Partial Cone Conformation Research Articles

7,15,23-Triphenyl-25,26,27-triethylester-2,3,10,11,18,19-hexahomo-3,9,11-trioxacalix[3]arene in a Partial-Cone Conformation

Reaction of p-phenylhexahomocalix[3]arene (I-H) with bromomethyl acetate and potassium carbonate in acetone leads to the title triester derivative, (I-CH 2 CO 2 Et) {triethyl 7,15,23-triphenyl-3,11,19-trioxatetracyclo[19.3.1.1 5,9 .1 13,17 ]heptacosa-1(25),5,7,9(27),13,15, 17(26),21,23-nonaene-25,26,27-triyltris(oxyacetate), C 54 H 54 O 12 }, in a partial-cone conformation, which crystallizes with two molecules in the asymmetric unit. In this conformation, (I-CH 2 CO 2 Et) is adapted for selective complexation of the K + cation. We describe in this paper the synthesis and conformational behaviour of (I-CH 2 CO 2 Et) as determined by 1 H NMR spectroscopy and X-ray diffractometry

Double partial cone conformation for p-cumylcalix[6]arene·2.5 dimethylformamide

Abstract The crystal structure of p-cumylcalix[6]arene·2.5 dimethylformamide has revealed that the compound exists in the double partial cone conformation. The DMF molecules are bound to the calixarene via hydrogen bonds. The compound crystallizes in the triclinic space group P1 with a = 17.328(3), b = 17.981(3), c = 17.040(3) A, α = 116.56(2), β = 112.42(1), γ = 76.18(2)°, and Dc = 1.165 g cm−3 for Z = 2. Refinement based on 9418 observed reflections led to a final R value of 0.08.

NMR spectroscopic and X-ray crystallographic studies of calix[4]arene·Ag+complexes. Influence of bound Ag+on C2v–C2vinterconversion in cone-calix[4]arenes

The Ag+ complexes of conformationally immobilized tetra-O-propylcalix[4]arene with a cone or a partial-cone conformation (cone-2Prn or partial-cone-2Prn, respectively) have been successfully analysed by X-ray crystallography. In both complexes Ag+ was bound to the upper rim cavity, sandwiched by the two para carbons in the distal phenyl units. The findings provide clear evidence for π-base participation. In particular, the basic calix[4]arene skeleton in partial-cone-2Prn·Ag+ is almost the same as that in partial-cone-2Prnitself. This establishes that partial-cone-2R possesses two distal benzene rings ideally preorganized for Ag+-binding. 1H NMR spectroscopic studies for the Ag+ complexes in solution indicated that Ag+ is bound to the same site as that in the solid state. In conformationally mobile 2Me, which exists in solution in equilibrium between cone and partial-cone, Ag+ induced a shift of the equilibrium to partial-cone to form the partial-cone-2Me·Ag+complex. This is ascribed to the ideal preorganization in partial-cone-2R for the Ag+-binding. These results are of great significance for an understanding of π-base participation in the metal-binding events and have important implications on the cation–π interaction in biological systems.

Metal Ion Binding to Calixarenes: Pendent Arm Coordination Assisted by Self-Inclusion

The synthesis and room-temperature single-crystal X-ray structural characterization of 25,27- di(allyloxy)-5,17-di-t-butyl-26,28-dimethoxycalix[4]arene are recorded. Crystals are monoclinic, C2/c, a 29.089(5), b 10.742(2), c 26.218(8) Ǻ, β 110.09(2)°, Z = 8; the structure was refined to a residual of 0.065 for 4103 independent 'observed' [I > 3σ(I)] reflections. The flattened partial cone conformation of the molecule allows inclusion of one of the methoxy substituents in a way which could block inclusion of a metal ion capable of polyhapto aromatic coordination and which may therefore explain why solution n.m.r. measurements indicate that silver(I) binds to the pendent alkene groups.

Novel Fluorometric Sensing of Ammonium Ions by Pyrene Functionalized Homotrioxacalix[3]arenes

Abstract Pyrene functionalized homotrioxacalix[3]arenes selectively recognize primary ammonium ions detected by an intramolecular excimer fluorescence change of partial cone conformer. This is a novel sensing system for primary ammonium ions.

Synthetic strategies to inherently chiral calix[4]arenes with mixed ligating functionalities at the lower rim

The syntheses of 19 atropisomeric inherently chiral calix[4] arenes derived from syn-proximal (1,2)-bis[(2-pyridylmethyl)oxy]calix[4]arene 2 and mixed syn-distal (1,3)-[(2-pyridylmethyl)oxy] [(2-quinolylmethyl)oxy]calix[4]arene 6 are described. Treatment of 2 with 1 equiv of electrophile RX in DMF in the presence of Cs 2 CO 3 afforded racemic tri-O-alkylated cone conformers 3a-k (A α A α B α C α type), while with an excess of alkylating agent under analogous conditions the chiral tetra-O-alkylated partial cone conformers 4a-d (A α A α B α B β type) were formed. Similarly, exhaustive alkylation of 6 with either PicCl.HCl or QuinCl.HCl gave the chiral partial cone derivatives 7a,b (A α A α A α B β type), respectively. Further alkylation of 3i (R=benzyl) with PicCl.HCl and Cs 2 CO 3 provided partial cone derivative 7c (A α A α A β B α type), while with PrBr and NaH cone tetraether 8 (A α A α B α C α type) was obtained. Proton and carbon NMR spectral features of these compounds are discussed. Atropisomerism in tri-O-alkylated calix[4]arenes was demonstrated by dynamic NMR studies on the less encumbered allyl derivative 3a, which showed no hint for conformational inversion up to 375 K. 2D COSY spectra clearly show that in partial cone structures 4d and 7a-c the N-heteroaryl pendant group of the totated aryl moiety lies in, and effectively fills, the calix cavity produced by the remaining three aryl rings. The structure of the trisubstituted racemic calix[4]arene 3i has been determined by X-ray crystallography. The molecule adopts a distorted cone conformation with the two pendant pyridinyl groups in th syn-proximal arrangement on one side of the pendant benzyl moiety. There is an intramolecular O-H...O hydrogen bond between the phenolic oxygen OD and the proximal etheral oxygen OA (to which is bonded the benzyl residue) with O...O 2.85 A˙

Structure of the partial cone conformer of 25,26,27,28-tetrakis[(2-pyridylmethyl)oxy]calix[4]arene

The partial cone conformer of tetrakis[(2-pyridylmethyl)- oxy]pentacyclo[ 19.3.1.13'7.19'13.115,19]octacosa- 1 (25),- 3,5,7 (28),9,11,13 (27), 15,17,19(26),21,23-dodecaene, (I), adopts a conformation in which the pendant OCH2py group of the rotated aryl ring is oriented away from the calixarene cavity produced by the other three aryl rings, with its N atom exo to the calixarene cup. The orientation of the four aromatic rings is such that two rings are almost parallel to each other and the other two are at an angle of 42 ° . This conformation precludes any solvent molecule being enclathrated within the small molecular cavity.

Crystal structure of cyanocalix[4]arene methyl ether

The title compound has been prepared by the addition of bromocalix[4]arene methyl ether to CuCN in N-methylpyrrolidone. The crystals belong to the monoclinic space groupP21/n witha=13.591(3),b=24.778(5),c=11.057(3)A,β=93.58(2)°, andDc=1.09 g cm−3 forZ=4. Refinement based on 1118 observed reflections led to a finalR value of 0.085. The molecule exhibits the partial cone conformation.

Structure of 5,11,17,23-tetra-tert-butyl-25,27-dicyanomethoxy-26,28-dimethoxycalix[4]arene

β,β'-{5,11,17,23-Tetra-tert-butyl-26,28-dimethoxypentacyclo[19.3.1.1 3,7 .1 9,13 .1 15,19 ]octacosa-1(25),3,5,7(28),9,11,13(27),15,17,19(26),21,23-dodecaene-25,27-diyldioxy}diacetonitrile, C 50 H 62 N 2 O 4 , M r =755.1, monoclinic, C2/c, a=14.659 (1), b=16.591 (1), c=37.558 (5) A, β=90.38 (1) o , V=9134.19 A 3 , Z=8, D x =1.098 g cm -3 , λ(Mo Kα)=0.7107A, μ=0.64 cm -1 , F(000)=3264.0, T=293 K, wR=0.060 (w=1) for 4394 observed reflections with I>3σ(I). The x-ray structure shows that the compound adopts a partial-cone conformation in which the two anisole moieties are parallel to each other with the methoxy groups pointing outwards. The cyano groups are in anti positions

Calixarene Phosphorylation: Cation Control of Reaction Pathways

The hydroxide ion catalysed phosphorylation of p-t- butylcalix [4] arene by diethyl chlorophosphate under heterogeneous conditions shows a marked sensitivity to the nature of the phase transfer catalyst used. Thus, substitution of tetraethylammonium bromide for the tetrabutylammonium bromide prescribed for the synthesis of the calixarene tetraphosphate leads to a major reaction product becoming a bis (phosphate) in which the calixarene binds as a unidentate ligand to one phosphorus and as a bidentate ligand to the other. An X-ray crystal structure analysis on this new compound shows the calixarene to adopt a somewhat distorted 'cone' conformation with an unusual orientation of one of the t-butyl substituents into the cone cavity. It also reveals that a significant diastereoselectivity must operate in the formation reaction. The only other reaction product detected in this system appears to be the calixarene tetraphosphate in a partial cone conformation.

“Cone” - “Partial-cone” Isomerism in Tetramethoxycalix[4]arenes. Influence of Solvent Polarity and Metal Ions

It was found that the “cone” - “partial-cone” equilibrium in 25,26,27,28-tetramethoxycalix[4]arene derivatives is sensitively affected by the solvent polarity: the cone% increases with the increase in the solvent polarity. The novel finding was rationalized in terms of the difference in the dipole moment: cone conformers with four dipole moments orientating into the same direction are more polar than partial-cone conformers with one inverted phenyl unit and therefore are more stabilized in polar solvents. Alkali metal cations such as Li + and Na + strongly interact with four methoxy oxygens, resulting in the shift of the equilibrium to cone.

Conformational isomerism in and binding properties to alkali-metals and an ammonium salt of O-alkylated homooxacalix[3]arenes.

7,15,23-Tri- tert-butyl-25,26,27-trihydroxy-2,3,10,11,18,19-hexahomo-3,11,19-trioxacalix[3]arene ( 1H 3) was tri- O-alkylated with alkyl halides (RX: R=Me, Et, n-Pr, and n-Bu) in the presence of various bases and the products ( 1R 3) were analyzed by HPLC and 1H NMR spectroscopy. It was found that (i) ring inversion which occurs through the oxygen-through-the-annulus rotation is allowed for 1Me 3, 1Et 3, and 1Pr 3 whereas it is inhibited for 1Bu 3, (ii) the cone/partial-cone equilibrium in 1Et 3 and 1Pr 3 is predominantly inclined to partial-cone, indicating the thermodynamic stability of partial-cone conformers, and (iii) in the product distribution of 1Bu 3 partial-cone is yielded in preference for cone, indicating the kinetic preference for partial-cone. From the analysis of the reaction intermediates the possible reaction routes to cone- and partial-cone- 1Bu 3 are discussed. 1R 3 showed the selectivity toward K + among alkali metal cations and the cone conformers had the extractability (Ex%) higher than the partial-cone conformers. Cone- 1R 3 showed the high affinity for BuNH 3 + because of (averaged) C 3 symmetry common to both cone- 1R 3 host and BuNH 3 + guest.

Double partial cone conformation for Na8{calix[6]arene sulfonate}.cntdot.20.5H2O and its parent acid

The chemistry of calixarenes has recently become a very active area of endeavor. Of the numerous stimulating findings to appear thus far in the literature, one of the most intriguing concerns the discovery of certain uranophiles by Shinkai. It was reported that calix[5]arene sulfonate, calix[6]arene sulfonate, and the two corresponding derivatives substituted at the base by carboxymethoxy groups, 1 with R{prime} = CH{sub 2}COOH, exhibited stability constants for the uranyl ion of K = 10{sup 18.4-19.2}. Indeed, in competition experiments these calixarenes showed selectivity factors of 10{sup 12-17} for uranyl over the Ni{sup 2+}, Zn{sup 2+}, and Cu{sup 2+} ions. This selectivity was attributed to a moderately rigid calix[6]arene structure which was preorganized to match the rather unusual pseudoplanar hexacoordination needs of the UO{sub 2}{sup 2+} ion. However, on the basis of this study this premise appears untenable. Considering the importance of the above mentioned findings, the structural chemistry of derivatives of calix[6]arene has been slow to develop. In the available selection it is difficult to find general conformational features, apart from the elliptical cone conformation exhibited by the parent p-tert-butycalix[6]arene. Since our group has found a rich and often surprising inclusion chemistry for calix[4]arene sulfonates, we decided to investigatemore » the structure of calix[6]arene sulfonate and its alkali metal salts. 28 refs., 1 fig.« less

A conformational study of the calixspherand and its complexes with alkalimetal cations

The calixpherand 2 forms kinetically very stable complexes with alkalimetal cations. This molecule is not completely preorganized for binding of a cation, as is evidenced from the results of NOESY spectroscopy and X-ray diffraction measurements. Both in CDCl3 solution and in the solid state the free ligand adopts a cone conformation, whereas the Na+ complex adopts a flattened partial cone conformation. Molecular-mechanics calculations with different programs give rather biased results. Calculations with QUANTA(the all atom CHARMM-force field) correctly predict the conformation of the free ligand but not of the complexes, whereas with MACROMODEL(the united atom AMBER-force field) the experimentally observed conformation had the lowest energy only for the Na+ complex. The calculated geometries of the experimentally found conformations of the free ligand and the Na+ complex agree well with the X-ray structures, especially for the structures that were obtained with QUANTA. A comparison of the calculated structures of the Na+, K+ and Rb+ complexes showed that larger cations force the terphenyl bridge to bend away, thereby opening up the cage of the ligand and making the cation more accessible to solvent molecules. This might explain the considerably lower kinetic and thermodynamic stability of the Rb+ complex compared with those of the Na+ and K+ complexes.

Stereoselective synthesis and optical resolution of chiral calix[4]arenes with mixed ligating functionalities

Exhaustive alkylation of syn-proximal bis[(2-pyridylmethyl)oxy]calix[4]arene 1 with t-butyl bromoacetate or 2-(chloromethyl)quinoline hydrochloride in the presence of Cs 2CO 3 affords selectively a new type of inherently chiral calix[4]arenes 2a,b in the partial cone conformation. (±) 2b has been resolved into its optical antipodes by an HPLC method.

Syn-1,2-dialkylated calix[4]arenes : general intermediates in the NaH/DMF tetraalkylation of calix[4]arenes

In DMF or acetonitrile with NaH as a base at room temperature the tetraalkylation of calix[4]arenes 1a and 1b proceeds via the syn-1,2-disubstituted products to the tetraalkylated calix[4]arenes in the cone conformation. With KH as a base the tetraalkylated calix[4]arenes are predominantly formed in the partial cone conformation, and the reaction proceeds via both the syn-1,3-di and the syn-1,2-disubstituted products. Also the solvent influences the pathway via which tetraalkylation takes place. The syn-1,2-disubstituted calix[4]arenes 4– 6 can be isolated in 15–55 % from the NaH/DMF or MeCN reactions when only 2.2 equiv of the electrophile are used.

Thiocalix[4] arenes. I. Synthesis and structure of ethylthiocalix[4]arene methyl ether and the related structure of bromocalix[4]arene methyl ether

Bromocalix[4]arene methyl ether serves as a precursor in the synthesis of the title thiocalixarene via the reagent CuSEt. Ethylthiocalix[4]arene methyl ether crystallizes in the monoclinic space groupP21/c witha = 20.577(9),b, = 10.722(5),c = 20.315(9) A, β = 120.46(4)°, andDc = 1.24 g cm−3 forZ = 4. Refinement based on 1441 observed reflections led toR = 0.080. The configuration of the calixarene lies between the partial cone and the 1,3-altemate conformations. Bromocalix[4]arene methyl ether crystallizes in the triclinic space groupPI witha = 12.283(7),b = 17.658(9),c = 18.118(6) A, α = 90.25(6), β = 105.95(4), γ = 105.11(6)°, andDc = 1.68 g cm−3 forZ = 4. Refinement based on 3028 observed reflections led toR = 0.083. The unit cell also contains four CHCl3 molecules which exist pairwise enclathrated by six calixarenes. The partial cone conformation of the bromocalixarene is identical to that of ethylthiocalix[4]arene methyl ether.

Calix[4]arenes bridged at the lower rim

Calix[41 arenes, in which two opposite p-positions are linked by an aliphatic chain, and their derivatives show transport or complexation properties strongly dependent on the length of this chain. Bicyclo-calix[4]arenes, a special case of 1,3-bridged calix[41 arenes, and annelated calix[41 arenes, a special case of 1 ,&bridged calix [4] arenes, are also described. Although the preferred conformation of calix[4]arenes is the coneconformation due to its stabilization by a cyclic array of hydrogen bonds between the phenolic hydroxyl goups, these molecules are flexible, with a cone to cone inversion rate of about 150 8-1 for a calix[glarene at 47OC (ref. 1). The cone (or any other) conformation may be fixed by derivatisation of the phenolic oxygens. Another possibility is, to connect two p-positions of opposite (1) or adjacent (3) phenolic units by a suitable bridge. Although partial cone or alternate conformations still are possible in these compounds, the complete ring inversion is entirely prevented by the bridge. Compounds of type 1 with (CH2 In -bridges are available by reaction of suitable diphenols with bisbromomethylated phenols in dioxane in the presence of Tic14 (ref. 2).

Dimer and trimer calix[4]arenes containing multiple metallocene redox-active centres. Single-crystal X-ray structure of a bis(ferrocene)-bis(p-t-butylcalix[4]-arene) hydrophobia host molecule

The condensation of 1,1′-bis(chlorocarbonyl)ferrocene (1) and 1,1′-bis(chlorocarbonyl)ruthenocene (2) with p-t-butylcalix[4]arene gave the respective new redox-active metallocene–calix[4]arene dimers (3) and (4). An X-ray diffraction study of (3) shows the two calix[4]arenes to be in cone conformations with a metallocene metal atom transannular Fe ⋯ Fe separation of 5.9 A. The reaction of 1,1′-bis(chlorocarbonyl)cobaltocenium chloride (5) and p-t-butylcalix[4]arene gave a cobaltocenium–bis(p-t-butylcalix[4]arene) dimer (6). A ferrocene–calix[4]arene trimer (7) was isolated from the reaction of (1) and calix[4]arene. Solution variable-temperature 1H n.m.r. studies show (3) and (4) to be conformationally mobile with respective low-temperature spectra consistent with either partial cone conformations or cis orientation of respective metallocene carbonyl ester moieties. Cyclic voltammetric and coulometric studies in acetonitrile reveal that compound (3) undergoes a reversible two-electron oxidation at +1.24V (versus saturated calomel electrode), suggesting the two respective ferrocene moieties are oxidised in one step. Proton n.m.r. complexation studies showed (3) to be incapable of forming a solution host–guest complex with t-butylamine.

Conformational and complexational characteristics of calixarenes

Abstract