W Tungsten

We have previously reported that the trimeric Zn²⁺–cyclen complex (tris(Zn²⁺–cyclen), [Zn₃L¹]⁶⁺) and the trianion of trithiocyanuric acid (TCA³⁻) assembled in a 4:4 ratio to form a cuboctahedral supramolecular cage, [(Zn₃L¹)₄(TCA³⁻)₄]¹²⁺ (hereafter referred to as a Zn–cage), in neutral aqueous solution (cyclen=1,4,7,10-tetraazacyclododecane). Herein, we examined the molecular recognition of C₁–C₁₂ hydrocarbons (C_nH_(2n+2) (n≈1–12)), cyclopentane, cyclododecane, cis-decalin, and trans-decalin by the Zn–cage under normal atmospheric pressure. This cage complex was also able to encapsulate guest molecules that had larger volumes than that of the inner cavity of the Zn–cage, thereby suggesting that the inner shape of the Zn–cage was flexible. Computational simulations of Zn–cage–guest complexes provided support for this conclusion. Moreover, the solvent-accessible surface areas (SASA) of the Zn–cage host, guest molecules, and the Zn–cage-guest complexes were calculated and the data were used to explain the order of stability determined by the guest-replacement experiments. The storage of volatile molecules in aqueous solution by the Zn–cage is also discussed.

Be our guest: Molecular recognition of hydrocarbon guests by the 4:4 supramolecular complex of tris(Zn²⁺-cyclen) and trithiocyanurate is reported. Computational simulation of (2)¹²⁺–guest complexes supports its structural flexibility.

The use of dendritic structures for the grafting of core–shell γ-Fe₂O₃/polymer 300 nm superparamagnetic nanoparticles (MNPs) has been performed with four metallodendrons that were functionalized with diphosphinopalladium complexes. The catalytic performance of these nanocatalysts was optimized for the Suzuki CC cross-coupling reaction. These results demonstrated the importance of optimizing the catalytic efficiency of grafted MNPs by optimizing the dendritic structures and the nature of the peripheral phosphine ligands. All of these nanocatalysts showed remarkable reactivity towards bromoarenes and they were recovered and efficiently reused by magnetic separation with almost no loss of reactivity, even after 25 cycles.

To the very core: Core–shell γ-Fe₂O₃/polymer superparamagnetic nanoparticles (MNPs, see figure) were grafted by four metallodendrons functionalized with diphosphinopalladium complexes. These nanocatalysts were optimized for the Suzuki CC cross-coupling reaction.

Do the coupling: A palladium-catalyzed oxidative carbonylative coupling process of arylboronic acid with styrenes to chalcone has been developed. The reactions proceed under mild conditions using air as the terminal oxidant reagent.

A series of deoxycholic and cholic acid-derived oligomers were synthesized and their ability to extract hydrophilic dye molecules of different structure, size, and functional groups into nonpolar media was studied. The structure of the dye and “dendritic effect” in the extraction process was examined using absorption spectroscopy and dynamic light scattering (DLS). The efficiency of structurally preorganized oligomers in the aggregation process was evaluated by 1-anilinonaphthalene-8-sulfonic acid (ANS) fluorescence studies. The possible formation of globular structures for higher-generation molecules was investigated by molecular modeling studies and the results were correlated with the anomaly observed in the extraction process with this molecule. The ability of these molecules for selective extraction of specific dyes from blended colors is also reported.

Solubilizing insoluble dyes! A new series of cholic acid-derived dendritic structures were synthesized and their aggregation in chloroform was studied. These aggregates were used as nanocarriers for hydrophilic dye molecules in chloroform. The influence of chiral aggregates on the chiroptical properties of the dye was studied by induced circular dichroism. Finally, these molecules were investigated for selective extraction of one dye from a blended food color.

Nanoparticles meet nanotubes! Direct synthesis of TiN nanoparticles in a three-dimensional network of few-walled carbon nanotubes (FWCNTs) was achieved by using mesoporous graphitic carbon nitride (C₃N₄) as both a hard template and a nitrogen source. The TiN/FWCNT composite showed high performance for the oxygen reduction reaction in acidic media.

Stuck on you: Amine-, oxyamine-, and isocyanate-terminated self-assembled monolayers were deposited on silicon wafers for reaction with cobaltabisdicarbollide derivatives. The reaction of the isocyanate group with [NMe₄][8-NH₂-C₄H₈O₂-3,3-Co(1,2-C₂B₉H₁₀)(1,2-C₂B₉H₁₁)] gave homogeneous monolayers of cobaltabisdicarbollide moieties covalently linked to the surface (see picture).

One thing leads to another: A novel palladium(II)-catalyzed three-component domino reaction of diyne-enones with nucleophiles and vinyl ketones or acrolein under mild conditions provides efficient, general, and atom-economical access to multifunctionalized 2,3-cyclo[b]furan with a stereodefined tri- or tetrasubstituted olefin.

Instant silylene! LiBr assists the dissociation of 1,2-diaryl-1,2-dibromodisilenes. Reactions with various trapping agents gave products identical to those from corresponding reactions with aryl bromosilylenes. The reaction provides a method for the in situ generation of silylenes under mild conditions, and the reaction rate is increased by the addition of LiBr.

The crystal polymorphism of the anthelmintic drug, triclabendazole (TCB), is described. Two anhydrates (Forms I and II), three solvates, and an amorphous form have been previously mentioned. This study reports the crystal structures of Forms I (1) and II (2). These structures illustrate the uncommon phenomenon of tautomeric polymorphism. TCB exists as two tautomers A and B. Form I (Z′=2) is composed of two molecules of tautomer A while Form II (Z′=1) contains a 1:1 mixture of A and B. The polymorphs are also characterized by using other solid-state techniques (differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), PXRD, FT-IR, and NMR spectroscopy). Form I is the higher melting form (m.p.: 177 °C, ΔH_f=≈105±4 J g⁻¹) and is the more stable form at room temperature. Form II is the lower melting polymorph (m.p.: 166 °C, ΔH_f=≈86±3 J g⁻¹) and shows high kinetic stability on storage in comparison to the amorphous form but it transforms readily into Form I in a solution-mediated process. Crystal structure analysis of co-crystals 3–11 further confirms the existence of tautomeric polymorphism in TCB. In 3 and 11, tautomer A is present whereas in 4–10 the TCB molecule exists wholly as tautomer B. The DFT calculations suggest that the optimized tautomers A and B have nearly the same energies. Single point energy calculations reveal that tautomer A (in Form I) exists in two low-energy conformations, whereas in Form II both tautomers A and B exist in an unfavorable high-energy conformation, stabilized by a five-point dimer synthon. The structural and thermodynamic features of 1–11 are discussed in detail. Triclabendazole is an intriguing case in which tautomeric and conformational variations co-exist in the polymorphs.

The crystal structures of polymorphs, co-crystals, and salts of the anthelmintic drug triclabendazole are discussed in the context of an uncommon variety of polymorphism, namely, tautomeric polymorphism.

A new triarylphosphine–tertiary amine bifunctional polymeric reagent has been prepared and used effectively in a variety of one-pot Wittig reactions. The design of this reagent resolved a deficiency of a previously reported related material, and allowed it to perform more efficiently in such reactions. Furthermore, it was readily recyclable, and was also successfully applied in cascade processes involving one-pot Wittig reactions followed by either a conjugate reduction or a reductive aldol reaction. In these reaction cascades, the phosphine oxide groups generated in the Wittig reaction served as the catalyst for the subsequent reaction.

All in one pot! A recyclable, second-generation heterogeneous bifunctional polymer bearing phosphine and amine groups has been synthesized and showed enhanced utility in one-pot Wittig reactions compared to a previously reported related material. This polymer was also used in Wittig reaction cascade processes in which the oxidized polymer formed in the one-pot Wittig reaction served as the catalyst in a subsequent conjugate reduction or reductive aldol reaction (see scheme).