To be or not to be (a bond, that is)? Recent progress in X-ray charge-density analysis is discussed with emphasis on the characterization of unusual bonding situations, such as the recently reported CC “bonding” interaction in a [1.1.1]propellane (see structure).

Ketene esterification after 100 years: In the latest advance in the esterification of ketenes, Schaefer and Fu described the catalytic asymmetric conversion of 2-tolyl(ethyl)ketene (1) and diphenylacetaldehyde to give the enol ester 2 in 99 % yield and 98 % ee (see scheme).

Ligands scoot together: Noncovalent attractive interactions between ligands in the coordination sphere of a metal center lead to a situation typical for complexes with classical bidentate ligands (see picture). In tests with catalyzed reactions these self-assembled systems gave results comparable to those obtained with complexes having classical bidentate ligands.

Increasing genomic information together with new tools in molecular microbiology have led to powerful and rational applications in natural product research (see picture). Today, it is possible to produce novel and altered secondary metabolites with biological activity.

Room for one more? The structures of nanosized Pd₅₂ and Pd₆₆ clusters that are based upon a common Pd₃₈ vertex-truncated ν-octahedral kernel have been determined. The 45 CO ligands in the Pd₆₆ cluster (see core structure), [Pd₆₆(CO)₄₅(PEt₃)₁₆], are described in terms of one extra and 44 normal ligands, two of which undergo rearrangement to accommodate the 45th CO ligand without causing any substantial changes to the architecture of the metal core.

Pretty as a picture: The printing of highly complex graded images with two different species (see picture) has been developed through the use of double-barreled pipettes. This method of submicron deposition of biomolecules eliminates registry problems that are inherent to other deposition techniques.

Complex nanomolar inhibitors in one pot: Aminoglycoside–coenzyme A derivatives were prepared through an efficient regioselective 6′-N modification of aminoglycosides (see scheme). These bisubstrates show tight-binding competitive inhibition of aminoglycoside 6′-N-acetyltransferase, an enzyme involved in antibiotic resistance.

Catalyst sandwich: An efficient and sensitive high-throughput-screening method that uses sandwich immunoassays was developed and applied to the Sonogashira reaction. This new method is amenable to coupling reactions and allows the screening of more than 1000 catalyst samples per day.

Cyanide clusters [Re₁₂CS₁₇(CN)₆]ⁿ⁻ (n=8 or 6), which may be used to form polymeric material, have been prepared by treating ReS₂ with molten KCN at 750 °C. The cluster unit comprises two {Re₆} octahedra connected by three μ₂-S bridges and one interstitial μ₆-C atom (see picture).

A combination of techniques (Mössbauer and X-ray absorption spectroscopy, H₂¹⁸O exchange experiments, and DFT calculations) has shown that the reaction of [Fe(H₂O)₆]²⁺ with ozone generates [(H₂O)₅Fe^IVO]²⁺ (see calculated structure). The oxidation of selected substrates with [(H₂O)₅Fe^IVO]²⁺ yields unique products that are different from those generated in the Fenton reaction or derived from HO^. radicals.

H Box: The clusters [Rh₆(PR₃)₆H₁₂][BAr^F₄]₂ (R=cyclohexyl, iPr; see scheme, pink Rh, orange P) reversibly take up two molecules of H₂ under ambient conditions (1 atm H₂, 298 K) to give discrete octahedral clusters surrounded by 16 hydride ligands.

Crystals with broad robust channels are rare, especially if self-assembled without the aid of metal ions. Three such crystals were prepared based on a common steroid motif. The channels formed are chiral, directional, aligned, and wide enough (>1 nm) to accept a variety of guests (see picture; red: oxygen, blue: nitrogen, green: fluorine).

Microporous: Chiral metal complexes as templates under solvothermal conditions resulted in two novel germanates Ni@Ge₁₄O₂₄(OH)₃⋅2 Ni(L)₃ (L=ethylenediamine, 1,2-diaminopropane). The chiral Ni@Ge₁₄O₂₄(OH)₃ cluster motifs have an unprecedented trigonal-bipyramidal Ni@Ge₅ core with NiGe bonds and are linked to each other to form a 3D germanate framework containing 24-ring channels (see picture).

A homogeneous catalytic complex is tagged with two ferrocenyl groups to control its solubility properties by reversible switching between its neutral and dicationic states (see scheme). This approach is carried out on an olefin-metathesis catalyst and is shown to effectively switch its catalytic activity on and off; furthermore, efficient separation of the catalyst from the reaction products and subsequent recycling of the catalyst is possible.

Getting a grip on the flu: A mechanism-based probe, 1, for neuraminidase was developed. It is capable of forming a biotinylated adduct with neuraminidase (NA) from Arthrobacter ureafaciens. It also displays an inhibitory effect on a number of NA activities. ELISA experiments successfully demonstrated that influenza viruses can be selectively captured with this probe.

An auraoxetane, obtained from the reaction of norbornene with a gold(III) oxo complex, has been isolated and fully characterized (see structure). Action of the olefin leads to elimination of the epoxide from the auraoxetane.

The isolation and intramolecular cyclization of (S)-(1-alkynyl)isothiouronium and (S)-(1-alkynyl)thiobenzimidonium salts suggest the mechanism for the one-pot synthesis of 2,4-disubstituted thiazoles (see scheme; Ms=methanesulfonyl): Michael addition of sulfur nucleophiles to hypervalent iodanes followed by the 1,2-rearrangement of sulfenyl groups in the resulting alkylidene carbenes.

Interaction over a distance: Long-range antiferromagnetic interactions between distant copper(II) and silver(II) ions are observed only for triply and singly linked diporphyrins with at least one β–β bond, which underscores the critical importance of this direct bond for antiferromagnetic coupling. These results can be qualitatively accounted for in terms of the spin distribution of copper(II) and silver(II) porphyrins (see picture).

A rational building-block approach was employed to construct organometallic/polyoxometalate (POM) hybrids in which POM clusters and transition-metal complexes are linked by a π-conjugated bridge. The synthetic strategy for molecular and polymeric hybrids—POM functionalization with iodo-bearing groups, attachment of a terpyridine-type ligand, and metal coordination—is shown schematically in the picture.

Mixed-ion and electron-conducting perovskite membranes are used to produce oxygen-enriched air (see picture). These membranes are thermally and mechanically stable at high temperatures (>875 °C) over a long period of time, thus making them suitable for industrial processes. Oxygen concentrations of the enriched air typically reach 30–50 vol %.

To twist or not to twist? A ditopic ligand, L¹, that contains a potentially tetradentate pyridyl–thiazole ligand chain and a “external” crown ether unit is presented. Reaction of L¹ with Cu⁺ or Zn²⁺ ions results in the formation of a dinuclear double helicate [Cu₂(L¹)₂]²⁺ or a mononuclear [ZnL¹]²⁺ species. This ditopic system changes its preference for Cu⁺ or Zn²⁺ ions on the inclusion of s-block-metal ions at the crown ether binding site (e.g., Sr²⁺ ions as shown in the scheme).

An air-stable, heterogeneous, and recyclable catalyst composed of palladium nanoparticles entrapped in aluminum hydroxide was applied to a highly selective α alkylation. A wide range of aliphatic and aromatic ketones and primary alcohols were coupled to prepare enones in an O₂ atmosphere and ketones in an argon atmosphere (see scheme).

A highly specific and catalytic oxidation of water occurs when using a dinuclear Mn complex of a mononegative carboxylate-containing pentadentate ligand (see scheme). Isotope-labeling experiments coupled with membrane inlet mass spectrometry show that one oxygen atom in the evolved O₂ molecule is derived from water and the other from the oxidant.

A europium complex capable of selectively binding zinc (see picture) has been developed as a new paramagnetic chemical exchange saturation transfer (PARACEST) imaging agent for use in magnetic resonance imaging (MRI). A hydroxide group on the bound Zn ion increases the rate of water exchange on the Eu ion.

Stereochemical alchemy! Racemic allyl β-ketoesters allow the regiocontrolled formation of enolates, where the same catalyst is intimately involved in both the stereoablative (CC bond-breaking) and stereoselective (CC bond-forming) steps. This mechanistic and practical insight led to the formation of multiple quaternary carbon stereocenters in a single cascade reaction (see scheme).

Structural transition from type I to type II is accompanied by a large increase in lattice constant a in CH₄+C₂H₆ clathrate hydrates (see picture). In contrast, the lattice constants of CH₄+CO₂ clathrate hydrates are independent of composition. Data for a natural gas hydrate from the sediments of Lake Baikal are also consistent with these trends.

Versatile intermediates for the synthesis of N-aryl-α-amino acids and N,N-disubstituted 1,2-diamines can now be synthesized with high efficiency by the ruthenium-catalyzed oxidative cyanation of tertiary amines. The use of hydrogen peroxide as an oxidant in the presence of NaCN/AcOH or HCN provides the corresponding α-aminonitriles (see reaction).

Promising building blocks: High-density radially-oriented amorphous silica nanowires standing on a single-crystal Si nanocore were synthesized by simple thermal evaporation of silicon with tin as catalyst. The growth process (see schematic picture) appears to involve concurrent vapor–liquid–solid and oxide-assisted growth mechanisms. Scanning electron micrographs corresponding to 1 and 2 are also shown.

Two tags are better than one: Sixteen individual stereoisomers of murisolin (see scheme) are synthesized together and isolated in pure form with the aid of a double-separation tagging procedure. A strategy for solution-phase stereoisomer synthesis based on double-separation tagging and double demixing is implemented with fluoroalkyl and oligoethylene glycol (OEG, (OCH₂CH₂)_nOCH₃) tags.

When excess charge is deposited on thymine and uracil by resonant attachment of low-energy electrons (0–3 eV), H atoms are cleaved exclusively from the N positions. This bond selectivity can be made site selective (N1 vs. N3 position) by properly tuning the electron energy. This conclusion was drawn from experiments with methylated thymine and uracil (see picture) in crossed beam experiments.

Optical control of the photo- and electrochemiluminescence of a brightly fluorescent reporter group is possible by switching between the photochromic units of dyads 1 a and 1 b. Irradiation, that is, writing in information, with UV light converts the highly luminescent dihydroazulene 1 a into the weakly emissive vinylheptafulvene 1 b. Readout of the system can be performed by either electrochemically generated or photogenerated luminescence.

Out of thin air, a rhodium complex converts molecular oxygen into hydrogen peroxide, bis(trimethylsilyl) peroxide, and methyl hydroperoxide. Intermediate η¹-hydroperoxo and η¹-silylperoxo, and η¹-methylperoxo complexes have been isolated. Another η¹-methylperoxo (see picture) and an η¹-hydroperoxo complex have been characterized by X-ray crystallography.

In one go: (Hetero)aryl iodides, alkynes, carbon monoxide, and amidines can be assembled in a consecutive four-component reaction to give pyrimidines by a sequence of carbonylative alkynylation and cyclocondensation. Carbonylative alkynylation also is the key step in the two-step syntheses of meridianins and meridianin derivatives.

Polyhedral Al halides: Four halogen atoms directly coordinated to an Al₁₂ icosahedron in two structurally characterized Al₂₀ clusters indicate the mechanism of formation of Al₂₂X₂₀ subhalides. No Al atom is located in the center of the icosahedron in either of these icosahedral compounds!