Rationally Designed Calix[4]arene–Pyrrolotetrathiafulvalene Receptors for Electron-Deficient Neutral Guests

Synthesis of calixresorcarenes using magnetic poly triazine-benzene sulfonamide-SO3H

The purpose of this work is to develop a magnetically recyclable immobilized base catalyst for the green synthesis of calixresorcarenes. To achieve this, poly triazine-benzene sulfonamide (PTBSA) has been coated on magnetic Fe₃O₄ nanoparticles and subsequently chlorosulfonic acid has been supported to obtain Fe₃O₄@PTBSA-SO₃H. The structure of nano-Fe₃O₄@PTBSA-SO₃H was characterized by TEM, XRD, FT-IR, VSM, WDX, EDX, TGA/DSC and FE-SEM. The catalytic efficiency of this catalyst was also investigated in the synthesis of novel calixresorcarene derivatives. The advantages of heterogeneous nature, catalytic activity and the recyclability of the polymer support were also strengthened by advanced surface treatment. These key factors (basic sites, acidic sites and heterogeneity) play essential roles in the catalyst performance. This procedure has some advantages such as short reaction time, clean and fast work-up and easy separation of the catalyst by an external magnet.

Magnetic poly triazine-benzene sulfonamide-SO₃H was investigated for the synthesis of calixresorcarenes.

Sulfoxide hemithioindigo tweezers - visible light addressable capture and release

Introducing responsive elements into supramolecular recognition systems offers great advantages for the control of intermolecular interactions and represents an important stepping stone towards multi-purpose and reprogrammable synthetic systems. Of particular interest is implementation of light-responsiveness because of the unique ease and precision of this signal. Here we present visible light responsive hemithioindigo-based molecular tweezers that bear a highly polar sulfoxide function as an additional recognition unit inside their binding site. Sulfur oxidation allows to simultaneously enhance all crucial properties of this receptor type i.e. photoswitching capability, thermal stability of individual switching states, binding affinity, and binding modulation upon switching. With a novel titration method the thermodynamic binding parameters were determined using reduced sample amounts. Employing these strongly enhanced molecular tweezers allowed to demonstrate photocontrol of intermolecular charge transfer in a reversible manner.

Hemithioindigo based molecular tweezers with a comprehensively improved property profile are obtained by simple oxidation of the sulfur atom.

Metalla-Assembled Electron-Rich Tweezers: Redox-Controlled Guest Release Through Supramolecular Dimerization

Developing methodologies for on-demand control of the release of a molecular guest requires the rational design of stimuli-responsive hosts with functional cavities. While a substantial number of responsive metallacages have already been described, the case of coordination-tweezers has been less explored. Herein, we report the first example of a redox-triggered guest release from a metalla-assembled tweezer. This tweezer incorporates two redox-active panels constructed from the electron-rich 9-(1,3-dithiol-2-ylidene)fluorene unit that are facing each other. It dimerizes spontaneously in solution and the resulting interpenetrated supramolecular structure can dissociate in the presence of an electron-poor planar unit, forming a 1:1 host-guest complex. This complex dissociates upon tweezer oxidation/dimerization, offering an original redox-triggered molecular delivery pathway.

Enantioselective Michael reaction of anthrone catalyzed by chiral tetraoxacalix[2]arene[2]triazine derivatives

A highly enantioselective Michael addition reaction of anthrone with nitroalkenes by chiral tetraoxacalix[2]arene[2]triazine catalysts was investigated as a novel topic. The stereoselective conversion progressed smoothly by employing 10 mol% of the catalyst and afforded the corresponding Michael adducts with acceptable to high enantioselectivities (up to 97% ee) and very high yields (up to 96%).

A highly enantioselective Michael addition reaction of anthrone with nitroalkenes by chiral tetraoxacalix[2]arene[2]triazine catalysts was investigated as a novel topic.

Upper-Rim Monofunctionalisation in the Synthesis of Triazole- and Disulfide-Linked Multicalix[4]- and -[6]arenes

Covalently linked multiple calixarenes are valued in supramolecular chemistry. This work reports an easy and versatile synthetic route to covalently linked double and triple calix[4]arene and calix[6]arenes by a novel DMF-controlled selective alkylation of a convenient and readily available upper-rim dimethylaminomethyl-substituted tetrahydroxy and hexahydroxy calix[4]arene and -[6]arenes. Synthetic routes to upper-rim functionalised redox active disulfide-linked double-, tetra- and peptidohybrid-calixarenes employing either redox chemistry (CH₂ SH) or thiolates (CH₂ S^- ) are also opened up from the same key starting material.

Functionalised tetrathiafulvalene- (TTF-) macrocycles: recent trends in applied supramolecular chemistry

Tetrathiafulvalene- (TTF-) based macrocyclic systems, cages and supramolecularly self-assembled 3D constructs have been extensively explored as functional materials for sensing and switching applications.

Flexible Viologen Cyclophanes: Odd/Even Effects on Intramolecular Interactions

The ability of three bis-viologen cyclophanes to act as redox-triggered contractile switches is investigated. Odd/even effects in the formation of cyclic bis-viologens are circumvented by the use of a Zincke salt intermediate and a tetrathiafulvalene template to prepare a flexible cyclophane with hexyl linkers. Comparative spectro-electrochemical studies of this macrocycle with two other pentyl- or heptyl-linked cyclic bis-viologens show that the development of intramolecular interactions in aqueous solution depends on the length of the bridges. This dependence is confirmed by EPR and DFT studies of the magnetic coupling in the diradical dication species. The anti-ferromagnetic or ferromagnetic nature of the coupling depend, respectively, on the odd or even number of methylene groups in the spacer.

Evidence for an intrinsic binding force between dodecaborate dianions and receptors with hydrophobic binding pockets

A gas phase binding study revealed strong intrinsic intermolecular interactions between dianionic halogenated closo-dodecaborates [B12X12](2-) and several neutral organic receptors. Oxidation of a tetrathiafulvalene host allowed switching between two host-guest binding modes in a supramolecular complex. Complexes of β-cyclodextrin with [B12F12](2-) show remarkable stability in the gas phase and were successfully tested as carriers for the delivery of boron clusters into cancer cells.

Advances in the synthesis of functionalised pyrrolotetrathiafulvalenes

The electron-donor and unique redox properties of the tetrathiafulvalene (TTF, 1) moiety have led to diverse applications in many areas of chemistry. Monopyrrolotetrathiafulvalenes (MPTTFs, 4) and bispyrrolotetrathiafulvalenes (BPTTFs, 5) are useful structural motifs and have found widespread use in fields such as supramolecular chemistry and molecular electronics. Protocols enabling the synthesis of functionalised MPTTFs and BPTTFs are therefore of broad interest. Herein, we present the synthesis of a range of functionalised MPTTF and BPTTF species. Firstly, the large-scale preparation of the precursor species N-tosyl-(1,3)-dithiolo[4,5-c]pyrrole-2-one (6) is described, as well as the synthesis of the analogue N-tosyl-4,6-dimethyl-(1,3)-dithiolo[4,5-c]pyrrole-2-one (7). Thereafter, we show how 6 and 7 can be used to prepare BPTTFs using homocoupling reactions and functionalised MPTTFs using cross-coupling reactions with a variety of 1,3-dithiole-2-thiones (19). Subsequently, the incorporation of more complex functionality is discussed. We show how the 2-cyanoethyl protecting group can be used to afford MPTTFs functionalised with thioethers, exemplified by a series of ethylene glycol derivatives. Additionally, the merits of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as an alternative to the most common deprotecting agent, CsOH·H2O are discussed. Finally, we show how a copper-mediated Ullman-type reaction can be applied to the N-arylation of MPTTFs and BPTTFs using a variety of aryl halides.

Tuning of tetrathiafulvalene properties: versatile synthesis of N-arylated monopyrrolotetrathiafulvalenes via Ullmann-type coupling reactions

An Ullmann-type coupling reaction was employed for the preparation of several N-arylated monopyrrolotetrathiafulvalenes with variable substitution patterns. Spectroscopic and electrochemical properties of the coupling products strongly depend on the electronic nature of the aromatic substituents due to their direct conjugation with the tetrathiafulvalene chromophore. The crystal packing of the arylated monopyrrolotetrathiafulvalenes is primarily defined by networks of C-H···X weak hydrogen bonds and short S···S contacts involving the tetrathiafulvalene moieties.

Enhancement of electron-donating character in alkylated monopyrrolo-tetrathiafulvalene derivatives

Bis-alkyl-substituted monopyrrolo-tetrathiafulvalene (MPTTF) derivatives display stronger affinity to electron-deficient molecular guests in comparison with their non-substituted MPTTF analogues.

Fused glycoluril-tetrathiafulvalene molecular clips as receptors for neutral electron acceptor guests

Glycoluril-based molecular clips incorporating tetrathiafulvalene (TTF) sidewalls have been synthesized, and the efficient binding ability in solution of this host architecture toward m-dinitrobenzene through donor-acceptor interaction has been demonstrated.