Chemistry - A European Journal

A mixed-ligand system of Pd/Synphos/Xantphos promotes effective CN coupling in the synthesis of various N-arylaminotriazole and N-arylaminopurine nucleoside analogues. This catalytic system is strikingly powerful and efficient, allowing for unparalleled substrate scope and high product yields as well as promotion of CCl bond activation for CN coupling. ³¹P NMR investigations provided useful evidence favoring a mechanism in which the catalytic reactions are mediated by ligand exchange during both Pd catalyst formation and oxidative insertion. For more details see the Communication by L. Peng et al. on page 2221 ff.

Glowing hybrids: An organic–inorganic approach has generated a variety of light-harvesting hybrid assemblies, with different physical nature based on their design (see scheme). These design concepts (covalent, semicovalent, and noncovalent approaches) are discussed with respect to the synthesis of artificial photosynthetic hybrids (MOF=metal–organic framework; PMO=periodic mesoporous organosilica).

Cyclopropane rings true: By selecting the appropriate substituents on the ester and silyl groups, fused cyclopentane derivatives with multiple contiguous stereocenters can be synthesized with excellent diastereoselectivity through Cu^II/bisoxazoline-catalyzed intermolecular [3+2] cycloaddition reactions of cyclopropane-1,1-dicarboxylates and cyclic enol silyl ethers (see scheme).

Two nutrients in one molecule: A zwitterionic λ⁵Si,λ⁵Si′-disilicate (1) was synthesized and characterized. It contains ligands that exclusively derive from natural products ((R,R)-tartaric acid, choline). Hydrolysis of 1 yields 2, which shows a remarkable kinetic stability in water. Upon dissolution of 1 and 2 in water, the nutrients choline and orthosilicic acid are formed by hydrolysis

Quick and easy detection: The Exo III-stimulated regeneration of the analyte by the digestion of supramolecular aptamer–analyte complexes provides a means to develop amplified optical aptasensors (see figure).

It's do or diaminate: The selective diamination of 1,3-butadienes in the presence of hypervalent iodine reagents has been developed. This oxidation process proceeds with complete selectivity in favor of diamination. Depending on the substrate, it proceeds either with 1,2- or 1,4-regioselectivity (see scheme).

Minor isomer comes forward: Minor isomer C₈₄(5) has been captured by high temperature trifluoromethylation with CF₃I and chlorination with VCl₄. The compounds C₈₄(CF₃)₁₆, C₈₄Cl₂₀, and C₈₄(5)Cl₃₂ were investigated by X-ray crystallography providing the first direct proof of the cage connectivity of D₂-C₈₄(5). The D₂-C₈₄(5)Cl₃₂ molecule (see figure; C grey, Cl green) contains two flattened, pyrene-like substructures on opposite poles of the cage resulting in its drum-like shape.

Make it unique! A mixed-ligand system of Pd/Synphos/Xantphos promotes effective CN coupling in the synthesis of various N-arylaminotriazole and N-arylaminopurine nucleoside analogues. This catalytic system is strikingly powerful and efficient, allowing for unparalleled substrate scope and high product yields as well as promotion of CCl bond activation for CN coupling (see scheme).

Just add O₂: Based on the fact that an oxygen-adsorbed Pd metal surface shows higher reactivity for water dissociation than a clean Pd surface, carbon-supported Pd nanoparticles (NPs) with surface oxygen atoms were developed as a highly effective and reusable heterogeneous catalyst for selective oxidation of silanes to silanols with water as a green oxidant (see figure).

Polyene synthesis: An efficient approach to the total synthesis of polyene natural product dihydroxrulin (1) is described. A novel, mild, direct organocatalytic IBX-mediated dehydrogenation process of simple alcohols to enals has been developed, which serves as a key step in the synthesis (see scheme).

Let's get charged! Positively charged nanoparticles (NPs) spontaneously self-assemble into hexagonally close-packed lattices at a planar CH₂Cl₂–water interface (see figure). The self-assembly process is fully autonomous and occurs without any external manipulation.

Let the protons flow: The synthesis of a core–shell macromolecule bearing phosphonic acids is presented. The rigid central core serves as a scaffold to stabilize the flexible polymer shells. Pronounced proton conductivity is obtained under humidified conditions. The self-assembly of such dendritic macromolecules by electrostatic interactions on a modified gold substrate is investigated and characterized.

Designer photoresponsive assemblies: Oligothiophenes and diarylethenes are held together by multiple hydrogen bonds, affording photoresponsive and electroactive supramolecular copolymers. The co-polymer chains hierarchically organize into helical nanorods, which can be reversibly converted to small oligomeric species upon irradiation with UV and visible light (see figure).

Boron goes liquid? The first syntheses of pure ionic liquids (ILs) with [BH₄]⁻ and [B₃H₈]⁻ ions were realized as one-step reactions (see figure). These boranate ILs are suitable reagents for synthesis and have a potential for redox shuttling and storage/release of H₂.

Mix masters: Mixed colloidal suspensions of reduced graphene oxide (RGO) and layered MnO₂ nanosheets were synthesized (see figure) and applied as precursors for the synthesis of nanocomposites and hybrid films of RGO/MnO₂.

Even spread: Precipitation of barium carbonate in silica-rich media at high pH yields hierarchically structured polycrystalline materials, termed silica–carbonate biomorphs, which exhibit complex curved shapes. Determination of microscopic growth rates and reagent concentration profiles (see figure) helped to elucidate the chemistry underlying the formation of these materials and provided insight into growth kinetics and morphogenetic aspects.

New facets of SnO₂: A morphology evolution of rutile SnO₂ nanocrystals from low-energy facets to high-energy facets (see figure) is achieved in a basic environment. Our experimental results demonstrate that the catalytic activity of the crystal facets for CO oxidation follow the sequence {111}>{221}>{101}>{110}, whereas the gas-sensing properties of crystal surfaces is in order {221}>{111}≫{101}>{110}.

“L” is right: Introduction of an L-amino acid spacer in a polymer-supported bifunctional catalyst, based on a chiral diamine, imparts outstanding activity and stereoselectivity in nitro-Michael addition, whereas D-amino acids are a poor match for the particular diamine configuration (see scheme). The reactivity patterns of the new catalysts shed light on the reaction mechanism and the CC bond-forming transition state.

Responsive polyions! Two oppositely charged polypeptide-based copolymers have been successfully synthesized. A mixture of these copolymers in aqueous solution led to PIC micelles that exhibit thermo- and pH-sensitivity. The PIC micelles were fluorescently labeled with Rhodamine B and 5-aminofluorescein to give novel multicolored PIC micelles, the fluorescence properties of which could be controlled by variation of the temperature or pH (see figure).

Complex chemistry! The mechanism for the formation of tungstite nanoparticles (see figure) has been investigated by time-dependent gas chromatography and X-ray diffraction as well as by time-resolved in situ X-ray absorption near-edge structure and extended X-ray absorption fine structure spectroscopy.

Complete selectivity switch from dehydrogenation to oxidative-coupling of alcohol and dimethylamine to form the corresponding amide on atomic-oxygen-activated Au(111) is reached through the efficient removal of the excess atomic oxygen by molecularly adsorbed alcohol (see scheme).

Ta Ta for now: CC coupling processes on a tantalum-bound pincer ligand give rise to a series of tantalum derivatives with a variety of tetradentate ligands (see figure). The role of the ligand substituents on the reactivity and properties of the corresponding complexes is discussed.

Monohaloboryl ligands: Reaction of transition-metal–dihaloboryl complexes of the form [L_nMBX₂] with K[(η⁵-C₅H₅)MnH(CO)₂], leads, via salt elimination, migration of the Mn-bound hydride onto the B atom, and loss of HX, to the formation of metalloborylenes.

Movin' on up: Uniform and monodisperse upconversion core/mesoporous silica shell structured nanocomposites of sub-50 nm diameter were successfully synthesized (see figure). Multifunctional bioapplications of the synthesized nanocomposite particles for simultaneous magnetic resonance and upconversion fluorescence imaging are presented.

Game over—structure solved: A combination of labeling experiments with mass spectrometry results in the reliable determination of the sum formula, the nature of the building blocks, and (for peptide natural products) also the determination of the absolute configuration as exemplified for the novel natural products GameXPeptide A–D (see scheme).

A state of flux: Diarylphosphido diphosphine zinc complexes show fluxional behavior and efficiently promote the ring-opening polymerization (ROP) of ε-caprolactone (CL) and L- and rac-lactide (LA), as well as copolymerization of CL and LA, under mild conditions to give polyCL (PCL), PLA, and CL–LA copolymers, respectively (see scheme).

Treescape: The tetrameric assembly of dendrons through G-quadruplex formation (see figure) is reported. The dynamic character of the self-assembly process can be exploited to create dendrimers with thermoresponsive behavior that can be tuned over a wide temperature range. The approach also promises access to many different dendrimers by using the combination of varied components.

The mesogenic behaviours of six tripedes based around two stereogenic cores were investigated. The major result concerns the transfer of the chiral information from the central core to the periphery and the effect on mesomorphic properties. These properties were fine-tuned by incorporating functional moieties within the chiral core without modifying its stereogenicity.

Forming an OO bond: The bis(ruthenium–bipyridine) complex [Ru₂(μ-Cl)(bpy)₂(btpyan)](BF₄)₃ ([1](BF₄)₃; bpy=2,2′-bipyridine, btpyan=1,8-bis(2,2′:6′,2′′-terpyrid-4′-yl)anthracene; see the scheme) catalyzes the chemical and electrochemical oxidation of water. Resonance Raman spectroscopic measurements of the oxidized form of the [1]³⁺ ion revealed the formation of a [Ru₂(bpy)₂(btpyan)(μ-O₂)]⁴⁺ ion through the intramolecular coupling of two Ru^IVO units.

Exceed the limits! Cyclopenta[b]dihydrofuran derivatives are easily accessed through a one-pot Knoevenagel-initiated cascade approach (see scheme; EDDA=ethylenediammonium diacetate) by starting from simple precursors. A new type of carbonyl polyene system that displays unprecedented reactivity has been established.

Contortionist molecules: Flexible tris(2- and 3-ureidobenzyl)amines with C_s symmetry self-assemble to give mixtures of regioisomeric capsular aggregates (see figure). Of special significance is the efficient self-assembly of a more flexible triurea endowed with a ureidopropylic arm.

As easy as O to C: The ability of a series of tetrahydropyrimidine-based isothioureas to promote the asymmetric Steglich reaction has been evaluated (see scheme). Good to excellent levels of enantioselectivity were generally observed for the rearrangement of oxazolyl carbonates, with markedly different catalytic efficiencies observed with variation of the stereodirecting group(s). Crossover and dynamic ¹⁹F NMR experiments were also used to develop a mechanistic understanding of this transformation.

Closing the ring: Appropriate anions can act as specific kinetic templates for the ring-closing step in macrocyclisation reactions of pseudopeptides, through supramolecular interactions at the transition state (see figure).

Iron adds it: Allylic carbonates react with various activated olefins in an Fe-catalyzed decarboxylative alkoxy allylation to afford densely substituted products in good yields and with high regioselectivities under mild conditions (see scheme). The robustness of the catalytic system is demonstrated by the first Fe-catalyzed alkoxy allylation allylic sulfenylation and three-component coupling sequence.

Twist to the left: The left-handed (M) 3₁₀ and α helices of (3S,4S)-1-amino-3,4-(dialkoxy)cyclopentanecarboxylic acid (R: methyl or methoxymethyl) homochiral homopeptides (see structure of methyl decapeptide; Cbz: benzyloxycarbonyl) are exclusively controlled by the side-chain chiral centers, because the cyclic amino acid does not have an α-carbon chiral center but has side-chain γ-carbon chiral centers (see figure). The oligopeptides can be well dissolved in pure water and are more α helical in water than in 2,2,2-trifluoroethanol solution.

Chiral nonracemic propargylic amines with Cbz protection (see scheme) have been prepared by the addition of terminal alkynes to imines generated in situ from α-amido sulfones in the presence of diethylzinc and BINOL-type ligands as catalysts. The reactions give good yields and high enantioselectivities (ee values up to 95 %) for a good number of aromatic and heteroaromatic α-amido sulfones and alkynes.