinating anion,[32a] was chosen as the counteranion because of the good solubility of its sodium salt in organic solvents. [32b] As previously shown by us,[3a], [4b], [4c] the good solubility of TFPB – salts in CDCl 3 enable the determination of the apparent association constant of the complex by direct integration of its 1 H NMR spectroscopic signals with respect to those of the free host.…”

“…Calix[ n ]arenes are a well‐known class of macrocyclic compounds that have been widely exploited in the last decades as a result of their particular three‐dimensional shape and ease of functionalization The synthetic versatility of calixarene macrocycles makes them suitable for a wide range of applications that include molecular recognition and sensing, synthesis of interpenetrated architectures, biomolecular recognition, and catalysis . It has long been known that calix[4]arene‐amide hosts show a high affinity towards alkali metal cations , .…”

Multiple threading of a triple-calix[6]arene host

“…With respect to the possible types of wheels, more recently, we have introduced the through-the-annulus threading of simple calix[6]arene hosts with dialkylammonium axles [17–26] by exploiting the inducing effect of the superweak tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB) anion that gives free ‘naked’ dialkylammonium cations. In addition, we have reported interesting examples of endo -cavity complexation of alkylammonium cations, as TFPB − salts, inside the aromatic cavity of calixarene [20] and dihomooxacalixarene hosts [21–22]. Thus, through this ‘superweak anion’ approach, we have synthesized interesting examples of calixarene/ammonium-based interlocked structures such as calix-rotaxanes [23–24] and calix-catenanes [25].…”