An efficient synthesis of hexa-substituted benzenes and the discovery of a novel host conformation for hexakis (β-naphthylthio) benzene

Charge Transport through Single-Molecule Junctions with σ-Delocalized Systems

Single-molecule junctions, formed by a single molecule bridging a gap between two metal electrodes, are attracting attention as basic models of ultrasmall electronic devices. Although charge transport through π-conjugated molecules with π-delocalized system has been widely studied for a number of molecular junctions, there has been almost no research on charge transport through molecular junctions with a σ-delocalized orbital system. Compounds with hexa-selenium-substituted benzene form a σ-delocalized orbital system on the periphery of the benzene ring. In this study, we fabricated single-molecule junctions with the σ-delocalized orbital systems arising from lone-pair interactions of selenium atoms and clarified their electronic properties using the break-junction method. The single-molecule junctions with the σ-orbital systems show efficient charge transport properties and can be one of the alternatives to those with conventional π-orbital systems as minute electronic conductors.

"The Sulfur Dance" Around Arenes and Heteroarenes - the Reversible Nature of Nucleophilic Aromatic Substitutions

We disclose the features of a category of reversible nucleophilic aromatic substitutions in view of their significance and generality in dynamic aromatic chemistry. Exchange of sulfur components surrounding arenes and heteroarenes may occur at 25 °C, in a process that one may call a "sulfur dance". These SN Ar systems present their own features, apart from common reversible reactions utilized in dynamic covalent chemistry (DCC). By varying conditions, covalent dynamics may operate to provide libraries of thiaarenes with some selectivity, or conversion of a hexa(thio)benzene asterisk into another one. The reversible nature of SN Ar is confirmed by three methods: a convergence of the products distribution in reversible SN Ar systems, a related product redistribution between two per(thio)benzenes by using a thiolate promoter, and from kinetic/thermodynamic data. A four-component dynamic covalent system further illustrates the thermodynamically-driven formation of a thiacalix[2]arene[2]pyrimidine by sulfur component exchanges. This work stimulates the implementation of reversible SN Ar in aromatic chemistry and in DCC.

Access to NHC-Boryl Mono- and Bis-Selenide and Utility as Mild Selenium Transfer Reagent Including to the C-F Bond

Reactions of 5-SIDipp ⋅ BH3 (5-SIDipp=1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene) (1) with diphenyldiselenide provide access to 5-SIDipp-boryl mono- (5-SIDipp ⋅ BH2 SePh) (2) and bis-selenide (5-SIDipp ⋅ BH(SePh)2 ) (3). The facile cleavage of the B-Se bond makes 2 a neutral source of selenium nucleophiles in substitutions reactions with benzyl bromides, and provide access to the corresponding selenoethers. The direct transformations of one of the C(sp2 )-F bonds of C5 F5 N and C6 F5 CF3 to C-Se bonds have also been achieved by the use of 2 without employing transition-metal catalysts. While it was previously established that C6 F6 could undergo complete defluoroselenation under harsh conditions, we successfully achieved partial defluorination of C6 F6 by employing 2 as a mild selenide transfer reagent. During the formation of C-Se bonds through the cleavage of C-F bonds, the potential by-product NHC ⋅ BH2 F undergoes ring expansion of the NHC, leading to the formation of the six-membered diaazafluoroborinane (7).

Janus triple tripods build up a microporous manifold for HgCl2 and I2 uptake

Three tripods for a versatile molecular scaffold: combining the Janus core for supramolecular recognition and the planar carboxyl tripod for framework construction enables metal uptake and iodine removal applications.

Accessing libraries of bifunctional block copolymers using two distinct pentafluorophenyl moieties

The suitability of pentafluorophenyl (PFP) esters and PFP alkyl moieties for orthogonal dual functionalization of block copolymer segments is evaluated. While amidation followed by para-fluoro–thiol substitution is a viable reaction sequence, thiol-based substitution can occur on PFP esters at a high rate, thereby hampering the viability of the reverse sequence.

1,2,4,5-Tetrakis(phenylsulfonyl)benzene: a novel quadruped host with D2 symmetry having ordered sulfolane and cycloheptanone guests

The title tetrasulfone 1, in common with higher members of the multi-armed aromatic hosts, forms host-guest complexes with polar guest molecules. In the sulfolane and cycloheptanone complexes the host molecule possesses an abab conformation with exact C(2,) and approximate D(2) symmetry with deviations owing to crystal packing forces. The conformation of the well-ordered cycloheptanone molecule, which normally undergoes facile pseudorotation, is unambiguously defined in the voids of the crystalline inclusion compound.

Synthesis of self-organizing mesogenic materials containing a sulfur-based five-membered heterocyclic core

The majority of low molar mass calamitic mesogenic systems in the literature contain linear cores based on the 1,4-disubstituted phenyl ring. Heterocyclic cores such as thiophene impart unique physical properties as their slightly bent structure leads to features including a reduced packing ability (generally giving rise to lower melting points than their phenyl counterparts), a medium to strong lateral dipole, high anisotropy of the polarizability, low viscosity etc. This critical review describes the most recent synthetic methodology that has been used to prepare thiophene, 1,3-thiazole, and 1,3,4-thiadiazole-based mesogenic materials.

Persulfurated Aromatic Compounds

Persulfurated arenes have been known for about 50 years but they were underexploited in chemistry in spite of facile, mild, and high-yielding syntheses. Their properties (redox potentials, UV/Vis absorption, conductivity, nonlinear optical properties, etc.) are mainly due to the aromaticity of the ring with sp2-hybridized carbon atoms and to the electronic contribution from numerous divalent sulfur ligands, which also stabilize negative or positive charges. The characteristic conformational patterns of the sulfur ligands often facilitate preorganization in supramolecular assemblies, with or without thiophilic metal cations, for designing redox sensors, ion-selective membranes, clathrates, organic conductors, nonlinear optical materials, liquid crystals, coordination polymers, and bioinorganic systems. A new class of supramolecules with various molecular shapes such as asterisks, chains, wheels, and windmills were reported.

Three-Dimensional Nets from Star-Shaped Hexakis(arylthio)triphenylene Molecules and Silver(I) Salts

This article reports a number of functional 3D networks based on the coordination bonds between the silver(I) ion and polycyclic aromatic 2,3,6,7,10,11-hexakis(organylthio)triphenylene (HRTT) molecules. First, 2,3,6,7,10,11-hexakis(phenylthio)triphenylene (HPhTT) chelates with AgBF4 (or AgTf, where Tf is triflate) in the presence of hexafluorobenzene to form a 3D network (composition, HPhTT x AgBF4; space group, I4), where each Ag(I) atom is bonded to three HPhTT molecules and acts as a three-connected node that interconnects the trigonal HPhTT ligands. In addition to the relatively rare 8(2) x 10-a topology, the network features distinct channel-like domains that incorporate various solvent molecules (e.g., acetone and tetrahydrofuran). The solvent molecules can be evacuated to produce a stable and crystalline apohost network, in which the solvent-accessible fraction of the cell volume is calculated to be about 16%. Second, chelation of 2,3,6,7,10,11-hexakis(4-methoxyphenylthio)triphenylene (HMOPhTT) and AgSbF6 in a 1:1 ratio results in a 3D network featuring a similar 8(2) x 10-a topology and Ag(I) coordination environment. However, the crystallographic symmetry (space group Cc) is lowered, and the feature of porosity is much less distinct. The 3D networks show strong room-temperature fluorescence bands with lambda(F,max) = 450 nm, due to the pi-electron fragment of the triphenylene group.

Fluorescent Coordination Networks of 2,3,6,7,10,11-Hexakis(phenylthio)triphenylene and Silver(I) Triflate

The polycyclic aromatic ligand 2,3,6,7,10,11-hexakis(phenylthio)triphenylene (HPhTT) coordinates with AgTf (Tf = trifluoromethylsulfonate) to form 1D networks with various solvent molecules included. In particular, the crystal structures and photoluminescent properties of compound 1 (formula = 2HPhTT.3AgTf.3toluene) and compound 2 (formula = 2HPhTT.3AgTf.2THF) are described. Both 1 and 2 feature similar network connectivity as well as similar local coordination environments around the silver(I) atoms. The organizations of the guest molecules in the two structures are, however, quite different: In 1, the toluene molecules are enclathrated in isolated cavities by the host network; in 2, the THF molecules are confined in continuous 1D channels. Because of the large aromatic system of the triphenylene moiety, strong fluorescent bands (room temperature) are observed for HPhTT, 1 and 2, with lambda(F,max) = 447 nm for HPhTT and lambda(F,max) = 440 nm for both 1 and 2.

Polyvalent Interactions in Unnatural Recognition Processes

The synthesis of two cluster compounds, one containing six secondary dialkylammonium ion centers and the other possessing six benzo-m-phenylene[25]crown-8 (BMP25C8) macrocycles, both appended to hexakis(thiophenyl)benzene cores, is described. The binding of these clusters with complementary mono- and divalent ligands is investigated with NMR spectroscopy to probe polyvalency in these unnatural recognition systems. The ability of the two different families of clusters to bind complementary monovalent ligands is compared with that of the monovalent receptor pair, namely the dibenzylammonium ion and BMP25C8. This comparison is made possible by determining an average association constant (K(AVE)) for the binding of each recognition site on the cluster with the corresponding monovalent ligand. We have found that the clustering of recognition sites together in one molecule is detrimental to their individual abilities to bind monovalent ligands. In the case of the polyvalent interaction between the hexakisBMP25C8 cluster and divalent dialkylammonium ions, an association constant, K(POLY), was calculated from the value of K(AVE) determined for the complexation of the individual component recognition sites. This polyvalent interaction is significantly stronger than that associated with the averaged monovalent interactions.

Synthesis and properties of water-soluble asterisk molecules

An asterisk is comprised of six semirigid arms projecting from a benzene nucleus. In the case at hand, asterisks were synthesized with one, two, or three aromatic rings (connected by sulfur atoms) in each of the six arms. A phosphomonoester at the termini of each arm solubilized the asterisks in water. The colloidal properties of these amphiphilic molecules were investigated by UV-vis and fluorescence spectroscopy, calorimetry, light scattering, surface tensiometry, and pulse-gradient spin-echo NMR. Solubility, solubilization, metal binding, and micelle "seeding" experiments were also carried out. Chain-conformation and supramolecular assembly into remarkable molecular "scrolls" were investigated by X-ray analysis and electron microscopy, respectively. One of the more interesting properties of the asterisks is that they remain monomeric in water despite having as many as 19 hydrophobic aromatic rings exposed to the water. The reasons for this behavior, and the possibility of exploiting it for constructing enzyme models free from aggregation equilibria, are discussed.