Regioselective acylation of aminoresorcinarenes

The acid catalyzed hydrolytic cleavage of the oxazine rings in the readily available tetraoxazine derivatives of resorcinarenes results in tetraaminoresorcinarenes. A similar process applied to C₂-symmetrical bisoxazine resorcinarene tetratosylates affords C_2v-symmetrical resorcinarenediamines. The mild acylation of these resorcinareneamines with BOC-anhydride or para-nitrophenyl ester proceeds selectively at the nitrogen atoms without affecting the hydroxyl groups. Most of the resulting resorcinareneamides are thus obtained in preparative yields and can be easily purified by simple crystallizations. In the crystalline state the compounds obtained are found to bind chloride anions through hydrogen bonds and electrostatic interactions and to display a chiral arrangement of hydrogen bonded functional groups at the wide rim of the macrocycle.     

Chloride anion-induced dimer capsule based on a polyfluorinated macrocycle meta-WreathArene

[1_n]metacyclophanes are a class of important building blocks for supramolecular assembly of artificial capsules. Herein we present the preparation and properties of a novel polyfluorinated macrocycle meta-WreathArene, a C₂-symmetrical [1₄]metacyclophane. Adopting a cone conformation in acetone solution, the macrocycle can form dimer capsules through hydrogen bonds induced by chloride anions. Each dimer capsule consists of two meta-WreathArene and two chloride anions, and has been unambiguously characterized both in solution and in solid state.     

Selective and tuneable recognition of anions using C(3v)-symmetrical tripodal urea-amide receptor platforms

The synthesis and binding investigations of first generation C(3v)-symmetrical hydrogen bonding urea-amide based tripodal receptors, 1-6, with various anions such as acetate, phosphate, sulfate and chloride in DMSO-d(6) are presented. Analysis of the (1)H NMR titrations of 1-6 showed on all occasions the selective formation of 1?:?1 stoichiometries.     

A sterically congested cis‐stilbene and its phosphonium salt precursor

Triphenyl(2,4,5‐trimethoxybenzyl)phosphonium chloride is formed in solvent‐free form by the reaction under anhydrous conditions between triphenylphosphane and 2,4,5‐trimethoxybenzyl chloride, but when it is crystallized from a mixture of ethyl acetate and chloroform in the presence of air it forms a stoichiometric monohydrate, C₂₈H₂₈O₃P⁺·Cl⁻·H₂O, (I). The reactions between the anhydrous phosphonium salt and alkoxy‐substituted benzaldehydes, using Wittig reactions in the presence of potassium tert‐butoxide, provide a series of multiply substituted stilbenes, most of which were assigned the Z configuration on the basis of their NMR spectra. However, no such deduction could be made for the symmetrically substituted (Z)‐2,2′,4,4′,5,5′‐hexamethoxystilbene, C₂₀H₂₄O₆, (II). Compound (II) does in fact have the Z configuration and the molecular geometry provides evidence for steric congestion around the central double bond; in particular, the central alkene fragment is nonplanar, with a C—C=C—C torsion angle of 7.8 (4)°. In hydrated salt (I), the chloride anions and water molecules are linked by O—H...Cl hydrogen bonds to form C₂¹(4) chains; each cation is linked by C—H...O hydrogen bonds to two different chains, so forming a sheet structure. There are no direction‐specific intermolecular interactions in the structure of (II).     

Metal-switching and self-inclusion of functional cavitands

Cavitands bearing both eight (5) and two (13) metal-ligating carboxymethylphosphonate groups on their rims were synthesized by Arbuzov reaction of the corresponding bromoacetamido cavitands with trialkyl phosphites. These exist in the vase conformation in CDCl(3) and are stabilized by a cyclic seam of hydrogen bonds. This structure was also found in the solid state for the octabromoacetamide 4a and diphosphonate cavitand 13 by single-crystal X-ray analysis. Cavitands 5 and 13 form caviplexes in CDCl(3), CD(2)Cl(2), and alcohol solutions with adamantane derivatives 15a,b, quinuclidine 15d, ammonium and phosphonium salts 14, and drugs like ibuprofen 15c, all of which are stable on the NMR time scale at 295 K. NMR spectroscopy reveals that at 223 K octaphosphonate 5b exists in two forms: the major C(4)-symmetrical compound is filled with solvent while the minor species shows intramolecular inclusion of a dialkoxyphosphoryl group. In methanol-d(4) 5 and 13 exist in a lower symmetry vase conformation with self-inclusion of one alkyl group. Interaction of these complexes with La(OTf)(3) results in a change in the conformation of the cavitand from vase to kite with concomitant and quantitative release of the encapsulated guests. Two to three equivalents of the lanthanide salt per equivalent of cavitand 5a-d is necessary for the complete decomplexation of the included guest. The kite and the vase conformers equilibrate slowly on the NMR time scale at 295 K. The addition of good ligands for metal cations (nitrate or CMPO calixarene 16) shifts the equilibrium to the vase-shaped caviplex and allows quantitative control of the binding and release of the guest. The lanthanide complexes of octaphosphonates 5 in methanol-d(4) are velcraplex-like dimers held together by four metal cations.     

Ion‐Pair Recognition of Tetramethylammonium Salts by Halogenated Resorcinarenes

The non‐covalent interactions of different upper‐rim‐substituted C₂‐resorcinarenes with tetramethylammonium salts were analyzed in the gas phase in an Electrospray Ionization Fourier‐transform ion‐cyclotron‐resonance (ESI‐FTICR) mass spectrometer and by ¹H NMR titrations. The order of binding strengths of the hosts towards the tetramethylammonium cation in the gas phase reflects the electronic nature of the substituents on the upper rim of the resorcinarene. In solution, however, a different trend with particularly high binding constants for halogenated resorcinarenes has been observed. This trend can be explained by a synergetic effect originating from the interaction of the halogenated resorcinarenes with the counter anions through hydrogen bonding. This study highlights the importance of weak interactions in recognition processes and points out the benefits of comparing the gas‐phase data with results obtained from solution experiments.     

Hexakis[3‐(aminocarbonyl)pyridinium] decavanadate(V) dihydrate

The structure of the title compound, (C₆H₇N₂O)₆[V₁₀O₂₈]·2H₂O, at 120 (2) K has monoclinic (C2/c) symmetry. The asymmetric unit consists of one half‐decavanadate anion of C_i symmetry, three cations and one water molecule. Each water molecule is hydrogen bonded to two decavanadate anions, thus forming a one‐dimensional chain of anions. The three‐dimensional supramolecular structure is formed by a network of N—H...O, O—H...O and C—H...O hydrogen bonds, in which the cations, anions and water molecules are involved, and by nonparallel‐displaced π‐stacking interactions between pyridine rings. As a result of hydrogen bonding, the carboxamide groups of the cations are somewhat twisted from the pyridine ring plane.     

Hydrogen bonding: Part IX. Low temperature infrared spectra of H4O2F22− and H6O42− cluster anions in tetramethylammonium fluoride and hyd

At 10–20 K the broad room temperature IR bands of the hydrogen bonded cluster anions in tetramethylammonium fluoride and hydroxide monohydrates and monohydrates-d_n are resolved into a number of components. The band patterns are consonant with distortion of formally tetrahedral H₄F₂O₂^2? and H₆O₄^2? ions of T_d point group to C2v and S₄, respectively in a C_4h⁵ unit cell isomorphous with tetramethylammonium hexafluorosilicate. A lattice mode has been identified for each monohydrate.     

Inclusion of Cl− or Br− anions within host framework formed by second-sphere interactions

In this study, we have deliberately utilized the second-sphere coordination approach into the construction of supramolecular inclusion solids Cl ? [H₂ L1]·[InCl₄] (Crystal I) and Br ? [H₂ L1]·[TeBr₆] (Crystal II). The chloride or bromine anions can be encapsulated inside the host assemblies formed by the diamine molecule (4,6-dimethyl-1,3-phenylene) bis(N,N-dibenzylmethane) (L1) and the metal complexes ([InCl₄]^? and [TeBr₆]^2?) via second-sphere interactions. The inclusion complexes have been structurally characterized by X-ray crystallography, indicating that weak C–H···Cl and C–H···Br hydrogen bonding synthons play a significant role in the construction of host framework. 2-D networks are formed in both complexes by the interconnection of 1-D networks through the multiple weak hydrogen bonding interactions with [InCl₄]^? or [TeBr₆]^2?. The guest Cl^? or Br^? anions are encapsulated inside the host cages through N–H···Cl hydrogen bonds. The inclusion selectively was studied for the two host assemblies.     

Different supramolecular assemblies in two 1:1 proton‐transfer compounds of sulfobenzoic acids with aromatic amines

Two 1:1 proton‐transfer complexes of sulfobenzoic acids with aromatic amines, namely 4‐[2‐(4‐pyridyl)ethenyl]pyridinium 2‐carboxybenzenesulfonate, C₁₂H₁₁N₂⁺·C₇H₅O₅S⁻, (I), and 1,10‐phenanthrolin‐1‐ium 4‐carboxybenzenesulfonate dihydrate, C₁₂H₉N₂⁺·C₇H₅O₅S⁻·2H₂O, (II), have very different hydrogen‐bonding patterns compared with reported organic sulfobenzoic acid complexes. In (I), two cations and two anions form a four‐molecule loop, in which π–π interactions occur. In (II), the anions and water molecules form a three‐dimensional hydrogen‐bonding network, while the cations only act as pendant components. The water molecules play a central role in the formation of the abundant hydrogen‐bonding architecture in (II). The relative poorness and richness of hydrogen bonds in (I) and (II), respectively, give rise to novel hydrogen‐bonding patterns.     

4-Amino-1,8-naphthalimide-based anion receptors: employing the naphthalimide N-H moiety in the cooperative binding of dihydrogenphosphate

The 4-amino-1,8-naphthalimide-based anion receptor 3 binds dihydrogenphosphate with 1:1 stoichiometry through cooperative hydrogen bonding to a naphthalimide N-H and thiourea N-H groups. This was clearly established from ¹H NMR titration experiments in DMSO-d₆ where a substantial shift in the resonance for the naphthalimide N-H was observed concomitant with the expected thiourea N-H chemical shift migration upon successive additions of H₂PO₄⁻. However, whilst ¹H NMR titration experiments indicate that 3 was capable of binding other anions such as acetate, the naphthalimide N-H does not participate and the N-H resonance was essentially invariant during the titration. The lack of cooperative binding in this instance was justifiable on steric grounds.     

Dual Role of the 1,2,3‐Triazolium Ring as a Hydrogen‐Bond Donor and Anion–π Receptor in Anion‐Recognition Processes

Several bis(triazolium)‐based receptors have been synthesized as chemosensors for anion recognition. The central naphthalene core features two aryltriazolium side‐arms. NMR experiments revealed differences between the binding modes of the two triazolium rings: one triazolium ring acts as a hydrogen‐bond donor, the other as an anion–π receptor. Receptors 9²⁺?2BF₄ ^? (C₆H₅), 11²⁺?2BF₄ ^? (4‐NO₂?C₆H₄), and 13²⁺?2BF^4? (ferrocenyl) bind HP₂O₇^3? anions in a mixed‐binding mode that features a combination of hydrogen‐bonding and anion–π interactions and results in strong binding. On the other hand, receptor 10²⁺?2 BF₄ ^? (4‐CH₃O?C₆H₄) only displays combined Csp₂?H/anion–π interactions between the two arms of the receptors and the bound anion rather than triazolium (CH)⁺???anion hydrogen bonding. All receptors undergo a downfield shift of the triazolium protons, as well as the inner naphthalene protons, in the presence of H₂PO₄^? anions. That suggests that only hydrogen‐bonding interactions exist between the binding site and the bound anion, and involve a combination of cationic (triazolium) and neutral (naphthalene) C?H donor interactions. Theoretical calculations relate the electronic structure of the substituent on the aromatic group with the interaction energies and provide a minimum‐energy conformation for all the complexes that explains their measured properties.     

Structural characterization of a new decavanadate compound with organic molecules and inorganic ions

A new decavanadate compound V₁₀O₂₈[Co(H₂O)₆]₃(C₈H₁₈O₆N₂S₂)₂ (I) is synthesized and characterized by single crystal X-ray diffraction, thermogravimetric analysis, FT-IR spectroscopy, and scanning electron microscopy. The sizes of the monoclinic unit cell are as follows: a = 13.2851(16) ?, b = 22.769(3) ?, c = 13.1883(16) ?, ??= 117.555(2)°, V = 3536.7(7) ?³, C2/m space group, Z = 2. The studies revealed that different moieties in the compound show a three-dimensional framework structure, in which {CoO₆}, the decavandate cluster anions, and 1,4-piperazinediethanesulfonic acid (PIPES) interact with each other by intermolecular forces and strong hydrogen bonding. Bond valence calculations were used to calculate the valence states of the atoms.     

Chiral Pt(II)/Pd(II) pincer complexes that show C-H?Cl hydrogen bonding: Synthesis and applications to catalytic asymmetric aldol and silylcyanation reactions

A chiral C₂-symmetric NCN ligand, (5R,7R)-1,3-bis(6,6-dimethyl-5,6,7,8-tetrahydro-5,7-methanoquinolin-2-yl)benzene has been synthesized. A direct cyclometalation of this ligand with K₂MCl₄ (M = Pt, Pd) in dry acetic acid offered the corresponding pincer complexes, [(5R,7R)-1,3-bis(6,6-dimethyl-5,6,7,8-tetrahydro-5,7-methanoquinolin-2-yl)phenyl]platinum(II) chloride 5a and its palladium(II) analogue 5b. The Pt(II) and Pd(II) complexes 5 were characterized by NMR spectroscopy, and X-ray crystal structure analysis was done for the Pt(II) complex. The NMR data for both the complexes and X-ray crystal structural data for the chloro-Pt(II) complex indicate the existence of intramolecular C-H?Cl hydrogen bonding both in solution and in solid states. Chloride abstraction from 5a by treatment with silver triflate resulted in the corresponding triflate complex 6a, which generates the corresponding cationic aqua complex 7a in the presence of water molecules. The Pt(II) complex 6a/7a was used as asymmetric catalyst in the aldol reaction between methyl isocyanoacetate and aldehydes and also in the silylcyanation of aldehydes.     

Effect of <Emphasis Type="Italic">ortho</Emphasis>-methyl groups in the benzene rings of the macrocyclic frame on the chemistry of phosphacavitands

Effect of ortho-methyl groups in the benzene rings of the macrocyclic matrix on the chemistry of cavitands with phosphorous amide bridges in the upper rim is studied. The presence of ortho-methyl groups is shown to prevent formation of phosphacavitands of C _4v symmetry and favor formation of macrocyclic systems of C _2v symmetry, enhance solubility of phosphacavitands in organic solvents, hinder oxidation of phospha(III)cavitands and decrease the yield of phospha(V)cavitands, prevent formation of binuclear molybdenum complexes of phosphorous amide cavitands, and favor formation of their tetranuclear analogs.     

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.     

Facile and efficient synthesis of C2-symmetrical 1,3,5-triazine polycarboxylate ligands under microwave irradiation

A rapid and efficient method for preparation of C₂-symmetrical 1,3,5-triazine polycarboxylate ligands was developed. The reactions included either selective mono- or di-substitution of 2,4,6-trichloro-1,3,5-triazine with various nucleophiles containing carboxyl group(s), followed by nucleophilic displacement of the remained chloride(s) in aqueous media under microwave irradiation. Novel C₂-symmetrical tripodal ligands were afforded in good yields and purities under short reaction time with simple work-up, which are potentially useful as structural directing units in metal-organic frameworks.     

A simple naphthalene-based colorimetric sensor selective for acetate

A new naphthalene based receptor (L) has been designed and synthesized which shows a remarkable color change from colorless to pink on selective binding with acetate. The anion recognition property of the receptor via hydrogen bonding interactions is monitored by UV-vis, fluorescence, and ¹H NMR titrations. It is observed that in each case, the receptor shows a specific selectivity toward the acetate ion over other interfering anions. Thus, a significant bathochromic shift in UV-vis spectrum with a sharp pink color in ‘naked-eye’ makes the receptor suitable for the detection of the acetate ion.     

Thermodynamic and spectroscopic studies on binary mixtures of imidazolium ionic liquids in ethylene glycol

The thermodynamic behaviour of imidazolium based ionic liquids (ILs), 1-butyl-3-methylimidazolium chloride [C₄mim][Cl]; 1-octyl-3-methylimidazolium chloride [C₈mim][Cl], and 1-butyl-3-methylimidazolium methylsulfate [C₄mim][C₁OSO₃] in ethylene glycol [HOCH₂CH₂OH] (EG) have been investigated over the whole composition range at T = (298.15 to 318.15) K to probe the interactions in bulk. For the purpose, volumetric properties such as excess molar volume, $V_m^E$, apparent molar volume, V_?,i, and its limiting values at infinite dilution, $V_{?\text{,}i}^{\infty }$, have been calculated from the experimental density measurements. The molecular scale interactions between ionic liquids and EG have been investigated through Fourier transform infrared (FTIR) and ¹H NMR spectroscopy. The shift in the vibrational frequency for C–H stretch of aromatic ring protons of ILs and O–H stretch of EG molecules has been analysed. The NMR chemical shifts for various protons of RTILS or EG molecules and their deviations show multiple hydrogen bonding interactions of varying strengths between RTILs and EG in their binary mixtures.     

A study of electronic structures of some C9H9- carboanions

The electronic structures of five C₉H₉^-, carboanions have been studied by ab initio STO-3G calculations, and some general conclusions on related C₉H₉^- and C₉H₉⁺ structures are presented. Large antibonding interactions in one occupied MO make barbaral-9-yl anion (2) unstable as its cationic counterpart (8). The proposed D_9h-symmetrical cation and D_3h-symmetrical anion (3) do not exist due to Jahn-Teller distortions. A study of the MO correlations confirms that the two tetracyclic anions with C_2v symmetry (5 and 6) are the results of the Jahn-Teller distortions of 3. Anion 5 is identified as the proper intermediate of the Cope rearrangement of anion 2.