Selectively formylated and bridged calix[6]arene derivatives at the upper rim

The strategy of bridging the anisole units at the upper rim of calix[6]arene has been applied to strain the conformations of calix[6]arene. Based on the selective formylation of the 1,3,5-tri-p-tert-butylcalix[6]arene, several new calix[6]arene derivatives with different 1,3-bridged chains or a 1,3,5-tripod bridge at the upper rim have been prepared with moderate yields. The ¹H NMR spectra indicate that these calix[6]arene derivatives adopt a cone conformation, which has also been confirmed by the theoretical calculation at AM1 level. X-ray crystal structure of 1,3,5-tripod bridged compound 5 discloses that the calix[6]arene host stands in a cone conformation with approximate C_3v symmetry, and that a methanol molecule is enclosed in its hydrophobic cavity and stabilized by multi hydrogen bonds.     

Synthesis and application of an efficient calix[4]arene-based anion receptor bearing imidazole groups for Cr(VI) anionic species

We synthesized the new calix[4]arene amines bearing two and four imidazole or tert-butylamine moieties (9a,b/10a,b) by the reaction of di- or tetra-tosylated calix[4]arene derivatives (7 and 8, respectively) with 1-(3-aminopropyl)imidazole and/or tert-butylamine, respectively. After the characterization of 9a,b/10a,b their extraction abilities toward Cr(VI) anionic species (CAS) was evaluated and compared by the liquid–liquid extraction method. The extraction results revealed that calix[4]arene amine having four imidazole groups (10a) was an efficient anion receptor for CAS. Moreover, the extraction of CAS by 10a in the presence of other anions such as Cl^?, NO₃^?, and PO₄^3? showed that 10a could be a selective anion receptor for CAS in the presence of those anions.     

Synthetic and structural studies of [6]-, [7]- and [10]metacyclophanes

A new preparative sequence from 2,3-polymethylene-2-cyclopentenone 5 to 2,6-polymethylenebromobenzenes 3 (n = 6, 7, 10) and 2,6-polymethylenephenyllithiums 6 has been found. The reaction of 6 with various electrophiles produces a number of new compounds to disclose the unique reactivity of the aryl C-Li moiety surrounded by the polymethylene chain. Photolysis of 3a and 3b provides transannular products 8, 10 and 11, all arising from the proximity between the aromatic bromine and the aliphatic hydrogen intraannularly opposed to be removed as HBr. Spectrometric study gives quantitative data of the dependence of the molecular geometry upon the chain length and the aromatic substituents. The energy barriers ΔG_c^≠ of the conformational flipping are 17·4 kcal/mol (T_c 76·5°) for [6]metacyclophane (7a), 11·5 kcal/mol (T_c ?28°) for [7]metacyclophane (7b), ·8 kcal/mol for [10]metacyclophane (7c). The lower-energy process of the aliphatic chain in [6]metacyclophane derivatives is the pseudorotation with substituent-dependent barrier ΔG_c^≠ 11·1 kcal/mol (T_c ?31·5°) for 7a, 12·4 kcal/mol (T_c ?4·5°) for 3a and 12·7 kcal/mol (T_c 1·0°) for 12a. The rather large rotational barrier is attributed to the compressed structure of each system. The benzene ring distortion of the cyclophanes is deduced from the bathochromic shift of the B-band and the diamagnetic shift of the benzene proton signals in the PMR.     

Les cations ammoniums chiraux de type [R1R2R3R4N]+, de nouveaux templates pour les réseaux bimétalliques à pont oxalate

Chiral ammonium cations of the type [R¹R²R³R⁴N]⁺, new templates for a new family of bimetallic oxalate bridged networks. This work deals with the obtention of a new family of bimetallic [R¹R²R³R⁴N][MnCr(C₂O₄)₃] oxalate bridged 2D networks templated by chiral ammonium cations of the type [R¹R²R³R⁴N]⁺, in which R stands for n-alkyl groups from methyl to dodecyl. To cite this article: M. Gruselle et al., C. R. Chimie 6 (2003).     

Large Water-Soluble Cyclophanes with Convergent Intracavity Functionality

New tricyclic spacers, readily available through fourfold Mannich reaction of substituted dibenzyl ketones, were introduced into a series of ten H₂O-soluble cyclophanes with spacious preorganized cavity binding sites. These spacers provide H₂O-solubility with amine or crown-ether functionality remote from the cyclophane cavity while directing functional groups such as keto or OH groups in a precise geometrical array inside the cavity. The cyclophanes were designed to include organic substrates via a combination of apolar and specific polar functional group interactions. The X-ray crystal-structure analysis of the tritopic receptor 18 with one potential neutral-molecule and two cation-binding sites showed a large rectangular open cavity with dimensions of roughly 9 × 14 Å and a spacing of 9.7 Å between the O-atoms of two convergent C?O groups. Despite the binding-site preorganization, cyclophanes incorporating two of the new spacers did not show any substrate binding in aqueous solutions. The failure of these systems to function as receptors is mainly due to steric hindrance to important cyclophane aromatic ring-guest interactions. Also, the favorable solvation of the intracavity functionality may prevent the formation of complexes. Hybrid receptors constructed from the novel spacers and diphenylmethane units were found to bind flat aromatic substrates as well as bulky [4.2]paracyclophanes. The observed large differences in stability (ΔΔG°> 2 kcal mol^?1) of the complexes formed by three structurally closely related hybrid receptors with convergent C?O, OH or CH₂ groups and 6-hydroxynaphthalene-2-carbonitrile as guest can be explained by a strong solvation effect of the convergent functional groups on apolar inclusion complexation.     

Persistance of the Cyclopnane Radical Anions and its Relation to Structure

Reactions of [2_N]cyclophanes (N = 2, ?6) with solvated electrons in 1,2-di-methoxyethane at 193 K have been studied by ESR. and ENDOR. spectroscopy. All but the two most highly bridged cyclophanes (N = 5 and 6) are reduced to paramagnetic species under these conditions. Whereas the radical anions of [2.2]-paracyclophane and [2₃](1,2,4)- and [2₄](l,2,4,5)cyclophanes are sufficiently persistent to be characterized by their hyperfine data, those of the remaining five cyclophanes undergo a rapid cyclization to the radical anions of 4,5,9,10-tetrahydropyrenes. These have been identified as the unsubstituted tetrahydropyrene (from [2.2]-metacyclophane and [2₃](l,2,3)cyclophane), the 2,7-dimethyl-derivative (from [2₃](1,3,5)- and [2₄](l,2,3,5)cyclophanes) and the 1,8-dimethyl-derivative (from (2₄l,2,3,4)cyclophane). The persistence of the cyclophane radical anions seems to depend on the numbers, n_meta and n_para, of the meta-and para-positions of the bridging ethano groups in the two benzene rings. The prerequisite for the radical anion to be persistent is n_meta?n_para.     

A screw-shaped alignment of pyrene using m-calix[3]amide

m-Calix[3]amide bearing three pyrenes (1a) was prepared by the condensation reaction of 3-nonylaminobenzoic acid derivative using Ph₃PCl₂. Pyrenyl groups were found to be aligned in the screw-like fashion by m-calix[3]amide as confirmed by the X-ray crystallography. Aromatic proton signals observed at the up-field region in the ¹H NMR spectrum at low temperature indicated that pyrenyl groups in 1a are aligned in close proximity in THF solution. UV–vis absorption and fluorescence emission spectra did not show marked peak shift nor concentration fluorescence quenching compared with reference compounds implying no significant electronic interaction between pyrenyl groups. These results can be explained by the steric effect of the m-calix[3]amide platform. On the other hand, an excimer emission was observed for m-calix[3]amide having a flexible spacer between pyrene and m-calix[3]amide (1b).     

Epoxidation of tetracyclodecene hydrocarbons with the H<Subscript>2</Subscript>O<Subscript>2</Subscript>·CO(NH<Subscript>2</Subscript>)<Subscript>2</Subscript> adduct in the presence of heteropoly compounds containing rare-earth metal cations

Epoxidation of tetracyclododecene bridged hydrocarbons prepared via the [4+2]-condensation of bicyclo[2.2.1]hept-2-ene and its alkyl derivatives with cyclopentadiene in the presence of Н-form of synthetic mordenite has been studied. Phosphorus-molybdenum and phosphorus-tungsten heteropoly compounds doped with Co³⁺, Gd³⁺, Nd³⁺, Ce(4–x)+ (x = 0, 1) cations as well these compounds deposited on highly disperse carbon material have exhibited high activity in epoxidation of the synthesized hydrocarbons under the action of the H₂O₂·CO(NH₂)₂ adduct. Structures of the new bridged polycyclic epoxides have been elucidated by IR as well as ¹Н and ¹³С NMR spectroscopy.     

Highly stable pseudo[2]rotaxanes co-driven by crown ether-ammonium and donor-acceptor interactions

Bis-p-phenylene-34-crown-10 derivatives 1 and 2, bearing one and two dibenzo[24]crown-8 units, respectively, and 4,4′-dipyridinium derivatives of 3·3PF₆ and of 4·4PF₆, bearing one and two ammonium groups, respectively, have been synthesized from readily available starting materials. ¹H NMR and UV-vis studies reveal that in polar acetonitrile 1 binds 3·3PF₆ to produce pseudo[2]rotaxane 1·3·3PF₆ by making use of one donor-acceptor and one electrostatic interaction, whereas 2 binds 4·4PF₆ to form pseudo[2]rotaxane 2·4·4PF₆ through one donor-acceptor and two electrostatic interactions. The association constants of the two pseudorotaxanes have been determined by the UV-vis titration method to be 9.1 (±1.0)×10³ M⁻¹ and 6.5 (±0.7)×10⁵ M⁻¹, respectively. The high stability of the new pseudo[2]rotaxanes has been ascribed to the cooperative interaction of the two different non-covalent forces.     

Synthesis and characterization of chiral, bridged resorcinarenes as templates for asymmetric catalysis

A full study of the synthesis of chiral, bridged resorcinarenes (3a-3l, 13a, 13b) is presented using Mannich condensation of C_2v-tetraprotected resorcinarenes with chiral 1,n-diamines bearing homochiral α-methylbenzyl auxiliaries at each terminal nitrogen. The study has revealed the methodology to be applicable to preparing a broad range of bridged structures with varying lengths of bridge, different functionality in the bridge and various protecting groups on the upper rim. Reproducible and satisfactory yields in the reaction were only obtained with the pendant R group as methyl. The bridged adducts have been fully characterized by a range of spectroscopic techniques, and NMR has revealed varying trends in the way the various bridges protrude into the cavity. Low temperature NMR as well as X-ray structures of tetramesylate 15 and tetratoluate 3g has revealed hydrogen bonding to the amine nitrogens in the bridge to be an important control element for positioning the bridge relative to the cavity of the bowl. The derivatives provide chiral templates for asymmetric catalysis studies using cooperative effects in the bowl.     

Synthesis of 4‐silaspiro[3.4]octa‐1,5‐diene derivatives: hybrid spiro compounds

Trialkynyl(vinyl)silanes CH₂?CH? Si(C?C? R)₃ (R = Bu, Ph, p‐tolyl) were prepared and treated with 9‐borabicyclo[3.3.1]nonane (9‐BBN). Consecutive 1,2‐hydroboration and intramolecular 1,1‐carboboration reactions (each requires different reaction conditions) were studied. 1,2‐Hydroboration of the Si? vinyl group takes place at ambient temperature (23°C in tetrahydrofuran), followed by intramolecular 1,1‐vinylboration to give 1‐silacyclopent‐2‐ene derivatives, bearing still two alkynyl functions at the silicon atom. Further treatment with a second equivalent of 9‐BBN affords 1‐alkenyl‐1‐(alkynyl)‐1‐silacyclopent‐2‐ene derivatives. These undergo intramolecular 1,1‐vinylboration to give 4‐silaspiro[3.4]octa‐1,5‐dienes bearing the boryl groups at 2 and 6 positions. Protodeborylation of all new compounds (intermediates and final products) using acetic acid in slight excess afforded corresponding silanes including spirosilanes. All compounds were characterized using multinuclear NMR spectroscopy (¹H, ¹¹B, ¹³C, ²⁹Si) in solution state. Solid‐state structures for one of the trialkynyl(vinyl)silanes (R = p‐tolyl) and one of the 1‐silacyclopent‐2‐ene derivatives (R = Ph) were confirmed using X‐ray diffraction. Copyright © 2015 John Wiley & Sons, Ltd.     

Electron impact mass spectrometry of some 2,11-diaza[3.3]cyclophane derivatives

The most significant mass spectral features of thirteen title compounds are discussed with the aid of high-resolution mass measurements and metastable peak analysis. The decomposition patterns of the compounds investigated are strongly affected by N-substitution and by methyl substituents ortho to the bridging chains (ortho effects). A unique feature connected with symmetrical macrocycles, bearing at least two ortho methyl substituents on each phenyl ring, is the presence in their spectra of diagnostically important peaks, corresponding to [M ? RNH₂]⁺˙ and [M ? 2RNH₂]⁺˙ (R = Ts, H, CH₃). These daughter ions are proposed to be associated with the formation of cage compounds (multibridged cyclophanes), generated by an intramolecular [4 + 4] cycloaddition reaction of unstable linear bis-(o-xylylene) precursors.     

DNA binding and photocleavage specificities of a group of tricationic metalloporphyrins

The interactions of 5,10,15-tris(1-methylpyridinium-4-yl)-20-(4-hydroxyphenyl)porphyrinatozinc(II) Zn[TMPyHP]³⁺ (2) along with Cu[TMPyHP]³⁺ (3), Co[TMPyHP]⁴⁺ (4), Mn[TMPyHP]⁴⁺ (5) and the free base porphyrin H₂[TMPyHP]³⁺ (1) with duplex DNA have been studied by using a combination of absorption, fluorescence titration, surface-enhanced Raman spectroscopy (SERS), induced circular dichroism (ICD) spectroscopy, thermal DNA denaturation, viscosity measurements as well as gel electrophoresis experiment. Their binding modes and intrinsic binding constants (K_b) to calf DNA (CT DNA) were comparatively studied and were found significantly influenced by different metals coordinated with the porphyrin plane. Except 3, which has four-coordination structure at the metal, all the metal derivatives showed non-intercalative DNA-binding mode and lower K_b than the free base porphyrin 1, most probably due to the steric hindrance results from the axial ligands of the inserted metals which are five or six-coordination structures. Meanwhile, the insertion of metals into cationic porphyrin greatly removed the self-aggregation of the metal-free porphyrins, and thus fully enhanced the singlet oxygen (¹O₂) productivities in the DNA photocleavage experiments. Therefore, these metalloporphyrins have comparable DNA cleavage ability with the free base porphyrin.     

Syntheses of novel calix[4]arene hydrazone-based receptors and their cooperative complexation with soft and hard metal ions

Four novel calix[4]arene hydrazone-based receptors 3a?Cd were prepared in yields of 69?C87% by condensating formylated calix[4]arene ester (2) with salicylyl hydrazine, 2,4-dinitrophenyl hydrazine, nicotinyl hydrazine or phenyl thiosemicarhazide, respectively. New compounds were characterized through elemental analysis, IR, ESI?CMS, ¹H NMR studies. Compounds 3a?Cd containing two binding sites had the complexation abilities for hard and soft cations concurrently. The noncompetitive extracting experiments showed compounds 3a?Cd were excellent receptors for hard and soft metal cations. The competitive extracting experiments exhibited the cooperative complexation in binding hard and soft metal cations and compound 3a possessed outstanding selectivity for Na⁺ and Hg²⁺. The IR spectra of compound 3a before and after complexation revealed that the soft metal cation was binded in the cavity composed of hydrazone groups and azo groups at the upper rims of calix[4]arene units and hard metal cations was binded in cavity composed of ester groups and phenolic hydroxyl groups at the lower rims of calix[4]arene units.     

Recognition of guests bearing donor and acceptor hydrogen bonding groups by heteroditopic calix[4]arene receptors

The synthesis of new hosts specifically designed for the recognition of neutral guests bearing donor-acceptor hydrogen bonding groups is described. These hosts are characterized by the presence of two distinct binding region in close proximity: the rigid π-donor cavity and the H-bond donor N-methylene-N′-phenylureido group inserted onto the upper rim of the calix[4]arene skeleton. The binding abilities of these receptors were investigated toward a series of neutral ditopic organic molecules in CDCl₃ solution by ¹H NMR spectroscopy. The results obtained show that rigidity of the calix[4]arene apolar cavity is the control element in determining efficiency. In fact, compared with the more rigid 2, host 10, where the rigidity of the cone structure is maintained by hydrogen bonding of the OH of the lower rim, a decrease of efficiency of almost one order of magnitude was observed. The cooperative effect of the two binding region of host 2 was verified with different classes of ditopic guests. Good efficiency in the recognition of urea derivatives and dimethylsulfoxide was achieved.     

Tri- and tetraurea piperazine cyclophanes: synthesis and complexation studies of preorganized and folded receptor molecules

A series of symmetrical tri‐ and tetrameric N‐ethyl‐ and N‐phenylurea‐functionalized cyclophanes have been prepared in nearly quantitative yields (86–99 %) from the corresponding tri‐ and tetraamino‐functionalized piperazine cyclophanes and ethyl or phenyl isocyanates. Their conformational and complexation properties have been studied by single‐crystal X‐ray diffraction, variable‐temperature NMR spectroscopy, and ESI‐MS analysis. The rigid 27‐membered trimeric cyclophane skeleton assisted by a seam of intramolecular hydrogen bonds results in a preorganized ditopic recognition site with an all‐syn conformation of the urea moieties that, complemented by a lipophilic cavity of the cyclophane, binds molecular and ionic guests as well as ion pairs. The all‐syn conformation persists in acidic conditions and the triprotonated triurea cyclophane binds an unprecedented anion pair, H₂PO₄^????HPO₄^2?, in the solid state. The tetra‐N‐ethylurea cyclophane is less rigid and demonstrates an induced‐fit recognition of diisopropyl ether in the solid state. The guest was encapsulated within the lipophilic interior of a quasicapsule, formed by intramolecular hydrogen‐bond‐driven folding of the 36‐membered cyclophane skeleton. In the gas phase, the essential role of the urea moieties in the binding was demonstrated by the formation of monomeric 1:1 complexes with K⁺, TMA⁺, and TMP⁺ as well as the ion‐pair complexes [KI+K]⁺, [TMABr+TMA]⁺ and [TMPBr+TMP]⁺. In the positive‐mode ESI‐MS analysis, ion‐pair binding was found to be more pronounced with the larger tetraurea cyclophanes. In the negative mode, owing to the large size of the binding site, a general binding preference towards larger anions, such as the iodide, over smaller anions, such as the fluoride, was observed.     

Complexation and extraction of non-ferrous metals by calix[n]arene phosphine oxides

The extraction of non-ferrous metal (M²⁺) nitrates by the calix[4,6]arenes (L), bearing four or six phosphine oxide donor groups at the upper or at the lower rim, was quantitatively described in the form of [M_n(NO₃)_2nL] (n = 1, 2) complexes. The extraction constants (Zn²⁺ > Cu²⁺ > Co²⁺ > Ni²⁺) for the both types of L coincide with Irving-Williams sequence. Calix[4]arenes, phosphorylated at the lower (narrow) rim, provide better stability of ML complexes because of the best spatial fitting of M²⁺ by the donor groups. For the upper (wide) rim phosphorylated calix[4]arenes M₂L and ML₂ complexes are more stable. Unusual zwitterionic [Co₂(NO₃)₄L] complex of the lower rim tetraphosphorylated calix[4]arene 1 was determined by X-ray structural analysis.     

[2.2.2.2](2,7)‐1‐Bromonaphthalenophane from a Desymmetrized Building Block Bearing Electrophilic and Masked Nucleophilic Functionalities

In search of 2,7‐ethylene‐bridged naphthalenophanes with desymmetrized naphthalene cores as inherently chiral cyclophanes, nucleophilic substitution of 1‐bromo‐7‐(bromomethyl)‐2‐[(trimethylsilyl)methyl]naphthalene, a desymmetrized building block bearing an electrophilic group (CH₂Br) and a masked nucleophilic functionality (CH₂TMS) which can be activated by fluoride anion, was examined. As a result, in contrast to the case of parent naphthalenophanes wherein the smallest [2.2]naphthalenophane was obtained as the major product, only [2.2.2.2](2,7)‐1‐bromonaphthalenophane was obtained albeit in low yields, whereas the corresponding [2.2]‐ or [2.2.2]naphthalenophanes were not obtained. Though the [2.2.2.2]‐1‐bromonaphthalenophane can adopt four idealized geometries of different symmetry, among which three are inherently chiral, theoretical calculations predict that three conformers have almost equal energy and may equilibrate in solution. The X‐ray crystallographic study shows that it adopts a C₂ conformation with anti,anti,anti orientation of the C?Br bonds at least as a major component in crystal.     

Synthesis,structures and fluorescent properties of two novel lanthanide [Ln = Ce(III), Pr(III)] coordination polymers based on 1,3-benzenedicarboxylate and 2-(4-methoxyphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline ligands

Two structurally diverse coordination polymers [Ce₂(m-BDC)₂(m-HBDC)₂(MOPIP)₂·3/2H₂O]_n (1) and [Pr₂(m-BDC)₃(MOPIP)₂·H₂O]_n(2) have been synthesized by hydrothermal reaction of lanthanide chloride with mixed ligands benzene-1,3-dicarboxylic acid and 2-(4-methoxyphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (MOPIP). The crystal structures of the complexes are zipper-like chains of octacoordinate Ln³⁺ ions, in which Ln³⁺ ions are bridged in different coordination modes by m-BDC²⁺ and decorated by MOPIP ligands. These chains are further assembled into three-dimensional supramolecular framework by π⋯π stacking and hydrogen bonding interactions. The fluorescent property and thermal stability were also investigated. Additionally, Natural bond orbital (NBO) analysis of complex 2 shows a weak covalent interaction between the coordinated atoms and Pr³⁺ ions.     

Ion-pair complexes with strong near infrared absorbance: Syntheses,crystal structures and spectroscopic properties

Three ion-pair complexes, [4-NH₂-Py]₂[M(mnt)₂] (4-NH₂-Py¹⁺ = 4-amino-pyridinium; mnt^2? = maleonitriledithiolate; M = Pt (1), Pd (2) or Ni (3)), have been synthesized and characterized. In the crystal of 1, the strong H-bonding interaction was found from the protonated N-atom of pyridinium to the CN group of [Pt(mnt)₂]^2? together with a weak Pt…H interaction between the anion and the cation. The crystals of 2 and 3 are isostructural with very similar lattice parameters and packing structures, which are distinct from the crystal of 1. Two kinds of strong H-bonding interactions are observed in the crystals of 2 and 3 between the CN groups of [M(mnt)₂]^2? anion and the protonated N-atom of 4-NH₂-Py¹⁺ cation as well as the CN groups of [M(mnt)₂]^2? anion and the amino group of 4-NH₂-Py¹⁺ cation. Complex 1 shows an intense near-IR absorbance in acetonitrile and solid state, such an absorption band is probably assigned to IPCT transition as well as a trace amount of [Pt(mnt)₂]^1? species; complex 3 possesses a weak near-IR absorption band which can be attributed to the mixture of d–d transition in [Ni(mnt)₂]^2? and IPCT transition as well as a trace amount of [Ni(mnt)₂]^1? species.