Chemistry - A European Journal

The cover picture shows the frontispieces of the Concept, Review, and Minireview articles published in this issue, highlighting the diverse range of chemistry that will be covered at the 3rd European Chemistry Congress in Nürnberg. They represent five of the seven main symposium topics: Innovative Materials, Catalysis, Molecular Life Sciences, Analysis, Manipulation and Simulation, and Advances in Organic and Inorganic Chemistry. In the top row from left to right: H. Möhwald, T. Nakanishi et al. (page 9330 ff.), H.-J. Freund (page 9384 ff.), and K. Landfester and A. Ethirajan (page 9398 ff.). In the middle row from left to right: F. Würthner and K. Meerholz (page 9366 ff), M. Orfanopoulos and M. N. Alberti (page 9414 ff), and J. V. Sinisterra et al. (page 9422 ff.). In the bottom row from left to right: P. Baglioni et al. (page 9374 ff), M. Rueping et al. (page 9350 ff.), and Bert Weckhuysen et al. (page 9340 ff.) (Cover designed by Heulwen M. M. Price).

ChemistryViews.org is a comprehensive free-to-view news and information site with an associated magazine, ChemViews, provided by ChemPubSoc Europe and its publisher, Wiley-VCH. The new site enhances ChemPubSoc Europe's and Wiley-VCH's suite of market-leading peer-reviewed journals like Chemistry—A European Journal. ChemViews offers news, commentary, opinion, and additional feature material from leading authors to the global chemistry community. Sign in for a free newsletter at www.ChemViews.org (cover by Heulwen M. M. Price).

Uncommonly good: An unusual amphiphile composed strictly of hydrophobic units, fullerene (C₆₀), and long aliphatic chains behaves as an uncommon surfactant in organic media. Slight differences in the polarity and the chemical nature among these groups allow them to exhibit amphiphilicity. Their material aspects were also investigated (see graphic).

Molecules, line up! Synchrotron-based IR and UV/Vis microspectroscopic data and complementary theoretical calculations can be used to unambiguously identify transient carbocationic species generated in the acid-catalyzed oligomerization of styrene derivatives within ZSM-5. Polarization dependence of the IR and UV/Vis spectra is rationalized in terms of the vibrational and electronic transitions occurring in the confined molecules (see figure).

Combining acids and metals! The combination of chiral Brønsted acids and achiral or chiral transition-metal complexes emerged as a new strategy in asymmetric synthesis. The merged catalytic approach provides practical synthetic protocols that enable the synthesis of a broad range of compounds in a highly enantioselective fashion (see graphic).

Get organized! The recent successful utilization of highly dipolar merocyanine dyes in bulk heterojunction organic photovoltaic materials provides a convincing example for illustrating the importance of supramolecular organization principles in multifunctional organic materials.

Paint the town red! Sulfation of wall paintings produces flaking and powdering of the paint layer. The combined action of calcium and barium hydroxide nanoparticles provides complete immobilisation of salts, and a durable re-cohesion effect on the paint layer (see graphic). The original carbonation process is re-generated to perfectly match the original physicochemical properties of the painting.

Scratching the surface: In this Review models for heterogeneous catalysis are discussed based on a surface-science approach (see figure). It is shown that models catching part of the complexity of the real system, which is connected with the finite size of active components and the flexibility of the arrangement of atoms in the active component, play an important part in determining the activity and selectivity of the system.

Close to the bone! Polymer nanoparticles can be used as versatile biomimetic templates to produce hybrid particles by employing either the volume or the surface of the polymer nanoparticle as templates (see picture). Such a concept is used to produce nanoparticles containing the bone mineral hydroxyapatite as the inorganic material. These particles could find application as regenerative fillers or as a scaffold for nucleation and growth of new bone material.

Concerted or stepwise? Recently, the mechanism of the singlet oxygen ene reaction has been a subject of renewed interest, particularly, whether the reaction is concerted or involves discrete intermediates. The majority of experimental and computational studies support a traditional stepwise mechanism involving a perepoxide-like intermediate (see scheme). This Minireview highlights some of the classical and most recent theoretical and experimental results relating to the mechanism of the ¹O₂ ene oxyfunctionalization.

The future is bio, the future is green: Interest in implementing sustainable industrial technologies has propelled the use of biocatalysts (enzymes or cells), leading to high chemo-, regio- and stereoselectivity under mild conditions. We focus on different attempts to combine the valuable properties of green solvents with the advantages of using biocatalysts for developing cleaner synthetic processes (see figure).

En route to madangamines: A unified strategy has been developed for the enantioselective assembly of functionalized diazatricyclic synthetic precursors of madangamines (see scheme; Bn=benzyl, Boc=tert-butoxycarbonyl, Mbs=para-methoxybenzenesulfonyl).

Being selective: The catalytic allylation of α,β-unsaturated aldehydes with allyltrichlorosilane in the presence of chiral 3,3′-unsymmetrically substituted bis(tetrahydroisoquinoline) N,N-dioxides was explored. The allylation of various aldehydes proceeded under mild reaction conditions (−78 °C) with high yields and enantioselectivity (see scheme). This allylation was applied in the synthesis of (S)-(−)-goniothalamin.

CO and NO give NCO and O! Sequential treatment of [U(η-C₈H₆{SiiPr₃-1,4}₂)(η-Cp*)] with CO followed by NO (or vice versa) affords a mixture of the bridging cyanate complex [{U(η-C₈H₆{SiiPr₃-1,4}₂)(η-Cp*)}₂(μ-OCN)₂] and the bridging oxo complex [{U(η-C₈H₆{SiiPr₃-1,4}₂)(η-Cp*)}₂(μ-O)], both of which have been structurally characterised (see scheme).

“Catch-and-release”: Simple alk-1-enes are effective at liberating buta-1,3-dienes from vinyl alkylidene ruthenium complexes, as well as undergoing alkene–alkylidene exchange with enyne substrates to regenerate the alk-1-ene. This ability to “catch-and-release” ruthenium alkylidenes allows alk-1-enes higher than ethylene (“Mori's conditions”) to be used as a co-catalysts in terminal enyne metathesis with the Grubbs generation I complex (L=PCy₃).

Quick off the mark! In this work we present the first highly enatioselective oxa-Michael/aza-Baylis–Hillman tandem reaction between 2-alkynals and salicyl N-tosylimine leading to optically active 4-amino-4H-chromenes (see scheme). This reaction takes place in less than 2 h with high yields and excellent enantioselectivities.

Hot alkyne! The in situ generation of ethynyl-1,2-benziodoxol-3(1H)-one (EBX) from a silyl-protected reagent by using TBAF is reported. EBX displayed exceptional acetylene transfer ability onto stabilized enolates (see scheme), even at −78 °C. The mild reaction conditions allowed the first ethynylation reactions of linear keto, cyano, and nitro esters in high yields to give all-carbon quaternary centers or non-natural amino acids after selective reduction of the nitro group.

Microgel grow-bags: Surface-enhanced Raman scattering (SERS)-active bimetallic core–shell spheres can be grown inside poly(N-isopropylacrylamide) (pNIPAM) microgels (see figure).

Chemical clusters: The reversible reaction of Brønsted acids, HA, with the hexanuclear dihydride {Pt₆}H₂ ({Pt₆}=Pt₆(μ-PtBu₂)(CO)₄) affords anion-bonded {Pt₆}A₂, which reacts with dimethoxyethane to give the linear, cluster-containing polymer [Pt₆(μ-PtBu₂)₄(CO)₄(CH₂OCH₂CH₂OCH₂)]_x (see figure).

A golden combination: A direct asymmetric one-pot synthesis of optically active 2,3-dihydropyrroles from simple precursors is presented. The approach is based on a bifunctional organocatalytic Mannich-type reaction followed by Au^I-catalyzed alkyne hydroamination (see scheme; TFA=trifluoroacetic acid). To highlight the synthetic potential of the accessed heterocyclic compounds, their transformation into 1-pyrrolines is presented.

Active alkanes: Gaseous alkanes (ethane, propane and n-butane) efficiently react with carbon monoxide and water to give selectively, in a single-pot, the corresponding carboxylic acids in a metal-free and acid-solvent-free aqueous medium, under mild conditions (see figure).

The perfect couple! The mechanism of the palladium-catalyzed intermolecular ene–yne coupling (see scheme) has been characterized by DFT. The absence of potential by-products from homocoupling could be fully rationalized.

An amphiphilic receptor (1) transports N-acetylated amino acid carboxylates across a bulk liquid membrane (see graphic). In single experiments the release of the substrate determines the transport rate, whereas in competition experiments the affinity towards the receptor is decisive. Since 1 can only bind carboxylates in its protonated form, an overall symport of the amino acid carboxylate and a proton occurs. This allows for pH gradient driven active transport of the substrate.

Clear as liquid crystals! New liquid-crystalline materials (see figure) were prepared by self-assembly driven by halogen bonding (XB) between a range of alkoxystilbazoles (XB acceptors) and derivatives of the 4-iodotetrafluorophenyl unit (XB donors). Despite the fact that the starting materials are not mesomorphic, the dimeric, halogen-bonded complexes obtained exhibited nematic and SmA phases, depending on the length of the alkyl chains present on the components.

Nature's diversity: Kinetic resolution of structurally different aliphatic β-amino ketones was performed by using a collection of 16 different Baeyer–Villiger monooxygenases from various bacterial origins (see scheme). Excellent enantioselectivities for both normal and antipodal esters were observed and hydrolysis of Baeyer–Villiger esters yielded enantiopure β-amino alcohols.

Model behaviour: A nanostructural model for the adsorption of CO on powder Au/ceria–zirconia catalysts, under conditions relevant to catalysis, is proposed by combining electron microscopy, computer modelling (see figure) and chemical analysis. This model highlights the key role of CO spillover in the adsorption on ceria–zirconia.

Stick together! The aggregation of amphiphilic polycarboxylates in water to structured micelles is strongly determined by the nature of the counterion. Sodium ions show the most pronounced counterion effect, favoring both intra- and intermicellar aggregation (see figure).

High-oxidation state bis-oxazoline rhenium(V)–oxo complexes (see scheme) catalyze the enantioselective reduction of ketones and imines under open-flask conditions. Additionally, the oxo complexes promote a tandem [3,3]-rearrangement–enantioselective reduction of propargyl and allenic alcohols.

In search of scaffold diversity: The synthesis of a library of small molecules with high scaffold diversity is described. Initially, metathesis substrates were assembled from combinations of two or three building blocks. The range of scaffolds was extended through the subsequent exploitation of inter- and intramolecular Diels–Alder reactions. Fluorous tagging was used to facilitate the synthesis and functionalisation of the products (see scheme).

Tungsten is better: Compound [Cp*₂W₂O₅] is 50 times more active than [Cp*₂Mo₂O₅] for the quantitative and selective epoxidation of cyclooctene by H₂O₂ in acetonitrile (see scheme). A DFT study traces this difference to the greater oxophilicity of tungsten, which plays a determining role in the transition-state stabilisation.

Safety catch: The solid-phase synthesis of differently lipidated peptides from the N-Ras family with the safety-catch sulfonamide linker has been established, including amino acid loading, peptide assembly and peptide release. The key step is the release of a pre-peptide from the solid support with the C-terminal amino acid methyl ester under microwave irradiation (see scheme).

When charge transfer meets aromaticity: Charge transfer across quinoid and expanded quinoid π spacers was found to be highly efficient in conjunction with the aromatization of the spacer units based on experimental and theoretical evidence. A push–pull tetrakis(ethynediyl)-expanded quinoid compound (see figure) represents the first proaromatic radiaannulene, featuring a 14 π-electron perimeter in the charge-transfer geometry.

A novel synthetic strategy involving palladium-catalyzed Sonogashira reactions and iron-catalyzed double carbonylations allows for the synthesis of biologically interesting 3,4-diaryl-substituted succinimides and maleimides (see scheme).

The unnatural antibiotic iso-platencin, which is about as active as natural platencin (a novel antibiotic which is active against multiresistant pathogens), but much more selective, is presented as a new antibiotic lead structure (see figure). We describe efficient syntheses of three platencin analogues of varying activities, which allow further conclusions about the pharmacophoric part of the molecule.

Accessing Ce^IV: The tetravalent oxidation state of cerium is unusual and often associated with multiconfigurational behaviour. Analysis of the bonding in tetravalent, rather than more conventional trivalent, f-block complexes shows the 5f metal bonds to softer ligands are stronger and more covalent than 4f analogues (see scheme). The use of trityl chloride as a simple oxidant to access Ce^IV is also shown.

Resistance is futile! Computer-assisted protein modeling and parallel virtual screening led to the identification of antibiotic agents that combat clinically relevant drug-resistant Staphylococcus aureus. The non-nucleoside inhibitors target bacterial thymidine kinase (see figure).

The higher the better: We have realized the rarely found scenario of a charge transfer that commences in a higher-energy excited state (see image), through the careful choice of electron donor and electron acceptor.

Give it the green light! The luminescence properties of M₃Si₆O₁₂N₂:Eu²⁺ (M=Ba,Sr) render this layered Ba–oxonitridosilicate an interesting phosphor for pc-LEDs. Various improved syntheses lead to highly crystalline products as well as single crystals suitable for precise structure determination (see figure). In situ high-pressure and high-temperature investigations indicate the best sintering conditions. XES and XAS spectra were conducted for a better understanding of the electronic structure.

Homogeneous or heterogeneous? A combined approach by using catalytic experiments and in situ XANES spectroscopy was used to clarify the heterogeneous or homogeneous nature of the Pd/Al₂O₃(R)-BINAP catalyst system (see graphic) applied in the enantioselective allylic alkylation of (E)-1,3-diphenylallyl acetate. Crucial factors that cause leaching were identified.

Superoxo magic: The oxidizing ability of an isolable and thermally stable superoxo–nickel(II) towards exogenous organic substrates has been studied for the first time in detail (see scheme). The complex is suitable to oxidize OH and NH bonds and even shows a unique dioxygenase-like reactivity towards phenols to give unexpected oxidation products.

Temporary control: The easily installed and removed N-(2-pyridyl)sulfonyl group directs the CH functionalisation of indoles with complete regiocontrol for C2 and allows the final N deprotection by facile, reductive NS cleavage (see scheme). This concept has been successfully applied to the C2H alkenylation of indoles and pyrroles as well as to the dehydrogenative intermolecular homocoupling of indoles to afford 2,2′-biindoles.