Angewandte Chemie International Edition

Molecular and crystal engineering rendered high-performance organic thin-film transistors (TFTs) based on a highly electron-poor octachloroperylene diimide (Cl₈-PTCDI). In their Communication on page 740 ff., F. Würthner, Z. Bao, and co-workers report an intriguing supramolecular crystal engineering concept that directs two-dimensional π–π-stacked percolation paths for electron transport and affords TFTs with excellent mobilities and on-to-off current ratios under atmospheric conditions.

From a square to a loop! In their Communication on page 757 ff., S. Yamago et al. describe the first synthesis of [8]cycloparaphenylene, which was achieved in three steps in 25 % overall yield from 4,4′-bis(trimethylstannyl)biphenyl and [PtCl₂(cod)] (cod=1,5-cyclooctadiene) through a square-shaped platinum biphenyl intermediate. [8]cycloparaphenylene shows strong yellow-green fluorescence around 540 nm.

“The most exciting thing about my research is observing unexpected but significantly important results. The biggest problem that scientists face is how to balance curiosity-driven research and applied research …” This and more about Dawei Ma can be found on page 666.

John Wiley & Sons, Hoboken 2008. 470 pp., hardcover € 89.90.—ISBN 978-0470081037

A molecule on a slippery slope: Lineberger et al. finally managed to observe the oxyallyl diradical 1 using negative ion photoelectron spectroscopy. The singlet state of the oxyallyl diradical is lower in energy than the triplet and corresponds to the transition state for ring closure to cyclopropanone 2.

Intriguing scaffolds: Tetraphenylenes with symmetry-breaking substitution have chiral π systems and extraordinarily high barriers for racemization. Their applications as building blocks for chiral materials and as ligands in asymmetric synthesis are hindered by the difficulty in obtaining the chiral tetraphenylene core. Rhodium-catalyzed [2+2+2] cycloadditions of triynes provide an effective alternative synthesis.

A good alternative: The developments in the field of metal-catalyzed α-arylation of carbonyl compounds, such as ketones, esters, amides, dicarbonyl compounds, and nitriles are summarized and dicussed in this Review (see scheme). The focus is primarily on how the substrate range can be broadened through variation of the reaction conditions such as ligands, precatalysts, bases, and solvents.

Linked in? Coassembly of an ABA triblock copolymer with charged end blocks and an oppositely charged polyelectrolyte yields gels that respond to changes in concentration, temperature, ionic strength, pH value, and charge composition. Above the critical gel concentration, the triblock copolymers bridge micelles, forming a sample-spanning transient network of interconnected micelles.

Just a pinch of salt: Small amounts of salts accelerate and direct the mechanochemical construction of metal–organic frameworks (MOFs) from a metal oxide (see scheme; ILAG= ion- and liquid-assisted grinding). The resulting rapid and room-temperature synthesis demonstrates the ability to control mechanosynthesis of metal–organic compounds by templating, as well as the ability to use mechanochemistry to include ionic guests within neutral MOFs.

A nice gathering at the interface: The de novo design and characterization of amphiphilic α/β-peptides, which form ordered two-dimensional assemblies at the air–water interface composed of oligomers in pleated conformation similar to β-sheets of α-peptides, is reported. The positioning of ionic side chains along the backbone can exert a profound effect on the propensity to self-assemble.

O₂balks at extra bulk: The introduction of distal-pocket bulk into the Thermoanaerobacter tengcongensis H-NOX (heme nitric oxide/oxygen) domain caused key changes in the protein structure. Rearrangement of the heme pocket resulted in dramatic differences in O₂-binding kinetics and heme reactivity (see picture).

A valuable cargo: Polysaccharides (β-1,3-glucans) act as a host compound to various nanomaterial cargoes such as single-walled carbon nanotubes. The cargo packed in the host container is transported on the rail (F-actin) by wheels and a molecular motor (myosin) attached to the container (see picture). This artificial system is inspired by a container transportation system based on the motion of vesicles in biological cells.

Sila analogues: The first asymmetric synthesis of silacarboxylic acids with a stereogenic center at the silicon atom has been achieved from chiral nonracemic silanols, without loss of optical purity. Silacarboxylic acids can be converted into their corresponding esters using a Mitsunobu-type reaction.

Low in, high out: Single crystals of a thiomethyl-terminated oligo(phenylene vinylene) exhibit unique photonic properties including strong anisotropic solid-state fluorescence (see depicted optical and fluorescence micrographs; arrows: polarization direction), high quantum yield, large two-photon absorption cross section, and stimulated emission, which make it a candidate for opto-electronic applications such as upconversion lasing.

Split personality: A series of oligoamide-based helix mimetics bind to a complementary helical motif in Islet amyloid polypeptide (IAPP), a protein implicated in the pathology of type II diabetes. These compounds accelerated IAPP amyloid formation under lipid-free conditions, but inhibited it under lipid-catalyzed conditions. hIAPP=human IAPP.

Twisted up: Perchlorination of perylene diimide afforded an exceptionally electron-poor organic semiconductor molecule (see picture; C black, Cl green, O red, N blue, H white) that crystallizes in an ideal brickstone arrangement with close π–π and chlorine–chlorine contacts. Vapor-deposited thin films of this molecule show excellent transistor performance, even in air (μ≈0.8 cm² V⁻¹ s⁻¹, I_on/I_off≈10⁸).

No more double trouble: The competing double-addition pathway was suppressed when chiral scandium(III) and indium(III) complexes were used to catalyze the addition of indoles and other π nucleophiles to N-alkylated and unprotected isatins (see picture). The resulting biologically relevant substituted 3-hydroxy-2-oxindoles were obtained in high yield with high enantioselectivity. Tf=trifluoromethanesulfonyl.

Why not let things go skew-whiff? A rational approach was used to program the self-assembly of a DNA octahedron (see structure; the color gradient indicates the distance from the center of the octahedron). Detailed structural characterization revealed that the assembly of the nanoobjects was stereoselective (a view of a vertex is shown with the skewed cavity that provided a handle for determination of the chirality of the octahedra).

In control: The first asymmetric total synthesis of (+)-itomanallene A (revised structure) has been accomplished starting from commercially available (S)-glycidol in a substrate-controlled fashion. The approach yields α,α′-cis- or α,α′-trans-tetrahydrofuran isomers by intramolecular alkylation with either an amide enolate or a nitrile anion, respectively.

Square goes to loop: A selective synthesis of [8]cycloparaphenylene under mild and neutral reaction conditions was achieved in a small number of steps and in a high yield through the square-shaped platinum biphenyl intermediate 1. Compound 1 is the smallest cycloparaphenylene derivative synthesized to date.

InP Kudos: The molecular mechanism of InP colloidal quantum dot (QD) syntheses was investigated by NMR spectroscopy. Unlike methods for monodisperse PbSe and CdSe, existing InP syntheses result in total depletion of molecular phosphorous species following nucleation, so QD growth is due exclusively to non-molecular ripening. Amines inhibit precursor depletion by solvation (see picture), contrary to previous reports.

Inside story: In situ diffraction observations of the crystallization of metal–organic frameworks (MOFs) constructed from transition-metal ions and carboxylate ligands reveal that while some show classical nucleation-growth kinetics, others are formed via metastable transient phases (see picture).

Soft yet strong: Colloidal hydrogel films, which are constructed using a layer-by-layer polyelectrolyte approach, are easily damaged by mechanical disruption, but can also autonomically heal (see picture). The healing event occurs within seconds once the film has been resolvated. The lability of the coulombic interactions between hydrogel particle and linear polymer plays a direct role in its ability to self-heal.

Palladium catalysts bearing dihydroxyterphenylphosphine ligands (such as 1) are reported for the ortho-selective cross-coupling of Grignard reagents and dihaloarenes. The second hydroxy group onto the terphenylphosphine ligand dramatically improved the catalytic efficiency and expanded the scope of the reaction.

Atom-economical: Unmodified hemi-N,O-acetals are used in a catalytic, highly efficient α-amidoalkylation of a broad range of carbon-centered nucleophiles, including silicon-based components, active methylene derivatives, electron-rich arenes, and even simple ketones (see scheme). The reactions proceed in a highly efficient manner and typically require only 1 mol % of the Lewis superacidic reagent Sn(NTf₂)₄ as the catalyst.

Just mix in water 'n stir: Pd-catalyzed CH activation/cross-couplings can be carried out at room temperature in water/surfactant mixtures. The combination of Pd(OAc)₂ and HBF₄ allowed for reactions of aryl ureas with aryl iodides under very mild conditions, using micellar catalysis (see scheme). This reaction is made possible by use of an in situ generated cationic palladium catalyst.

Jump to it! 2D IR pressure-jump spectroscopy of adsorbed CO can be used to assess the accessibility and location of platinum nanoparticles supported on a zeolite and investigate the behavior of Pt atoms after thermal treatment (activation, catalytic reaction, sintering). Different Pt nanoparticle sintering mechanisms were observed in the mesopores and on the external surface of the ZSM-5 support (see picture; HF=high and LF=low frequency).

Coming clean? Liquid chromatography–ESI tandem mass spectrometry is used to detect 2,6-dichloro-1,4-benzoquinone (see picture) in drinking water treated with chlorine or chloramine.

A rare event: The benzylpalladium amido complex 1 (Ar=napthyl) was used to study the mechanism of an unusual reductive elimination of amines (see scheme). The observed inversion of configuration is proposed to result from dissociation of the amido ligand, followed by nucleophilic attack on the benzylic carbon atom. binap=2,2′-bis(diphenylphosphanyl)-1,1′-binaphthyl, dppf=1,1′-bis(diphenylphosphanyl)ferrocene.

The dimethyl phosphonate hydrophosphonylation of conjugated- and non-conjugated aldehydes into their corresponding α-hydroxy phosphonates was achieved using chiral aluminum–salalen complex 1 (see scheme).

Seeing O: Mn Kβ_2,5 and Kβ′′ X-ray emission spectra arise from transitions from the ligand 2s and 2p shells of the metal complexes to the metal 1s levels. In biological systems, it is difficult to specifically probe the O and N ligands. This spectroscopic technique is used to study the O ligands of the Mn₄Ca cluster that catalyzes photosynthetic water splitting and allows direct detection for the first time of the bridging oxo groups of Mn.

Ruthenium has twice the fun: The synthetic potential of the highly regio- and stereoselective title reaction, which relies on two oxidative cleavage steps promoted by RuCl₃ in combination with NaIO₄ (see example; Bz=benzoyl), was demonstrated with the synthesis of biologically active cis-(2R,3S)-3-hydroxypipecolic acid from D-glucose.

Catalytic specificity of side pockets: Monomolecular reactions with higher activation energies—dehydrogenation of linear alkanes (n-butane: blue) and cracking of branched alkanes (isobutane: green)—show a stronger preference for acid sites located within eight-membered ring (8-MR) side pockets in mordenite, where reactants and transition states can only be partially confined. Partial confinement leads to higher entropies and lower free energies for ion pairs at late monomolecular transition states.

Saturnene has four moons: Reactions of C₆₀ with ternary metal fluorides yielded fluorofullerenes from C₆₀F₂ to C₆₀F₄₈, including elusive saturnene, C₆₀F₂₀, which has now been characterized by X-ray crystallography. Four benzene molecules “hover” over this D_5d molecule at the corners of a square inscribed in the idealized body-centered-cubic unit cell (see structure; F yellow). The tight unit-cell packing explains the very low solubility of saturnene.