Micellar Effects on the Reduction of 4‐Nitroimidazole Derivative: Detection and Quantification of the Nitroradical Anion

The reductive electrochemistry of 1‐methyl‐4‐nitro‐2‐hydroxymethylimidazole, a 4‐nitroimidazole derivative, was examined in the presence of surfactants anionic as sodium dodecyl sulfate (SDS), nonionic, Triton‐X, Cationic, Hyamine and Cetyl Trimethyl Ammonium Bromide (CTAB). The reductive mechanism of the nitroimidazole derivative was found to be dependent of both, nature and concentration of the surfactants.     

Reduction Removal of Cr(VI) from Wastewater by CO2·- Deriving from Formate Anion Based on Activated Carbon Catalyzed Persulfate

As a strong reducing radical, carbon dioxide anion radical(CO₂^·-) can be generated by initiating sulfate radical(SO₄^·-) in the presence of formate anions(FA) for Cr(VI) reduction. Moreover, activated carbon(AC)-catalyzed persulfate(PS) oxidation is an economically justifiable, environmentally friendly, and easy-to-scale-up method to produce SO₄^·-. The complete removal of Cr(VI) was achieved within 280 min for an initial Cr(VI) concentration of 50 mg/L under the optional condition of c(AC)=1 g/L, [PS]₀=10 mmol/L, [FA]₀=10 mmol/L, T=30℃, and unadjusted pH. When the molar ratio of FA to PS was greater than or equal to 1, the system maintained a strong reduction state. The mechanism investigation confirmed that FA was converted to carboxyl anion radical(CO₂^·-) as the predominant radical for Cr(VI) reduction. This novel system may offer a potential platform technology for Cr(VI) wastewater treatment.     

Electrochemical Approach to the Radical Anion Formation from 2′‐Hydroxy Chalcone Derivatives

Three 2′‐hydroxy chalcone derivatives were electrochemically reduced to the radical anion by a reversible one‐electron transfer followed by a chemical dimerization reaction. Under suitable conditions of the medium, the one‐electron reduction produces very well resolved cyclic voltammograms due to the formation of the radical anion. By using appropriately the wide versatility of the cyclic voltammetric technique, was possible to study the generation of the radical anion and its stability.     

Boron as a Powerful Reductant: Synthesis of a Stable Boron‐Centered Radical‐Anion Radical‐Cation Pair

Despite the fundamental importance of radical‐anion radical‐cation pairs in single‐electron transfer (SET) reactions, such species are still very rare and transient in nature. Since diborenes have highly electron‐rich B? B double bonds, which makes them strong neutral reductants, we envisaged a possible realization of a boron‐centered radical‐anion radical‐cation pair by SET from a diborene to a borole species, which are known to form stable radical anions upon one‐electron reduction. However, since the reduction potentials of all know diborenes (E_1/2=?1.05/?1.55 V) were not sufficiently negative to reduce MesBC₄Ph₄ (E_1/2=?1.69 V), a suitable diborene, IiPr?(iPr)B?B(iPr)?IiPr, was tailor‐made to comply with these requirements. With a halfwave potential of E_1/2=?1.95 V, this diborene ranks amongst the most powerful neutral organic reductants known and readily reacted with MesBC₄Ph₄ by SET to afford a stable boron‐centered radical‐anion radical‐cation pair.     

Halide Anion Mediated Dimerization of a meso‐Unsubstituted N‐Confused Porphyrin

The new N‐confused porphyrin (NCP) derivatives, meso‐unsubstituted β‐alkyl‐3‐oxo N‐confused porphyrin (3‐oxo‐NCP) and related macrocycles, were synthesized from appropriate pyrrolic precursors by a [3+1]‐type condensation reaction. 3‐Oxo‐NCP forms a self‐assembled dimer in dichloromethane that is stabilized by complementary hydrogen‐bonding interactions arising from the peripheral amide‐like moieties. The protonated form of 3‐oxo‐NCP was observed to bind halide anions (F^?, Cl^?) through the outer NH and the inner pyrrolic NH groups, thus affording a dimer in dichloromethane. The structure of the chloride‐bridged dimer in the solid state was determined by X‐ray diffraction analysis.     

Beryllium‐Based Anion Sponges: Close Relatives of Proton Sponges

Through the use of high‐level ab initio and density functional calculations it is shown that 1,8‐diBeX‐naphthalene (X=H, F, Cl, CN, CF₃, C(CF₃)₃) derivatives behave as anion sponges, very much as 1,8‐bis(dimethylamino)naphthalene derivatives behave as proton sponges. The electron‐deficient nature of the BeX substituents, which favors strong charge transfer from the anion towards the former, results in anion affinities that are among the largest ones reported for single neutral molecules.     

Anion Responsive Imidazolium‐Based Polymers

Stimuli responsiveness in polymer design is providing basis for diversely new and advanced materials that exhibit switchable porosity in membranes and coatings, switchable particle formation and thermodynamically stable nanoparticle dispersions, polymers that provide directed mechanical stress in response to intensive fields, and switchable compatibility of nanomaterials in changing environments. The incorporation of ionic liquid monomers has resulted in many new polymers based on the imidazolium group. These polymers exhibit all of the above‐articulated material properties. Some insight into how these anion responsive polymers function has become empirically available. Much opportunity remains for extending our understanding as well as for designing more refined stimuli‐responsive materials.     

Anion Recognition with Hydrogen‐Bonding Cyclodiphosphazanes

Modular cyclodiphosph(V)azanes are synthesised and their affinity for chloride and actetate anions were compared to those of a bisaryl urea derivative ( 1 ). The diamidocyclodiphosph(V)azanes cis‐[{ArNHP(O)(μ‐tBu)}₂] [Ar=Ph ( 2 ) and Ar=m‐(CF₃)₂Ph ( 3 )] were synthesised by reaction of [{ClP(μ‐NtBu)}₂] ( 4 ) with the respective anilines and subsequent oxidation with H₂O₂. Phosphazanes 2 and 3 were obtained as the cis isomers and were characterised by multinuclear NMR spectroscopy, FTIR spectroscopy, HRMS and single‐crystal X‐ray diffraction. The cyclodiphosphazanes 2 and 3 readily co‐crystallise with donor solvents such as MeOH, EtOH and DMSO through bidentate hydrogen bonding, as shown in the X‐ray analyses. Cyclodiphosphazane 3 showed a remarkably high affinity (log[K]=5.42) for chloride compared with the bisaryl urea derivative 1 (log[K]=4.25). The affinities for acetate (AcO^?) are in the same range ( 3 : log[K]=6.72, 1 : log[K]=6.91). Cyclodiphosphazane 2 , which does not contain CF₃ groups, exhibits weaker binding to chloride (log[K]=3.95) and acetate (log[K]=4.49). DFT computations and X‐ray analyses indicate that a squaramide‐like hydrogen‐bond directionality and C_α?H interactions account for the efficiency of 3 as an anion receptor. The C_α?H groups stabilise the Z,Z‐ 3 conformation, which is necessary for bidentate hydrogen bonding, as well as coordinating with the anion.     

Synthesis of Zwitterionic Cobaltocenium Borate and Borata‐alkene Derivatives from a Borole‐Radical Anion

Chemical single‐electron reduction of 1‐mesityl‐2,3,4,5‐tetraphenylborole ( 3 ) gave a stable radical anion [CoCp*₂][ 3 ] as shown in earlier investigations. Herein, we present the reaction of [CoCp*₂][ 3 ] with the 2,2,6,6‐tetramethylpiperidine‐N‐oxyl radical (TEMPO), a common radical trap. Instead of radical recombination, the reaction proceeds through a redox pathway involving oxidation of the borole radical anion combined with reduction of TEMPO. This electron‐transfer process is accompanied by a deprotonation reaction of the cobaltocenium counterion by the base TEMPO^? to give TEMPO‐H and a neutral cobalt(I) fulvene complex ( 7 ). The latter was not observed directly during the reaction, because it instantaneously reacts as a nucleophile attacking at the boron center of the in situ generated borole 3 to give the borate 6 . However, 7 was synthesized independently by deprotonation of [CoCp*₂][PF₆]. In addition, the obtained zwitterionic cobaltocenium borate 6 undergoes a photolytic rearrangement to form the borata‐alkene derivative 9 that thermally transforms to the chiral cobaltocenium borate 12 . Our investigations are based on spectroscopic evidence, X‐ray crystallography, elemental analysis, as well as DFT calculations.     

Formation of Self‐Templated 2,6‐Bis(1,2,3‐triazol‐4‐yl)pyridine [2]Catenanes by Triazolyl Hydrogen Bonding: Selective Anion Hosts for Phosphate

We report the remarkable ability of 2,6‐bis(1,2,3‐triazol‐4‐yl)pyridine ( btp ) compounds 2 with appended olefin amide arms to self‐template the formation of interlocked [2]catenane structures 3 in up to 50 % yield when subjected to olefin ring‐closing metathesis in CH₂Cl₂. X‐ray diffraction crystallography enabled the structural characterization of both the [2]catenane 3 a and the non‐interlocked macrocycle 4 a . These [2]catenanes showed selective triazolyl hydrogen‐bonding interactions with the tetrahedral phosphate anion when screened against a range of ions; 3 a , b are the first examples of selective [2]catenane hosts for phosphate.     

Convenient Synthesis of Various Substituted Homotaurines from Alk‐2‐enamides

Various substituted homotaurines (=3‐aminopropane‐1‐sulfonic acids) 6 were readily synthesized in satisfactory to good yields via the Michael addition of thioacetic acid to alk‐2‐enamides 3 (→ 4 ), followed by LiAlH₄ reduction (→ 5 ) and performic acid oxidation (Scheme 1). The configuration of ‘anti’‐disubstituted homotaurine ‘anti’‐ 6h was deduced from the 3‐(acetylthio)alkanamide (=S‐(3‐amino‐1,2‐dimethyl‐3‐oxopropyl) ethanethioate)‘anti’‐ 4h formed in the Michael addition, which was identified via the Karplus equation analysis, and confirmed by X‐ray diffraction analysis. The current route is an efficient method to synthesize diverse substituted homotaurines, including 1‐, 2‐, and N‐monosubstituted, as well as 1,2‐, 1,N‐, 2,N‐, and N,N‐disubstituted homotaurines (Table).     

Aza‐Bambusurils En Route to Anion Transporters

Previous calculations of anion binding with various bambusuril analogs predicted that the replacement of oxygen by nitrogen atoms to produce semiaza‐bambus[6]urils would award these new cavitands with multiple anion binding properties. This study validates the hypothesis by efficient synthesis, crystallography, thermogravimetric analysis and calorimetry. These unique host molecules are easily accessible from the corresponding semithio‐bambusurils in a one‐pot reaction, which converts a single anion receptor into a potential anion channel. Solid‐state structures exhibit simultaneous accommodation of three anions, linearly positioned within the cavity along the main symmetry axis. The ability to hold anions at a short distance of about 4 Å is reminiscent of natural chloride channels in E. coli, which exhibit similar distances between their adjacent anion binding sites. The calculated transition‐state energy for double‐anion movement through the channel suggests that although these host–guest complexes are thermodynamically stable they enjoy high kinetic flexibility to render them efficient anion channels.     

Formation of Substituted Oxa‐ and Azarhodacyclobutanes

The preparation of substituted oxa‐ and azarhodacyclobutanes is reported. After exchange of ethylene with a variety of unsymmetrically and symmetrically substituted alkenes, the corresponding rhodium–olefin complexes were oxidized with H₂O₂ and PhINTs (Ts=p‐toluenesulfonyl) to yield the substituted oxa‐ and azarhodacyclobutanes, respectively. Oxarhodacyclobutanes could be prepared with excellent selectivity for incorporation of the oxygen atom on the more substituted carbon atom of the alkene. At the same time, azarhodacyclobutanes showed good‐to‐excellent selectivity for heteroatom incorporation on the less substituted carbon. Furthermore, it was shown that steric modifications of the ancillary ligand have a significant influence on the selectivity of Rh–olefin complex formation as well as formation of the substituted azametallacycles.     

A Halogen‐Bonding Bis‐triazolium Rotaxane for Halide‐Selective Anion Recognition

A systematic study on the anion‐binding properties of acyclic halogen‐ and hydrogen‐bonding bis‐triazolium carbazole receptors is described. The halide‐binding potency of halogen‐bonding bis‐iodotriazolium carbazole receptors was found to be far superior to their hydrogen‐bonding bis‐triazolium‐based analogues. This led to the synthesis of a mixed halogen‐ and hydrogen‐bonding rotaxane host containing a bis‐iodotriazolium carbazole axle component. The rotaxane’s anion recognition properties, determined by ¹H NMR titration experiments in a competitive aqueous solvent mixture, demonstrated the preorganised halogen‐bonding interlocked host cavity to be halide‐selective, with a strong binding affinity for bromide.     

Nitrite‐Templated Synthesis of Lanthanide‐Containing [2]Rotaxanes for Anion Sensing

The first anion‐templated synthesis of a lanthanide‐containing interlocked molecule is demonstrated by utilizing a nitrite anion to template initial pseudorotaxane formation. Subsequent stoppering of the interpenetrated assembly allows for the preparation of a lanthanide‐functionalized [2]rotaxane in high yield. Following removal of the nitrite anion template, the europium [2]rotaxane host is demonstrated to recognize and sense fluoride selectively.     

The Radical Anion of Cyclopentasilane‐Fused Hexasilabenzvalene

The radical anion of cyclopentasilane‐fused hexasilabenzvalene was synthesized by the reduction of the corresponding neutral compound. X‐ray crystallographic analysis showed a more trans‐bent structure of the disilene moiety than the neutral compound. Theoretical calculations showed that the highly trans‐bent structure is attributed to the hexasilabenzvalene structure. The EPR spectrum showed that an unpaired electron exists mainly at the disilene moiety. In the UV/Vis spectrum, a large bathochromic shift was observed compared with the neutral compound.     

Anion Binding‐Induced White Light Emission using a Water‐Tolerant Fluorescent Molecular Tweezer

A novel fluorescent molecular tweezer (FMT), built on the pyridine‐2,6‐bis‐carboxamide framework, has been developed that, in presence of a red emitter, gives rise to white light emission in response to the addition of H₂PO₄^? anions. The FMT incorporates two pyrene moieties as fluorescent reporter units and a strategically placed amine residue that imparts pH sensitivity to the fluorescence and offers additional electrostatic/hydrogen‐bonding interactions to the anions. As a result, this FMT selectively binds monoanionic tetrahedral oxyanions such as H₂PO₄^? and HSO₄^? that contain hydrogen bond donors and acceptors, and can sense their presence in aqueous acetonitrile through changes in fluorescence. Anion binding results in excimer formation by the pyrenes and a bluish‐green emission from the FMT. Both amide and amine residues of the FMT interact with these anions. The binding stoichiometry with H₂PO₄^? and HSO₄^? was found to be 1:1 and affinity of the FMT for these anions is of the order of 10⁴ m ^?1. The limit of detection for H₂PO₄^? was found to be 13 nm . Addition of a perylene monoimide‐based red emitter gives rise to panchromatic emission perceived as white light.