Chemistry - A European Journal

An eye for molecules on a surface. In the Full Paper by D. Gatteschi et al. on page 7530 ff., synchrotron light has been employed to investigate the chemical and magnetic nature of monolayers of sulfur-functionalized Mn₁₂ clusters grafted on gold substrates to reveal significant reduction of the manganese atoms and the disappearance of the typical magnetic hysteresis.

From test tubes to pilot plants: A personal account on more than ten years of research concerning telomerisation and dimerisation reactions (see scheme) is presented. The development of N-heterocyclic carbene based palladium catalysts is highlighted that have been applied on industrial pilot-plant scale.

Precious interactions: Combinations of dendrimers and DNA are described as well as the various aspects of the interactions: a) DNA can be the structural constituent of dendrimers; b) dendrimers can be used as 3D linkers for improving the sensitivity of biosensors; and c) dendrimers are efficient vectors of DNA to penetrate inside cells through electrostatic interactions, in view of genetic therapy.

Sweet mimicry: This short overview covers recent efforts towards design and synthesis of glycomimetic inhibitors (three examples of which are shown here) of well-known target lectins (cholera toxin, DC-SIGN).

Standing in line: The alignment of dye molecules in the channels of zeolite L can be extended to the macroscopic scale by preparing monolayers of crystals with defined morphology (see graphic). Systems including multiple types of dye monomers form the basis for the design of novel device architectures in the field of optical and photoelectronic applications.

Speedy reaction: Flash chemistry is defined as a field of chemical synthesis in which extremely fast reactions are conducted in a highly controlled manner to produce desired compounds with high selectivity. This article provides a brief outline of the concept of flash chemistry using microreactors and its applications to organic synthesis and polymer synthesis.

How to improve efficiency! The one-pot transformation of various alkynyl derivatives into functionalized homoallylic alcohols and amines (see scheme) can be easily performed through a combination of carbometalation, zinc homologation, and allylation reactions.

Go with the flow: Chemical reactions in continuous-flow microstructured devices (see graphic) are described by fluid dynamics, transport phenomena and reaction kinetics. They enable the investigation of complex chemical reactions in the laboratory and the low-risk scale-up to high production rates.

Chemically significant mesoporous materials with tunable pore size and pore length could be controlled effectively. Monodisperse metal nanoparticles with tunable particles size have been encapsulated within the mesoporous materials (see graphic) by various strategies, especially by a facile autoreduction route.

Sugars against sticky bacteria: A panel of glycomolecules (an example of which is shown here) for the inhibition of bacterial adhesion on host glycoconjugates is described.

Cultivating hybrids: The synthesis of new hybrid aerobic oxidation catalysts that include an oxygen-activating motif and a hydroquinone is reported. These hybrid catalysts proved to be efficient for the aerobic reoxidation of palladium and ruthenium catalysts in a set of test oxidations (see graphic).

New family member: A conceptually new family of modular aminal–pyrrolidine organocatalysts was prepared by diversity-oriented synthesis. The catalytic properties of these organocatalysts could easily be tuned by varying the different substituents on the aminal part. Good yields and enantioselectivities up to 91 % were obtained in Michael additions to nitroolefins or vinyl sulfones (see scheme).

A new sequential [n+2] cycloaddition/CH insertion reaction of indolylalkynyl and ortho-aminophenylalkynyl Fischer carbene complexes that leads to azepino[3,2,1-hi]indole, benzazepine, and indole derivatives is described. As an extension of this chemical behavior, 1,2-disubstituted indoles can be obtained from methoxy ortho-aminophenyl Fischer carbene complexes (see scheme).

Highly chemo- and enantioselective hydrogenations of linear β,β-disubstituted enones (see scheme) have been accomplished by using iridium complexes 1 a–i bearing chiral sulfoximine-type P,N-ligands. The catalyst system preferentially hydrogenates the CC double bonds giving saturated ketones as the major products. Substrates with bulky substituents at the β-position give the best enantioselectivities. Thus, enones with isopropyl and cyclohexyl substituents afford ketones with 97 % ee (at >95 % conversion).

Pharmacophore signature at glance: INPHARMA NOE interactions can be measured between two ligands that bind competitively to a common macromolecular receptor, and can be interpreted quantitatively to derive the binding mode of the two ligands. This approach relies on computationally demanding full relaxation matrix calculations. Here we demonstrate that the INPHARMA NOEs measured in the presence of a selectively-protonated receptor (see figure) can be interpreted in a semiquantitative way to discriminate between binding poses, thus relieving for the need of demanding computations.

To dimerize or not to dimerize: The crystal structure of β-cyano-neocobyric acid reveals a new vitamin B₁₂ dimerization motif (see figure) that involves α-face interactions and Co-coordinated f-propionate side chains. This motif is reminiscent of the carboxylate-bonded heme dimer in β-haematin and hemozoin, the disposal form of heme in Plasmodium malaria.

A simple two-component sensor system was developed, featuring the strongly Lewis acidic (but air-stable) Fc^RBMes₂ (1: Fc^R=(η⁵-C₅H₄)Fe(η⁵-C₅R₅), R=H, Me; Mes=2,4,6-Me₃C₆H₂), which can be shown to bind both fluoride AND cyanide in solution (but not other anions), and the weaker boronic ester Lewis acid Fc^RB(OR)₂ (2: (OR)₂=R,R-OC(H)PhC(H)PhO), which signals the presence of fluoride but NOT cyanide in solution. By coupling the electrochemical shifts with a suitable redox-active tetrazolium dye, a colorimetric AND/NOT sensor system for fluoride and cyanide ions can be developed (see picture).

Cold experiments: The first low temperature XAS/XMCD study of Mn₁₂ adsorbates on gold reveals an intrinsic redox-instability of the clusters (see figure) and highlights the potential of the XAS/XMCD technique to probe the behaviour of molecular magnets at surfaces.

Different bearings: A series of Ru–olefin complexes bearing different L-type ligands were synthesized and characterized by NMR spectroscopy and X-ray crystallography. Only evidence for side-bound isomers was observed (see graphic).

The next generation: A series of ruthenium-based metathesis catalysts bearing unsymmetrical N-heterocyclic carbene ligands were synthesized and fully characterized. Their catalytic activity was evaluated in a variety of benchmark ring-closing metathesis, ring-opening metathesis polymerization, and cross metathesis reactions (see figure). The electronic properties of the new carbenes were also studied in the corresponding [Rh(CO)₂Cl(NHC)] complexes.

Conformation analysis: NMR experiments followed by a docking procedure have allowed the microtubule-bound conformations of discodermolide (DDM) and dictyostatin (DCT), two microtubule-stabilizing agents, to be deduced. Superimpositions of the NMR-derived bound conformers of DDM (yellow) and DCT (violet) on paclitaxel (green) are shown. According to these models, paclitaxel provides additional contacts with tubulin by using the extended side chain.

Recognition of simple sugars, with different stereochemistries, by aromatic entities (such as depicted), including phenol and the aromatic amino acids, has been studied by NMR (chemical shift perturbations, NOE experiments) assisted by molecular mechanics and DFT calculations, as model systems for naturally occurring protein–carbohydrate interactions.

Metallothionein necklaces: Electrospray mass spectrometry of concatenated Cd₄S₁₁ domains (an example of which is depicted here) shows differential demetallation that can be interpreted by molecular dynamics calculations.

A carbenoid–radical intermediate is responsible for formation of a C₃-bridged dinuclear iridium species upon reaction of a mononuclear Ir^II–ethene complex with ethyl diazoacetate in MeCN. The analogous reaction with trimethylsilyldiazomethane leads to a mononuclear Ir^III–CH₂SiMe₃ species through hydrogen-atom abstraction.

Keeping functional groups at bay: The introduction of functional groups to the “bay” region of perylene tetracarboxylic diimides significantly influences surface-based self-assembly processes leading to either unimolecular or bimolecular hexagonal surface networks, exploiting either homo- or hetero-molecular hydrogen bonding.

Iron complexes with non-innocent ligands: The detailed investigation of the electronic structures of a series of iron complexes with redox active o-phenylenediamide(2−) derived ligands by means of crystallography, magnetochemistry, spectroscopic methods, and density functional calculations is presented. [Fe^III(L^.−)(L²⁻)] (S_Fe=3/2; S_t=1) possesses the depicted electronic structure with delocalized ligand mixed valency.

Controlling polymerization: Experimental and computational studies show how solvent coordination can fine-tune the [Co^II(acac)₂] system for the synthesis of well-controlled poly(acrylonitrile) (PAN) and poly(vinyl acetate)-b-poly(acrylonitrile) (PVAc-b-PAN) block copolymers (see scheme).

Spin and charge confinement: One-electron-reduced and -oxidized stages of donor-substituted 1,1,4,4-tetracyanobuta-1,3-dienes (TCBDs) were generated by chemical methods and studied by using EPR spectroscopy (see figure). In radical anions, confinement of spin and charge to the electron-withdrawing TCBD moieties was observed. In radical cations, an analogous charge and spin localization to the electron-donating moieties was found.

Catalytic asymmetric desymmetrization: The dinuclear zinc-catalyzed asymmetric desymmetrization of acyclic 2-substituted-1,3-propanediols provides several 2-alkyl-, 2-alkoxy-, and 2-aryl-1,3-propanediols (see scheme). Further elaboration of the products provides several useful chiral building blocks for natural product synthesis.

Sense and sensitivity: The immobilisation of fluorescent dendrimers improves their sensing properties. Fluorescent dendrimers show enhanced selectivity towards hazardous phenolic compounds after being grafted onto mesoporous titania films and have potential applications as sensors (see graphic). This effect is a result of the increased spatial proximity of the fluorescent molecules, which is induced by pore confinement.

Tuning communication: The effect of ortho, meta and para isomeric connections on the electronic communication between subphthalocyanine and C₆₀ in molecular systems that can give rise to energy- or electron-transfer mechanisms (see graphic) have been analyzed.

Triplets! A functional equivalent of [Rh{(tBu₂PCH₂SiMe₂)₂N}] reacts with N₂O to give [RhO(PNP)], which has a triplet ground state. The related dioxygen complex was also investigated (see picture).

Benzyl makes the difference! The N-benzyl-substituted (S,S)-1 is the key to the realization of the title reaction, in which the asymmetric epoxidation of aromatic alkenes with aqueous hydrogen peroxide proceeds smoothly at room temperature in the presence of simple Fe salts and pyridine-2,6-dicaroxylic acid (H₂(pydic)).

The mechanism of aqueous-phase asymmetric transfer hydrogenation (see scheme) of acetophenone with HCOONa catalyzed by Ru-TsDPEN has been investigated by stoichiometric reactions, NMR probing, kinetic and isotope effect measurements, DFT modeling, and X-ray structure analysis.