W Tungsten

Fluorine in bloom: A nonpolar fluorocarbon/hydrocarbon tetrablock self-assembles into a first monolayer consisting of an array of densely packed discrete circular surface micelles (dark); this layer is surmounted by a second layer of such nano-objects (light).

Cable-to-tube transition: Core-shell sulfide–carbon nanocables have been oxidised to hollow polycrystalline nanowires and further assembled to crystallites inside a transmission electron microscope. The full experimental life-cycle (see graphic) was followed for a single nanostructure providing extended structural and chemical information that support a nanocable-to-nanotube transition and the presence of the Kirkendall effect.

Bimetallic catalytic system: Palladium/copper bimetallic-catalyzed Suzuki–Miyaura-type coupling has been disclosed for direct CH arylation of azoles, instead of azole halides or pseudohalides, with arylboronic acids (see scheme).

Epoxide deoxygenation: Hydrotalcite-supported gold nanoparticles (Au/HT) efficiently catalyze the deoxygenation of epoxides to alkenes in water at room temperature under CO at atmospheric pressure and in the absence of organic solvents (see graphic). Moreover, Au/HT retains its activity and selectivity and can be reused.

Spiral up! A series of multifunctionalized benzo[5]helicene derivatives and a benzo[7]helicene were conveniently synthesized. Moreover, the oxidative cyclodehydrogenation of the benzo[5]helicenes by DDQ in trifluoroacetic acid or trifluoromethanesulfonic acid quantitatively provided the corresponding dehydro[5]helicene derivatives, which showed the cyan fluorescent properties (shown here).

Palladacadabra! The effect of ppb levels of palladium on the “copper-catalyzed” Sonogashira coupling is reported. The observed high sensitivity to palladium impurities queries the existence of pure copper catalysis in the coupling of aryl iodides and terminal acetylenes (see figure).

A dendritic nanoreactor (see graphic) constructed by 1→3 connectivity and terminated by 27 tetraethyleneglycol tethers induces ring-closing metathesis (RCM), cross metathesis (CM) and enyne metathesis (EYM) using low amounts of Grubbs-II catalyst in water and air, down to 0.04 % Grubbs catalyst for RCM. The dendrimer can be re-used at least 10 times without significant yield decrease.

On the basis of the chemistry in solution, the solid-state structures and the corresponding electronic and optical properties of dipyrrolyldiketone boron complexes as π-conjugated acyclic anion receptors have been investigated. Solid-state assemblies of the receptors exhibit anion-dependent properties that are in sharp contrast to those in the solution state. Anion complexation, along with structural differences in the pyrrole subunits such as a benzo-fused pyrrole, plays an essential role not only in the formation of the assembled modes but also in determining electronic and optical properties, as well as the charge-carrier mobilities. In addition, by anion complexation, inclusion of the counter cations into the crystals has also been found to be one of the essential factors to determine the properties.Any old (an)ion? Solid-state assemblies of π-conjugated acyclic anion receptors exhibit anion-dependent properties that are in sharp contrast to those in the solution state. Anion complexation, along with structural differences in the pyrrole subunits, such as a benzo-fused pyrrole, plays an essential role not only in the formation of the assembled modes, but also in determining the electronic and optical properties, as well as the charge-carrier mobilities (see graphic).

Reported is the first study of the influence of reactor configuration on the efficiency of a challenging ring-closing metathesis (RCM) reaction. With the intention of increasing the generality of RCM scaleup and reducing its dependence on substrate modification, macrocyclization of an unmodified, low effective-molarity diene was explored using different reactor types, in conjunction with a commercial, homogeneous Grubbs catalyst. Optimized performance is compared for a conventional batch reactor (BR), a continuous plug-flow reactor (PFR), and a continuous stirred-tank reactor (CSTR). In the PFR, maximum conversion is achieved most rapidly, but product yields and selectivity are adversely affected by co-entrapment of ethylene with the catalyst, substrate, and product in the traveling “plug”. Use of the CSTR, in which ethylene is efficiently swept out, affords an order-of-magnitude increase in total turnover numbers, and reduces the required catalyst loadings by 25× relative to the BR (to 0.2 mol %), while improving RCM yields and selectivity to quantitative levels. Continuous-flow methodologies that support liberation of the ethylene co-product thus show great promise for industrial uptake of RCM.Go with the flow: Remarkably efficient ring-closing metathesis (RCM) macrocyclization is achieved by judicious matching of reaction and reactor. In a comparative study of batch, plug-flow, and continuous stirred-tank reactors, the last example enabled significantly higher yields and selectivity, in shorter reaction times, by using 25× less catalyst (0.2 mol %) than the conventional batch reaction.

The present report develops the idea that an N-heterocyclic carbene incorporating a remote anionic functionality—here, a malonate group—as a backbone component of its heterocyclic framework, can be “post-functionalized” directly from its transition-metal complexes, upon simple addition of a variety of electrophiles interacting directly with the malonate group in the outer coordination sphere. From a palette of selected electrophilic reagents, it was thus possible to modulate the electronic donor properties of the carbene center over a rather broad range. Both the zwitterionic complex [Rh{malo-NHC}(cod)] and the cationic derivatives [Rh{malo-NHCE}(cod)]+ (where “malo-NHCE” represents the ligand modified by a selected electrophile “E”) were used as pre-catalysts in two types of catalytic reactions, namely, the polymerization of phenylacetylene and the hydroboration of styrene. The results indicate that, in both cases, the zwitterionic species is by far the best catalyst, whereas a decrease in the ligand donicity induced by the added electrophile results in a concomitant reduction of catalytic activity. Apparent deviations to such a trend in the case of the hydroboration of styrene were rationalized in terms of an interaction between the reactive catecholborane substrate and the remote functionality of the N-heterocyclic carbene leading to an in situ modification of the nature of the active species. These observations serve as a useful basis to define the scope and limitations of the present conceptual approach in catalysis.The right tone: The donor properties of a metal-bound NHC ligand possessing a malonate backbone can be finely tuned by simple addition of a selected electrophile interacting with the remote nucleophilic part of the ligand in the outer coordination sphere of the complex. Relevant consequences on the catalytic behavior of these species were observed and rationalized on the basis of two test catalytic reactions.