Synthesis of diamido-bridged bis-pillararenes and tris-pillararenes for construction of unique rotaxanes and bis-rotaxanes.
ABSTRACT: The pillararene mono- and di(oxyalkoxy)benzoic acids were successfully prepared in high yields by sequential alkylation of ?-bromoalkoxy-substituted pillararenes with methyl or ethyl p-hydroxybenzoate followed by a hydrolytic reaction under basic conditions. Under catalysis of HOBt/EDCl, the amidation reaction of pillararene mono(oxybutoxy)benzoic acid with monoamido-functionalized pillararenes afforded diamido-bridged bis-pillararenes. 1H NMR and 2D NOESY spectra clearly indicated that rotaxanes were formed by insertion of longer diaminoalkylene unit into the cavity of one pillararene with another pillararene acting as a stopper. The similar catalysed amidation reaction of pillararene di(oxybutoxy)benzoic acid with monoamido-functionalized pillararenes resulted in the diamido-bridged tris-pillararenes, which successfully form the unique bis-rotaxanes bearing longer than diaminopropylene diamido bridges.
Project description:Pillar[n]arenes are a new type of macrocyclic compounds, which were first reported in 2008 by Ogoshi. They not only have cylindrical, symmetrical, and rigid structures, but also have many advantages, including easy functionalization and rich host-guest properties. On the other hand, mechanically interlocked molecules (MIMs) exist extensively in nature which have been artificially synthesized and widely applied in the fields of nanotechnology and biology. Although pillararene-based MIMs have been investigated much over recent years, pillararene-based rotaxanes are very limited. In this report, we synthesized a series of amide-linked pillararene-based rotaxanes with ferrocene unit as the stopper. Under the catalysis of HOBT/EDCL, the mono-amido-functionalized pillararenes were amidated with ferrocene carboxylic acid to constructed ferrocene-based rotaxanes, respectively. The structure of the rotaxanes were characterized by 1H NMR, 13C NMR, 2D NMR, mass spectroscopy, and single-crystal X-ray structural determination. In the experiment, the monofunctionalized pillararene was synthesized with a self-inclusion property, which allows for forming a pseudo-rotaxane. The key role is the length of the imine chain in this process. The formation of a rotaxane was realized through amidation of ferrocene dicarboxylic acid, which acted as a plug. In addition, due to the ferrocene units, the pillararene-based rotaxanes perform electrochemically reversible property. Based on this nature, we hope these pillararene-based rotaxanes can be applied in battery devices in the future.
Project description:1,4-dimethoxypillararene undergoes reversible multielectron oxidations forming stable radical cations, a property retained when incorporated in rotaxanes, suggesting that pillararenes can be employed as viable, yet unreported, electron donors.
Project description:A series of mono-amide-functionalized pillararenes with different lengths of N-?-aminoalkyl groups as the side chain on the rim were designed and synthesized, which all formed pseudorotaxanes in the crystal state. And these pseudorotaxanes could be transformed into rotaxanes or open forms in the crystal state. In addition, they were also studied in solution by (1)H NMR spectroscopy.
Project description:The synthesis of "rim-differentiated" C5-symmetric pillararenes, whose two rims are decorated with different chemical functionalities, has remained a challenging task. This is due to the inherent statistical nature of the cyclization of 1,4-disubstituted alkoxybenzenes with different substituents, which leads to four constitutional isomers with only 1/16th being rim-differentiated. Herein, we report a "preoriented" synthetic protocol based on FeCl3-catalyzed cyclization of asymmetrically substituted 2,5-dialkoxybenzyl alcohols. This yields an unprecedented 55% selectivity of the C5-symmetric tiara-like pillararene isomer among four constitutional isomers. Based on this new method, a series of functionalizable tiara-pillararene derivatives with C5-symmetry was successfully synthesized, isolated, and fully characterized in the solid state.
Project description:Rotaxane building blocks bearing 3,5-bis(trifluoromethyl) benzenesulfonate (BTBS) stoppers have been efficiently prepared from a pillararene derivative, 3,5-bis(trifluoromethyl) benzenesulfonyl chloride (BTBSCl) and different diols, namely 1,10-decanediol and 1,12-dodecanediol. The BTBS moieties of these compounds are good leaving groups and stopper exchange reactions could be achieved by treatment with different nucleophiles thus affording rotaxanes with ester, thioether or ether stoppers.
Project description:Two types of mono-ester-functionalized pillararenes, P1 and P2, bearing different side-chain groups, were synthesized. Their host-guest complexation and self-inclusion properties were studied by 1H NMR and 2D nuclear overhauser effect spectroscopy (NOESY) NMR measurements. The results showed that the substituents on their phenolic units have a great influence on the self-assembly of both pillararenes, although they both could form stable pseudorotaxanes at room temperature. When eight bulky 4-brombutyloxy groups were capped on the cavity, instead of methoxy groups, pseudorotaxane P1 became less stable and its locked ester group in the inner space of cavity was not as deep as P2, leading to distinctly different host-guest properties between P1 and P2 with 1,6-dibromohexane. Moreover, pillararene P1 displayed effective molecular recognition toward 1,6-dichlorohexane and 1,2-bromoethane among the guest dihalides. In addition, the self-complex models and stabilities between P1 and P2 were also studied by computational modeling and experimental calculations.
Project description:For a series of neutral rotaxanes consisting of a pillararene ring and axles possessing two stations separated by flexible spacers of different lengths, the free energies of activation for the ring shuttling between the stations were found to be independent of the spacer length. The constitution of the spacer affects the activation energies: replacement of CH2 groups by repulsive oxygen atoms in the axle increases the barrier. The explanation for the observed length-independence lies in the presence of a barrier for re-forming the stable co-conformation, which makes the ring travel back and forth along the thread in an intermediate state.
Project description:Confinement of polymers in nano-spaces can induce unique molecular dynamics and properties. Here we show molecular weight fractionation by the confinement of single polymer chains of poly(ethylene oxide) (PEO) in the one-dimensional (1D) channels of crystalline pillararene. Pillararene crystals are activated by heating under reduced pressure. The activated crystals are immersed in melted PEO, causing the crystals to selectively take up PEO with high mass fraction. The high mass fractionation is caused by the greater number of attractive CH/? interactions between PEO C-H groups and the ?-electron-rich 1D channel of the pillararene with increasing PEO chain length. The molecular motion of the confined PEO (PEO chain thickness of ~3.7?Å) in the 1D channel of pillararenes (diameter of ~4.7?Å) is highly restricted compared with that of neat PEO.
Project description:Control of single-walled carbon nanotube dispersion properties is of substantial interest to the scientific community. In this work, we sought to investigate the effect of a macrocycle, pillararene, on the dispersion properties of a polymer-nanotube complex. Pillararenes are a class of electron-rich macrocyclic hosts capable of forming inclusion complexes with electron-poor guests, such as alkyl nitriles. A hydroxyl-functionalized pillararene derivative was coupled to the alkyl bromide side chains of a polyfluorene, which was then used to coat the surface of single-walled carbon nanotubes. Noncovalent functionalization of carbon nanotubes with the macrocycle-containing conjugated polymer significantly enhanced nanotube solubility, resulting in dark and concentrated nanotube dispersions (600 ?g mL<sup>-1</sup>), as evidenced by UV-vis-NIR spectroscopy and thermogravimetric analysis. Differentiation of semiconducting and metallic single-walled carbon nanotube species was analyzed by a combination of UV-vis-NIR, Raman, and fluorescence spectroscopy. Raman spectroscopy confirmed that the concentrated nanotube dispersion produced by the macrocycle-containing polymer was due to well-exfoliated nanotubes, rather than bundle formation. The polymer-nanotube dispersion was investigated using <sup>1</sup>H NMR spectroscopy, and it was found that host-guest chemistry between pillararene and 1,6-dicyanohexane occurred in the presence of the polymer-nanotube complex. Utilizing the host-guest capability of pillararene, the polymer-nanotube complex was incorporated into a supramolecular organogel.
Project description:Novel water-soluble multifunctional pillararenes containing amide-ammonium-amino acid moiety were synthesized. The compounds demonstrated a superior ability to bind (1S)-(+)-10-camphorsulfonic acid (S-CSA) and methyl orange dye depending on the nature of the substituent, resulting in the formation one-to-one complexes with both guests. The formation of host-guest complexes was confirmed by ultraviolet (UV), circular dichroism (CD) and 1H NMR spectroscopy. This work demonstrates the first case of using S-CSA as a chiral template for the non-covalent self-assembly of architectures based on pillararenes. It was shown that pillararenes with glycine or L-alanine fragments formed aggregates with average hydrodynamic diameters (d) of 165 and 238 nm, respectively. It was established that the addition of S-CSA to the L-alanine-containing derivative led to the formation of micron-sized aggregates with d of 713 nm. This study may advance the design novel stereoselective catalysts and transmembrane amino acid channels.