Chemistry - A European Journal

State-of-the-Art first-principle molecular dynamics and metadynamics simulations in an explicit periodic solvent model, together with new NMR experiments are used by V. Van Speybroeck, N. De Kimpe et al. in their Communication on page 580 ff., to provide extensive and convincing evidence for the solvation and isomerization properties of lithiated 3-chloro-1-azaallylic anions in tetrahydrofuran.

Bio-inspired chemistry! Photochemical key steps (see figure) provide a versatile tool for the remote control of chemical and biological processes. Many challenging reactions, which otherwise could hardly be achieved at all, are readily triggered and powered by photons. This Concept article explores the design principles and potential applications of biomimetic catalysis based on photoresponsive molecular systems.

Long live theZisomer! The solvation and isomerization properties of lithiated 3-chloro-1-azaallylic anions in tetrahydrofuran are revealed. Extensive and convincing evidence is obtained from state-of-the-art first-principle molecular dynamics and metadynamics simulations in an explicit periodic solvent model, together with detailed NMR experiments.

Estimates of intramolecular distances are essential for structure determination (see figure). For medium-sized molecules, ROESY NMR spectroscopy is the method of choice for obtaining distances. However, the integration of ROESY cross-peaks is problematic, owing to the offset dependence of the integrals and/or TOCSY artefacts. We here present EASY ROESY (Efficient Adiabatic SYmmetrized ROESY), which yields reliable intramolecular distances without a sample-specific setup.

Naturally catalytic: The cinchonidine- and cinchonine-derived bifunctional thiourea organocatalysts 1 a and 1 g (see picture) have been applied in the asymmetric hydrophosphonylation of aromatic and heteroaromatic α-ketoesters for the first time, obtaining S and R products in high yields with good to excellent enantioselectivities (up to 91 % ee).

Ferrocene or ruthenocene? Computational (DFT) methods predicted a metal-dependent photochemistry for metallocenyl–chromium(0)–carbene complexes (see scheme). These theoretical predictions are fully confirmed by the experimental results.

Maiden voyage: New arsenic-, antimony- and bismuth-donor reagents (1 b–d) are used in a one-pot synthesis of cyclic arsanes, stibanes and bismutanes through a procedure in which the simultaneous formation of three CAs, CSb or CBi bonds is achieved. At the end of the reaction, the element-donor reagent can be easily re-formed “in situ” and recycled, as in a catalytic process.

From wood biochemistry to metabologeography: Non-targeted ultra-high-resolution Fourier transform ion cyclotron resonance mass spectroscopy (FTICR-MS) and NMR spectroscopy analyses show that broad chemical spaces particular to a given oak species in a given forest can manifest themselves in the composition of barrels and related barrel-aged wines (see graphic).

Hollow micropipes with parallelogrammatic shape can be obtained by simple evaporation of a solution of C₁₂ or C₁₄ alkoxy-2-trifluoromethylbenzamide on a substrate. A study on analogues with various alkyl chain lengths revealed that an evaporation-induced self-templated polymorphic transition, in which one polymorph acts as a template and the other as a negative replica, is responsible for the formation of hollow three-dimensional crystalline structures (see picture for schematic mechanism and SEM image of a pipe).

Borylene or substituted borane, metal–metal bond or none? For the borylene-bridged title complex and its analogues with bridging amino-borylene, methylene and vinylidene ligands, the second question gets a clear “no” from QTAIM and ELF analyses. But the first question depends, in a striking manner, on the computational method, due to an interesting bifurcation between two different bonding situations (top: BHLYP, bottom: BLYP plots).

^99mTc does it in water! The reaction of [^99mTcO₄]⁻ in water with phosphine-derivatised resins and triazacyclononane-based ligands gave the Tc^VII complexes [^99mTcO₃(N³)]⁺. In water, these complexes undergo [3+2] cycloadditions with alkenes to form Tc^V glycolato complexes (an example is shown here). Conjugation of alkenes to biomolecules thereby enables a direct labelling strategy, which is ligand- rather than metal-centred.

Bringing in the replacements: Donor- and acceptor-substituted phenanthrenyl pairs as natural-base-pair replacements stabilize DNA duplexes and show interesting fluorescence behavior that varies depending on the substituent at the phenanthrene chromophore.

N₂to ammonia: The differences in reactivity etween Mo[{RNCH₂CH₂}₃N], R=3,5-(2,4,6-iPr₃C₆H₂)₂C₆H₃, which is capable of converting N₂ to ammonia catalytically, and Mo[N(R)Ar]₃ (R=tBu, Ar=3,5-C₆H₃Me₂), which cannot, were explored by using density functional theory.

Rich smectic mesomorphism, including uncommon crystal smectic T phases, is exhibited by ionic liquid crystals based on N-alkyl-N-methylpyrrolidinium cations and various counteranions, including a new type of uranium-containing metallomesogens (e.g., see picture; C grey, Br green, N blue, O red, U yellow, H omitted). The U-containing mesogens are photoluminescent when dissolved in an ionic liquid, and the Eu^III-based liquid crystal shows intense red photoluminescence with high colour purity.

Silicon networking: The vacuum-UV (VUV)-induced conversion of polyorganosilazanes into methyl-Si-O-Si networks was studied using 172, 185, and 222 nm UV light (see graphic). TOF-SIMS, XPS, and FTIR measurements as well as kinetic investigations were carried out to elucidate the occurring chemical reactions, such as SiNH and SiCH₃ degradation.

Go bio! We report here the synthesis and cell-proliferation studies of the first derivatives of the breast cancer drug tamoxifen in which an organometallic moiety replaces the antiestrogenic side chain (see graphic). Structure–activity relationship studies show that the compound possessing two phenol groups and a carbonyl adjacent to the ferrocene has the best receptor-binding and cytotoxic properties.

Consecutive construction: Diastereoselective Claisen rearrangements of allyl vinyl ethers with a sulfoxide at C-5 allow for the creation of up to two consecutive asymmetric centers and a new vinyl sulfoxide (see scheme).

Glycoferrocenes as sensors: Ferrocene–carbohydrate conjugates with different tethers and sugars were synthesised by two convenient methods. The electrochemical behaviour of these compounds was investigated, as well as their complex formation with β-cyclodextrin (see figure) by NMR, ITC, CV and DPV experiments.

In a pinch: Chiral pincer complexes [RuCl(CNN)(Josiphos)] (see figure) are easily obtained by a one-pot reaction of [RuCl₂(PPh₃)₃] with 1-[1-(dicyclohexylphosphano)ethyl]-2-(diarylphosphano)ferrocene (Josiphos) and racemic HCNN pincer ligands, promoted by acetic acid. These complexes are highly active and productive catalysts for the asymmetric hydrogenation and transfer hydrogenation of alkyl aryl ketones.

POMs to nanoPOMs: Two reduced polyoxometalates (POMs), one of which adopts a unique cyclohexane-like ring arrangement, are presented. The ring can be used as a precursor to POMs that incorporate organic ligands. Two applications of the redox properties of these species, namely, as reductants for the synthesis of Pd and Pt nanoparticles (see picture) and as precursors for the formation of films electrodeposited on glassy carbon are also shown.

On the face of it, the (010) facet of nanostructured MoO₃ is highly catalytically active and selective for the benzylation of various arenes with substituted benzyl alcohol. The reaction mechanism is discussed based on results from thermal, spectroscopic, and electronic techniques.

Molecular antennae: A series of dendrimeric compounds bearing pyrene units synthesized through the Huisgen reaction afford light-harvesting antennae based on the formation of intramolecular excimers (see picture). Three very efficient energy-transfer multi-emissive systems are obtained, one of which shows interesting, well-balanced emissions in deep-blue, blue-green, and red.

New electrolytes and lubricants: Cyclic sulfonium-based ionic liquids have been synthesized and characterized. Their physicochemical and electrochemical properties suggest their potential application as novel lubricants and electrolytes. The picture shows the structure of a representative cyclic sulfonium-based salt.

A glassy carbon electrode (GCE) is modified with a composite of single-walled carbon nanotubes (SWNTs) and hematin, prepared in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]; see picture). Such functionalization accelerates electron transfer through a synergic effect, and the electrocatalytic activity toward trichloroacetic acid allows the construction of a biosensor.

A mechanism shift that depends on the position of the cyano group occurs in the reductive cleavage of the cyanobenzyl chloride (CBC) isomers in DMF. Whereas m-CBC is reduced along a two-step pathway (dotted curve), o- and p-CBC reduction follow a concerted pathway via a single transition state (full curve). The reason is that electronic coupling between the diabatic states of the products (magnified) eliminates the cleavage barrier for the para and ortho anion radicals. An intermediate anion radical only persists in the case of m-CBC.

Cutting deep into CN bonds: A highly efficient benzylic and allylic alkylation of protic carbon and sulfur nucleophiles with sulfonamides has been developed through ZnCl₂-TMSCl-catalyzed cleavage of sp³ CN bonds at room temperature (see scheme).