A new 4-(N,N-dimethylamino)benzonitrile (DMABN) derivative with tetrathiafulvalene unit: modulation of the dual fluorescence of DMABN by redox reaction of tetrathiafulvalene unit

A new derivative of 4-(N,N-dimethylamino)benzonitrile (DMABN) (compound 1) with TTF unit is reported. Compound 1 exhibits dual fluorescence, and moreover the dual fluorescence behavior can be modulated by reversible oxidation and reduction of TTF unit of 1 either chemically or electrochemically. Accordingly, a new molecular fluorescence switch is realized by coupling the features of TTF and DMABN.     

A study of porphin analogues—II: Reactivity indices and spin distribution in some conjugated polyaza macrocycles and their radical ions

Some of the calculated ground state properties of the π-electron system of seven conjugated polyaza macrocyclic ligands are reported, and contrasted with the analogous calculated properties of porphin, tetra-aza porphin and their closed shell dianions.The calculated spin and charge distributions in the anion and cation radicals of the eleven molecules referred to above are also reported in order to assess the perturbation of predicted reactivities by coordination to a central paramagnetic metal ion. The similarity between the Elvidge macrocycle (2) and tetra-aza porphin is particularly noteworthy.     

Preparation and electrical resistivities of tetrathiafulvalen (TTF) and tetraselenafulvalen salts with the [SnR2Cln]2-n anions (n = 3 or 4: R = Et or Ph) and X-ray crystal structure of [TTF]3[SnEt2Cl4]

Tetrathiafulvalen (TTF) and tetraselenafulvalen (TSF) salts with diorganochloro-stannate anions, [TTF][SnEt₂Cl₃] (1), [TTF]₂[SnPh₂Cl₄] (2), [TTF]₃[SnEt₂Cl₄] (3), [TTF]_3.3[SnPh₂Cl₄] (4), [TSF]₂[SnPh₂Cl₄] (5) and [TSF]_3.3[SnPh₂Cl₄] (6), were prepared by the reactions of [TTF or TSF]₃[BF₄]₂ with SnR₂Cl₂ (R = Et or Ph) in the presence of [Ph₃PCH₂Ph]Cl and by electrocrystallization of TTF or TSF in acetonitrile containing SnR₂Cl₂ and [Ph₃PCH₂Ph]Cl. All the salts behave as semiconductors with electrical resistivities of the order of 10–10⁸ Ω cm as compacted samples at 25°C. Electronic reflectance spectra of the simple salts 1, 2 and 5, show a band due to the dimeric(TTF⁺)₂ or (TSF⁺)₂ unit in the 12,200–12,800-cm^?1 region. The complex salt 3 exhibits a TTF⁺/TTF° charge-transfer (CT) band at 8700 cm^?1, and the remaining complex salts, 4 and 6, both display CT bands between the radical cations and between the radical cation and the neutral donor molecule. The crystal structure of 3 was determined by a single-crystal X-ray diffraction. The tetragonal crystal, space group I4cm, has cell dimensions a = 11.710(3) Å, c = 25.242(7) Å, and Z = 4. The structure was solved by the heavy-atom method and refined to a final R value of 0.082 for 479 independent reflections with >F_° > 3σ(F). TTF molecules exist as trimers, in which a slight lateral shift from the eclipsed TTF overlap occurs, although TTF molecules are arranged with equal spacing between them. The trimer units are located perpendicularly to each other, forming a two-dimensional layer. The [SnEt₂Cl₄]^2? anion is disordered with respect to the two SnEt and two SnCl bonds.     

Switching of pseudorotaxanes and catenanes incorporating a tetrathiafulvalene unit by redox and chemical inputs

An acyclic polyether 1a, incorporating a central tetrathiafulvalene (TTF) electron donor unit and two 4-tert-butylphenoxy groups at its termini, has been synthesized. Two macrocyclic polyethers containing two different electron donors, namely a TTF unit with, in one case, a 1,4-dioxybenzene ring (2a), and, in the other case (2b), a 1,5-dioxynaphthalene ring system, have also been synthesized. These two macrocyclic polyethers have been mechanically interlocked in kinetically controlled template-directed syntheses with cyclobis(paraquat-p-phenylene) cyclophane (3(4+)) to afford the [2]catenanes 2a/3(4+) and 2b/3(4+), respectively. X-ray crystallography reveals that the [2]-catenane 2b/3(4+) has the TTF unit of 2b located inside the cavity of 3(4+). The spectroscopic (UV/vis and 1H NMR) and electrochemical properties of compounds 1a, 2a, 2b, 2a/3(4+), and 2b/3(4+) and of the [2]pseudorotaxane 1a.3(4+) were investigated. The absorption and emission properties of the mono- and dioxidized forms of the TTF unit in these various species have also been studied. The results obtained in acetonitrile solution can be summarized as follows. (a) While TTF2+ exhibits a strong fluorescence, no emission can be observed for the TTF2+ units contained in the polyethers and in their pseudorotaxanes and catenanes. (b) A donor-acceptor absorption band is observed upon two-electron oxidation of the TTF unit in the macrocyclic polyethers 2a and 2b. (c) The spontaneous self-assembly of 1a and 3(4+) to give the [2]pseudorotaxane 1a.3(4+) is strongly favored (Kass. = 5 x 10(5) L mol-1) but slow (at 296 K, k = 11.3 L mol-1 s-1 and delta G++ = 15.9 kcal mol-1) because of the steric hindrance associated with the bulky end groups of 1a. (d) In the pseudorotaxane 1a.3(4+), the reversible displacement of the cyclophane from the TTF unit in the threadlike substrate occurs on oxidation/reduction of its electroactive components. (e) Switching between the two translational isomers of the catenanes 2a/3(4+) and 2b/3(4+) occurs by cyclic oxidation and reduction of the TTF unit contained in 2a and in 2b, respectively. (f) Addition of o-chloroanil to the pseudorotaxane 1a.3(4+) and to the catenanes 2a/3(4+) and 2b/3(4+) causes the displacement of the TTF unit from the cavity of the cyclophane 3(4+) because of the formation of an adduct between the TTF unit and o-chloroanil.     

Bis(calixcrown)tetrathiafulvalene receptors

A new class of electroactive receptors has been synthesized, built by covalent association of five subunits: two calixarene platforms for spatial organization, two polyether 3D cavities for cation binding, and one electroactive TTF unit to probe the complexation event. Sodium complexation induces rigidification of the molecular assembly, as shown by 1H NMR titration and single-crystal X-ray crystallographic studies on free receptor 14 and a corresponding complex with two bound sodium atoms per receptor (15-(NaPF6)2). The calixarene units in these receptors change from a pinched cone conformation in the free ligand to a symmetrical cone in the complex. Cyclovoltammetric studies validated the electrochemical recognition concept of these five-member assemblies.     

Ratiometric fluorescence sensing of phenylalanine derivatives by synthetic macrocyclic receptors

The supramolecular analytical behavior of eight pseudopeptidic fluorescent receptors (1a–c, 2a–c, 3, 4) has been studied. The receptors are either macrocyclic or open chain derivatives based on the naphthalene chromophore. The ability of 1–4 for the molecular recognition of amino acids (as Z-protected derivatives) has been evaluated in dichloromethane. The signal observed corresponds to a fluorescence emission of turn-on type. The preferential binding of all the receptors for phenylalanine (Phe) over aliphatic amino acids (Ala, Val) by a factor of 3–4 has been found. Among the family of studied fluorescent molecules, two macrocyclic receptors (1a and 1b) display high exciplex emissions and great fluorescence changes both at long (fluorescence quenching at 390 nm) and short wavelengths (fluorescence enhancement at 340 nm). This feature makes the macrocycles 1a and 1b potentially practical as fluorescent ratiometric sensors for Phe. As a proof of concept, 1a and 1b have been assayed as analytical tools for the identification of model samples enriched with Phe, mimicking the concentrations found in the pathology phenylketonuria (PKU). This result opens the door to the development of new Phe-sensing sensors based on the exciplex signaling mechanism as a new strategy for the analysis of aminoacidemias.     

Synthesis and electrochemical behavior of a model redox-active thiacalix[4]arene-tetrathiafulvalene assembly

Syntheses of the first bisthiacalix[4]arenes systems bridged by a tetrathiafulvalene (TTF) framework have been carried out through triethyl phosphite-mediated dechalcogenation dimerization of the corresponding 1,3-dithiole-2-ones. The cyclic voltammograms of the resulting bisthiacalix[4]arenes tethered by an electroactive TTF unit are provided, and exhibit an electrochemical response in the case of introduction of Ag⁺.     

A Chemically and Electrochemically Switchable [2]Catenane Incorporating a Tetrathiafulvalene Unit

A mechanical switch in a [2]catenane , made up of a cyclobis(paraquat-p-phenylene) tetracation interlocked with a macrocyclic polyether containing a redox-active tetrathiafulvalene (TTF) unit and a 1,5-dioxynaphthalene ring system, can be thrown either chemically or electrochemically. The neutral TTF unit resides “inside” the tetracationic cyclophane in the reduced state and “alongside” it in the oxidized species (TTF⁺/ TTF²⁺). Switching between the reduced (I⁴⁺) and oxidized state (I⁵⁺(I⁶⁺)) is accompanied by a dramatic color change.     

Chiral macrocyclic polyethers incorporating a tetraoxaspiro[5.5]undecane or trioxa-azaspiro[5.5]undecane moiety

New macrocyclic polyethers possessing chirality due to a spiro ring junction are prepared from 2,8-dihydroxymethylated (+)-1,4,7,10-tetraoxaspiro[5.5]undecane 1 and (+)-1,4,7-trioxa-10-azaspiro[5.5]undecane 2, both (E,E). N-Functionalization of compounds derived from 2 is also examined. The complexing properties of representative ligands 3, 4, 5 measured by spectrophotometry in THF, for alkaline and alkaline-earth cations, indicate that these spheric positively-charged species are weakly associated.     

Binaphthalene with substituted tetrathiafulvalene and trichloroquinone: a new example of metal ion-promoted electron transfer

A new binaphthalene (R)-1 with two substituted TTF and trichloroquinone units is reported. Both absorption and ESR spectral studies show that electron transfer occurs between TTF and trichloroquinone units of (R)-1 in the presence of metal ions (Pb²⁺, Sc³⁺, Zn²⁺, and Ca²⁺). We also propose a possible mechanism for this electron transfer process. But, the CD spectral change of (R)-1 in the presence of metal ions is rather small.     

Enantiopure isoplagiochin C by directed deracemization through axis-to-axis chirality transfer

Isoplagiochin C 1 was prepared for the first time in enantiopure form from synthetic racemic material, using a novel stereochemical concept. This macrocyclic bisbibenzyl contains two biaryl axes. Of these, axis A is configurationally stable by its fixation within the macrocyclic framework, while axis B is stereochemically unstable. By diesterification of rac-1 with enantiopure (P)-1,1′-binaphthyl-2,2′-dicarboxylic acid, axis B is locked in its P-configuration, thus allowing the resolution and separate saponification of dilactones (P_A,P_B,P)-3 and (M_A,P_B,P)-3 to give the pure enantiomers of 1. This concept permits recycling of any undesired enantiomer of 1 by thermal equilibration of the respective diastereomer of 3.     

Enantioselective O-acetylcyanation/cyanoformylation of aldehydes using catalysts with built-in crown ether-like motif in chiral macrocyclic V(V) salen complexes

Chiral macrocyclic V(V) salen complexes 1a-f derived from macrocyclic ligands obtained by the reaction of 1R,2R-(−) diaminocyclohexane/(1R,2R)-(+)-1,2-diphenylethylenediamine with bis-aldehydes 2 and 3 were synthesized and used as efficient catalysts in asymmetric cyanation reactions. The V(V) catalysts demonstrated excellent performance (product yields and ees up to 99%) with potassium cyanide (KCN) and sodium cyanide (NaCN). The catalytic system also performed very well with a safer source of cyanide-ethyl cyanoformate to give cyanohydrin carbonates in excellent yield and ee (up to 97%). The V(V) macrocyclic salen complex 1b retained its performance at multi-gram level and was conveniently recycled for a number of times.     

Cryptates—XI: Complexes macrobicycliques,formation, structure,proprietes

The macrobicyclic compounds 1–7 form inclusion complexes with alkali and alkaline-earth metal cations. In these complexes, termed cryptates, the metal cation is contained in the intramolecular cavity of the bicyclic system. The formation, the physical and spectroscopic properties and the structure of these complexes are described and discussed in detail. The formation of some complexes with the macrocyclic ligands 8a–e is also reported.     

Extended TTF-type donors fused with pyrazine units; synthesis and characterization

Pyrazinedicyanoethylthiotetrathiafulvalene, (pzdc-TTF) (1a), an extended TTF fused with a pyrazine moiety and also a dithiolene ligand precursor, was synthesized through a cross-coupling with triethyl phosphite between pyrazine-1,3-dithiole-2-thione (I) and 4,5-bis(2-cyanoethylthio)-1,3-dithiole-2-one (III). This reaction also yields to dipyrazine TTF derivative (1b) and 2,3,6,7-Tetrakis(2-cyanoethylthio)TTF (1c), resulting from the self-coupling reactions of the thione (I) and ketone (III). The crystal structure of 1a is composed by pairs of head to head donor stacks of pzdc-TTF molecules along b in opposite orientations. Single crystals of 1b revealed a new polymorph with a face-to-face π-stacking motif. The electrochemical properties of 1a studied by cyclic voltammetry (CV) in DMF, shows two single electron oxidation processes typical of TTF-based donors; one pair of asymmetric redox waves centered at 627 mV versus Ag/Ag⁺ is ascribed to the couple [pzdc-TTF]⁺/[pzdc-TTF]²⁺, and one pair of quasi-reversible redox waves centered at 430 mV is ascribed to the couple [pzdc-TTF]⁰/[pzdc-TTF]⁺.     

New metal organic frameworks incorporating the ditopic macrocyclic ligand dipyridyldibenzotetraaza[14]annulene

The synthesis and crystal structures of three new metal organic frameworks of type [Zn(L-2H)] _n (1), {[ZnLCl₂](CH₃CN)_0.5(DMF)_0.5(H₂O)_0.5} _n (2) and {[CdL(DMF)(NO₃)₂]·DMF} _n (3), all based on the dipyridyl-derivatised macrocycle, dipyridyldibenzotetraaza[14]annulene (L), are reported along with the X-ray structure of the protonated metal-free ligand as its perchlorate salt, [(HL)(ClO₄)] _n (4). In [Zn(L-2H)] _n , the zinc ion occupies the macrocyclic cavity, being bound to the N₄-donor set of the macrocyclic ring in its doubly deprotonated form. Each zinc atom is also axially bound by a pyridyl moiety from an adjacent complex, resulting in formation of an infinite one-dimensional chain of the ??herringbone?? type in which pairs of macrocyclic complexes interact via face-to-face ?ШC?? stacking interactions. In contrast, the zinc ion in {[ZnLCl₂](CH₃CN)_0.5(DMF)_0.5(H₂O)_0.5} _n does not occupy the macrocyclic cavity but is bound to a pyridyl nitrogen from two ligands such that it acts as a bridge between macrocyclic units and results in the generation of a one-dimensional chain. Two chloro ligands also bind to each zinc centre to yield a distorted tetrahedral coordination geometry. Offset ?ШC?? stacking occurs between adjacent chains involving alternate macrocycles in each chain, giving rise to a zig-zag arrangement. Pairs of interacting chains pass through the above-mentioned chains to generate further ?ШC?? stacking to yield an overall three-dimensional structure that contains large ellipsoidal-shaped channels. In {[CdL(DMF)(NO₃)₂]·DMF} _n the cadmium ion again does not occupy the macrocyclic cavity but acts as a bridge between macrocycles to once again afford a linear chain structure. Each cadmium is bound to two pyridyl groups (arising from different molecules of L), two nitrato ligands and one oxygen-bound dimethylformamide molecule to yield a distorted pentagonal bipyramidal coordination geometry. The protonated ligand, [(HL)(ClO₄)] _n , adopts a linear chain structure in which one pyridyl group is protonated and interacts intermolecularly via a hydrogen bond with the non-protonated pyridyl group of an adjacent macrocyclic unit to yield a hydrogen-bonded linear chain structure.     

On the stability of single-walled carbon nanotubes and their binding strengths

The series of rhenium (I) tricarbonyl mixed-ligand complexes ReCl(CO)₃(H_nbpydt) (n?=?2, 1; n?=?4, 2; bpy?=?bispyridine, dt?=?1,3-dithiole) and ReCl(CO)₃(H_nbpyTTF) (n?=?2, 3; n?=?3, 4; TTF?=?Tetrathiafulvalene) have been investigated theoretically to explore the effect of COOH functional group on their electronic structures, spectroscopic properties and their properties as dye in a solar cell. The calculated geometry structure and absorption spectrum of 1 and 3 are generally consistent with the experimental results. By attaching the COOH groups on both bpy and dt (TTF in 4) moiety in 2, the nature of LUMO is also contributed by both π*(bpy) and π*(dt) (π*(TTF) in 4), and the absorptions have an obvious red shift compared with 1 and 3. In addition, it can be found that the transition terminates at the orbital populated by the COOH-appended moieties, and the performance of 2 and 4 in the dye-sensitized solar cell can be enhanced as compared with 1 and 3.     

Tetrathiafulvalene hydrazone an efficient precursor of various chelating electroactive ligands

Novel bidentate electroactive ligands containing one or two tetrathiafulvalene (TTF) cores as redox active unit have been synthesized thanks to the condensation of various carbonyl derivatives with TTF hydrazone. The electron donating ability of these redox active ligands determined by cyclic voltammetry is described together with the investigations of their molecular structures by X-ray diffraction studies. The chelating ability of these ligands has been exemplified through the coordination to molybdenum carbonyl fragment or the complexation to difluoroboron moiety.     

Coordination Features of a Polyaza-Bipyridine-Macrocyclic Ligand toward Co(II) and Cd(II) in Water and Dimethylsulfoxide

The coordination features of a polyaza macrocycle, containing the diverse bipyridine unit 4,4′-(2,5,6,11,14-pentaaza[15]-[15](2,2′)-bipyridylophane (L3), with Co(II) and Cd(II) have been studied in aqueous solution and in the aprotic solvent dimethylsulfoxide (DMSO). The study was carried out at 298 K by means of potentiometric, spectrophotometric and calorimetric techniques. The formation of the dinuclear species M₂ L3 is observed for Co(II) both in water and in DMSO, whereas Cd(II) is able to form this type of dinuclear complex only in DMSO. The FT-IR spectra of the mononuclear species ML3, formed in both solvents, provide evidence that the rigid structure of the polyaminic chain prevents metal ions from being coordinated by all of the nitrogens of the macrocyclic cavity, in good agreement with the behavior suggested by the thermodynamic parameters. The results are compared with those for the complexation of Co(II) and Cd(II) with similar polyazamacrocycles containing a bipyridine unit directly inside the cavity. Semi-empirical calculations were also performed to obtain structural information.     

Synthesis of the DE-ring of goniodomin A and prediction of its natural relative stereochemistry

Goniodomin A (1) was first isolated from Alexandrium hiranoi as a stereochemically unidentified antifungal agent in 1987 by Murakami. In this study, two stereoisomeric series of non-macrocyclic and macrocyclic DE-ring model compounds of 1 were synthesized, and the natural relative stereochemistry of the DE-ring was predicted by NMR comparison of 1 with these model compounds.     

Convenient synthesis of macrocycles with catechol-type moiety and their neutral boron complexes with pyrene fluorophore for anion sensing

A series of medium ring-sized macrocycles 4a–4e bearing catechol-type moiety were synthesized readily by direct cyclization of di(acid chloride) 1 with diamine derivatives without high-dilution conditions followed by tandem Claisen rearrangement. Complexation of macrocycles 4 with 1-pyrene-boronic acid yielded their corresponding neutral macrocyclic boron complexes 5 with pyrene unit as fluorophore in high yields. Anion sensing properties of these neutral boron complexes were also investigated.