An efficient synthesis and structural aspects of hexakis(arylseleno)benzenes and hexakis(arylselenomethyl)benzenes

An efficient synthesis and structural aspects of a novel class of selenium bearing hexa-hosts by the reaction of hexafluorobenzene or hexakis(bromomethyl) benzene with RSe⁻ ions is demonstrated. However, under identical reaction conditions, our attempts to prepare tellurium analogues by the reaction of RTe⁻ (R = Ph or p-CH₃C₆H₄-) with hexafluorobenzene or hexakis(bromomethyl)benzene to obtain (RTe)₆C₆ and (RTeCH₂)₆C₆ proved to be difficult.     

Sterically encumbered hexakis(alkylseleno)benzenes: conformational behavior of hexakis(iso-propylselenomethyl)benzene toward Hg ions on selective recognition

An efficient synthesis and structural aspects of a novel class of hexakis(alkylseleno)benzenes [(RSeCH₂)₆C₆] (R = Me, ⁱPr, ⁿBu, ^sBu, ^tBu, ⁿPn, ⁿHx, ⁿOct, 1-methylnaphthalene) by the reaction of hexakis(bromomethyl)benzene with RSe⁻ ions is demonstrated. Preliminary data on ion-sensing properties reveal that these species may act as selective ionophores for Hg²⁺ ions.     

Synthesis and self-association, absorption, and fluorescence properties of differentially functionalized hexakis(p-substituted-phenylethynyl)benzenes

The dual Sonogashira coupling reactions of 1,3,5-tribromo-2,4,6-triiodobenzene with p-X-phenylacetylene followed by another p-Y-phenylacetylene (X, Y = OSiMe(2)Bu-t or CO(2)Et) produced a series of differentially functionalized hexakis(p-substituted-phenylethynyl)benzenes with D(3)(h)() symmetry (3h: 1,3,5-X-2,4,6-Y) and C(2)(v)() symmetry (3g,i: 1,2,3,5-X-4,6-Y; 3f,j: 1-X-2,3,4,5,6-Y). In a similar manner, 1,3,5-tris(p-X-phenylethynyl)-2,4,6-tris(p-Y-phenylethynyl)benzenes and 1,2,3,5-tetrakis(p-X-phenylethynyl)-4,6-bis(p-Y-phenylethynyl)benzenes (3l: X = OSiMe(2)Bu-t, Y = NO(2); 3m,n: X = N(n-octyl)(2), Y = NO(2); 3o,p: X = N(n-octyl)(2), Y = CH(OCH(2)CH(2)O); 3q,r: X = N(n-octyl)(2), Y = CHO; 3s,t: X = N(n-octyl)(2), Y = CH=C(CN)(2)) were prepared. Compounds 3 with electron-withdrawing groups self-aggregated by a pi-pi stacking interaction and solvophobic effect. In the absorption and fluorescence spectra of 3, lambda(max)(abs) and lambda(max)(em) showed red shifts as the donor-acceptor dipole at the end functional groups of the para position was increased. In the absorption spectra, lambda(max)(abs) showed red shifts upon increasing the number of combination of electron-donating and -withdrawing groups on the diagonal line in a molecule, whereas lambda(max)(em) in the fluorescence spectra exhibited red shifts upon decreasing the molecular symmetry.     

Complex formation of hexakis(2,3,6-tri-O-methyl)-α-cyclodextrin with substituted benzenes in aqueous solution

The complex formation of hexakis (2,3,6-tri-O-methyl)--cyclodextrin with substituted benzenes has been investigated by circular dichroism (CD) spectroscopy. The sign and shape of the CD spectra markedly differ from the spectra of corresponding -cyclodextrin complexes because of the distorted conformation of the host molecule and/or the difference in the geometry of the host-guest interaction. Enthalpy and entropy changes of the complex formation are determined by using the CD band intensities measured at various temperatures and host concentrations. Negative values of H and S indicate that the hydrophobic interaction is not the major driving force for the complex formation. The guest molecule is suggested to be tightly bound within the host cavity through the induced-fit conformational change of the host molecule.     

Structure of the liquid crystalline state in hexakis (4-(4'-alkyloxy)biphenoxy)cyclotriphosphazenes

X-ray measurements on hexakis(4-(4'-alkyloxy)biphenoxy)cyclotriphosphazenes [PN-(OC₆H₄C₆H₄OC_nH_{2n + 1})₂]₃ (HACP, n = 7-9), confirm the previous mesophase identification. The apparent molecular length measured in the mesophase compares to twice the length of an alkyloxybiphenyl side group. Specific features are added to the usual features of the nematic and smectic diffraction patterns which show that the molecular arrays in directions parallel and perpendicular to the director both reflect the peculiar shape of the cyclotriphosphazenes.     

Preparation of SF5 aromatics by vicarious nucleophilic substitution reactions of nitro(pentafluorosulfanyl)benzenes with carbanions

Vicarious nucleophilic substitutions (VNS) of hydrogen in 1-nitro-4-(pentafluorosulfanyl)benzene with carbanions provide 2-substituted 1-nitro-4-(pentafluorosulfanyl)benzenes in good to high yields. VNS of 1-nitro-3-(pentafluorosulfanyl)benzene gives a mixture of 6- and 4-substituted 1-nitro-3-(pentafluorosulfanyl)benzenes in 85:15 to >98:2 ratio and good to high yields. In basic media, the VNS reactions lead to the formation of carbanions that can be alkylated by alkyl halides affording the corresponding alkylated products in moderate yields. Transformation of primary products to substituted (pentafluorosulfanyl)anilines and 3- or 4-substituted (pentafluorosulfanyl)benzenes is also described.     

Potassium Cryptate of a Macrobicyclic Ligand Featuring a Reducible hexakis(phenylthio)benzene electron-acceptor site

The synthesis and structural characterization of the macrobicyclic ligand 1 containing a reducible hexakis-(phenylthio)benzene electron-acceptor site is described. It is based on the condensation of the tetraoxa-diazamacrocycle 3 with a suitably functionalized derivative 4 of hexakis(phenylthio)benzene. Complexation of a potassium cation by 1 gives the corresponding cryptate 2 , with a stability constant of ca. 4000 M ^?1 as determined by ¹H-NMR titration in CD₃CN. The reduction potential of the hexakis(phenylthio)benzene electron-acceptor site in 2 is shifted by 170 mV towards more positive values with respect to that in 1 by complexation of potassium.     

Catalytic [2+2+2] and thermal [4+2] cycloaddition of 1,2-bis(arylpropiolyl)benzenes

We have determined that a cationic rhodium(I)/Segphos complex catalyzes an enantio- and diastereoselective intermolecular [2+2+2] cycloaddition of 1,2-bis(arylpropiolyl)benzenes with various monoalkynes at room temperature to give axially chiral 1,4-teraryls possessing an anthraquinone structure in good yields with good enantio- and diastereoselectivities. We have also determined that a thermal intramolecular [4+2] cycloaddition of 1,2-bis(arylpropiolyl)benzenes proceeds at 60 degrees C to give aryl-substituted naphthacenediones in moderate to good yields.     

Diammonium hexakis(thiocyanato‐κN)rhenate(IV) dimethyl sulfone tetrasolvate

The title compound, (NH₄)₂[Re(NCS)₆]·4C₂H₆O₂S, was obtained by solvothermal synthesis as part of a project on rhenium thiocyanate catalysts and starting materials for further aggregation to molecular magnets. The compound is the ammonium salt of octahedral hexakis(thiocyanato‐κN)rhenate(IV) anions, which lie on centres of inversion. The dimethyl sulfone solvent molecules are involved in R₄²(8) and D N—H...O hydrogen‐bonded motifs. N—H...S and S...S short contacts are also present. Hydrogen‐bonded ammonium–dimethyl sulfone layers alternate with layers formed by the complex anion (with S...S short contacts) parallel to (100).     

(1+1) or (2+2) Coupling for bis(tosyloxyethoxy)benzenes with calix[4]arene and thiacalix[4]arene

As bifunctional reagents, bis(tosyloxyethoxy)benzenes can react with p-tert-butylcalix[4]arene or p-tert-butylthiacalix[4]arene to afford intramolecularly bridged (1+1) or intermolecularly bridged (2+2) products. It was found that the bridging pattern strongly depended on the structure of bis(tosyloxyethoxy)benzene and the kind of calixarene. For the ortho-isomer of bis(tosyloxyethoxy)benzene, intramolecularly bridged calix[4]arene and thiacalix[4]arene were the main products. For the para-isomer, the bridging reaction was in a (2+2) fashion. As for the meta-isomer, double thiacalix[4]arene and intramolecularly bridged calix[4]crown were synthesized.     

Two‐Photon Absorption Properties of Dehydrobenzo[12]annulenes and Hexakis(phenylethynyl)benzenes: Effect of Edge‐Linkage

Two‐photon absorption (TPA) properties of two trefoil‐shaped compounds with different edge linkages—tris(hexadehydrotribenzo[12]annulene) and tris(tetradehydrotribenzo[12]annulene)—and three asterisk‐shaped compounds having no edge‐linkage—hexakis(phenylethynyl)benzenes—are investigated experimentally by the open‐aperture Z‐scan and TPA‐induced fluorescence methods with wavelength tuneable femtosecond pulses. The compound with ethynylene edge‐linkage exhibits the most intense TPA (the maximal TPA cross section is 1300±170 GM at 572 nm where 1 GM=10^?50 cm⁴ s molecule^?1 photon^?1). The TPA activity of the compounds is primarily explained in terms of the planarity of the molecules in relation with the type of edge‐linkage.     

Solvent-induced polymorphism of three-dimensional hydrogen-bonded networks of hexakis(4-carbamoylphenyl)benzene

The crystal structures for three types of three-dimensional (3-D) hydrogen-bonded networks of hexakis(4-carbamoylphenyl)benzene (1), the network morphologies of which depend greatly on crystallization conditions, have been determined. When this compound is crystallized from hot DMSO, the resulting crystals, 1.12DMSO (orthorhombic, Pca2(1)), showed a 3-D hydrogen-bonded porous network (type A) via 1-D catemer chains as a hydrogen-bonding motif of six primary amide groups. The type A network creates chambers surrounded by six molecules of 1 and channels along the c axis to give the highest porosity among the network polymorphs of 1 investigated here. Crystallization from a boiling mixture of n-PrOH and water gave 1.6n-PrOH (monoclinic, P2(1)/c), which exhibits another type of 3-D hydrogen-bonded porous network (type B) via cyclic dimers as another hydrogen-bonding motif of six primary amide groups. The type B network leads to triangle-like channels along the a axis having a cross section of ca. 9.2 x 9.7 x 9.7 A (including van der Waals radii). The crystal structure of 1.H(2)O (monoclinic, P2(1)/c), which was produced under hydrothermal conditions, showed a nonporous 3-D hydrogen-bonded network chain of amide groups (type C) composed of a mixed hydrogen bonding motif of helical catemer chains/cyclic dimer/catemer. Solvent-induced topological isomerism of these 3-D hydrogen-bonded networks of 1 arises from (i) the guest inclusion ability based on a radially functionalized hexagonal structure of 1, (ii) the correlation between the hydrogen bond donor ability of the syn and anti protons of the primary amide group in host 1 and the hydrogen bond acceptor ability of the oxygen atoms of 1 and guest solvents, and (iii) the polarity of the bulk crystallization solvents.     

Electrochemical Oxidation of Bis(methylthio)benzenes

The bis(methylthio)benzenes 3a – 3c are oxidized to the methylsulfinyl-methylthiobenzenes 4a – 4c on a Pt-anode in good yields.     

Synthesis of isomeric 1,3- and 1,4-bis[3(4)-nitrofuroxan-4(3)-yl]nitrobenzenes by nitration of the corresponding isomeric 1,3- and 1,4-bis[3(4)-nitrofuroxan-4(3)-yl]benzenes

Isomeric 1,3- and 1,4-bis[3(4)-nitrofuroxan-4(3)-yl]nitro(dinitro)benzenes were synthe-sized in high yields by nitration of the corresponding 1,3- and 1,4-bis[3(4)-nitrofuroxan-4(3)-yl]benzenes with a mixture of 100% nitric acid and concentrated sulfuric acid. The influence of 3- and 4-nitrofuroxanyl fragments on the regioselectivity of the nitration was revealed. The structure of 1,3-bis(4-nitrofuroxan-3-yl)-4-nitrobenzene was confirmed by X-ray diffraction analysis. 1,3- and 1,4-Bis(3-nitrofuroxan-4-yl)nitrobenzenes underwent thermal isomerization to more thermodynamically favorable 1,3- and 1,4-bis(4-nitrofuroxan-3-yl)nitrobenzenes.     

Acid-catalyzed reaction of 4-methyl-1,2,4-triazoline-3,5-dione (MeTAD) with substituted benzenes

The reaction of 4-methyl-1,2,4-triazoline-3,5-dione (MeTAD) with substituted benzenes under the influence of trifluoroacetic acid catalysis was investigated. Generally, good-to-high yields of 1-arylurazoles resulting from aromatic substitution were obtained. Successful reaction required moderately electron-rich aromatics with proper substitution patterns. The reaction was tolerant of functionality on the aromatic ring.     

Gearing of molecular swirls: columnar packing of nematogenic hexakis(4-alkoxyphenylethynyl)benzene derivatives

Through molecular design and straightforward synthesis, incorporating an additional alkoxy chain onto various numbers of peripheral phenyls in nematogenic hexakis(4-alkoxyphenylethynyl)benzene was achieved to generate columnar phases with significantly expanded temperature ranges. For the compound with two decyloxy chains on every peripheral phenyl, scanning tunnelling microscopic studies indicate the molecule adopts a preferred molecular-swirl geometry by restricting the conformational arrangement of the alkoxy side chains. Cooperative packing of the molecular swirls by a lock-in mechanism among columns results in a stable helical column packing evidenced by powder X-ray diffraction.     

A new mixed acetal-type substitution pattern for alpha-cyclodextrin. Preparation of hexakis (3-O-benzyl)- alpha-cyclodextrin

alpha-CD was converted into hexakis[2,6-di-O-(methoxydimethyl)methyl]-alpha-CD by a proton-catalyzed reaction with 2-methoxypropene. Subsequent benzylation under Brimacombe conditions resulted in the fully protected compound, from which the acid-sensitive acetal groups were removed to obtain hexakis(3-O-benzyl)-alpha-cyclodextrin. The structure of all of the compounds synthesized was confirmed by 13C J-ECHO, COSY, HETCOR and HMBC NMR measurements.     

Structure-property relationships of donor/acceptor-functionalized tetrakis(phenylethynyl)benzenes and bis(dehydrobenzoannuleno)benzenes

A series of tetrakis(phenylethynyl)benzenes and bis(dehydrobenzoannuleno)benzenes have been synthesized containing tetra-substitutions of neutral, donor, and mixed donor/acceptor groups. To ascertain the importance of substitutional and structural differences of the phenylacetylenes, the optical absorption and emission properties of each series were examined. Conjugation effectiveness, electron density, planarity, and geometry of charge-transfer pathways were found to have a pronounced effect on the overall optical and material properties. Considerable self-association behavior due to face-to-face stacking in solution was observed for donor/acceptor-functionalized macrocycles and was quantified by concentration-dependent (1)H NMR measurements. A solvent-dependent polymerization of one macrocycle regioisomer was observed and characterized. To provide further insight into the energy levels and electronic transitions present, computational studies of each system were performed.     

Multilayered nanofibers from stacks of single-molecular thick nanosheets of hexakis(alkoxy)triphenylenes

Symmetrically substituted hexakis(alkoxy)triphenylene (HAT) derivatives were assembled into single molecular thick 2D nanosheets, which stacked further to give multilayered nanofibers through a convenient solution process. Detailed information on molecular arrangement was unraveled by various imaging techniques and diffraction studies.     

Synthesis and characterization of thermally stable and flame retardant hexakis(4-aminophenoxy)cyclotriphosphazene-based polyimide matrices

A new approach to the preparation of hexakis(4-aminophenoxy)cyclotriphosphazene (HACTP) based polyimide (PI) matrices is proposed, for improved thermal and flame retardant properties. HACTP was synthesized with good yield. The structure of HACTP was confirmed by various characterization techniques, such as FTIR, NMR, and mass Spectroscopy. Polyimide matrices were prepared by thermal imidization process using HACTP and dianhydrides using N-methyl pyrrolidone as a solvent. The successful formation of HACTP-based polyimide matrices was confirmed by the FTIR. Thermal properties of the PI were analyzed using DSC and TGA techniques. Data obtained from the thermal studies indicate that the HACTP-based PI possesses better thermal and flame retardant properties.