Angewandte Chemie International Edition

Molecular mousetraps are an unprecedented class of host–guest reagents. In the example shown in the cover picture, 18-crown-6 ether is utilized as the “bait” to attract target molecules with a protonated primary amine functional group. Appropriate activation of the noncovalent complex springs the diazo “trap”, which leads to covalent attachment of the two molecules depicted in the reaction scheme. The research is detailed in the Communication by J. L. Beauchamp, B. M. Stoltz et al. on page 1012 ff.

A preparative challenge in inorganic solid-state synthesis is to control the morphology of the arising products, for example, of vaterite microsponges (see picture). An important breakthrough in this area has now been achieved with the preparation of microcrystalline Möbius strips and rings from niobium selenide. The synthesis was achieved by a versatile combination of chemical transport reactions and templating techniques.

Simple, direct, and highly enantioselective α-amination of carbonyl compounds 1 with azodicarboxylates 2 no longer requires prior enolization of the substrate. The “magic” small-organic-molecule catalyst for this reaction in dichloromethane at room temperature is once again L-proline (3).

Shapely structured inorganic materials of diverse morphologies and compositions are nowadays obtainable through the transcription of organic templates (see picture). This review gives an overview of the various kinds of templates, precursors, and methods that have been employed for this purpose, as well as the diversity of inorganic materials that have been obtained.

A planar C₁₆B₈octagonal macrocycle that incorporates four identical metallacarborane units, linked by four diethynyl chains, has been prepared from a monomeric cobaltacarborane through a designed multistep synthesis (see picture). The air-stable molecule undergoes stepwise electrochemical reduction in THF solution to generate mono-, di-, and tetraanions, with the cyclic and square-wave voltammetric data indicating significant electron delocalization in the ring system.

Insertion of a symmetric metal complex, [Cr^III(5,5′-tBu-salophen)]⁺ (H₂salophen=N,N′-bis(salicylidene)-1,2-phenylenediamine), into the active site of apomyoglobin is demonstrated (see picture). The metal ion and the ligand structure are very important factors that influence the binding affinity of the metal complex with the myoglobin (Mb) cavity. Semisynthetic metalloenzymes can catalyze enantioselective sulfoxidation by using the chiral protein cavity.

A stack with a twist is formed when a thymidine bolaamphiphile (green rod with red ends in the scheme) is allowed to interact with strands of oligoadenylic acid (purple chain with yellow pentagons) in aqueous solution. Complementary A–T hydrogen bonding leads to nanofibers having a DNA-like double helix.

The covalent linking of noncovalently bound host–guest complexes in the gas phase is achieved by the formation of a highly reactive carbene from the host molecule, which is generated by collision-activated dissociation. Possible mechanisms for the resulting intermolecular reactions are explored by theory and experiment.

A lanthanide/organic radical based molecular magnet (T_c=3.5 K) has been prepared from a reaction of GdCl₃⋅6 H₂O with Li[TCNQ] (TCNQ=7,7,8,8-tetracyanoquinodimethane). The title compound was structurally characterized by single-crystal X-ray diffraction and contains distinct anionic and cationic (see picture) networks containing Gd, TCNQ, and H₂O in different ratios.

Activation of methane by metal peroxides: Calcium peroxide serves as an effective radical initiator in the liquid-phase sulfonation of methane to methansulfonic acid (MSA) by SO₃ [Eq. (1)]. Under the best reaction conditions a 91 % conversion of SO₃ to MSA was achieved.

The kinetic anomeric effect has been used to control both α and β stereoselectivity in glycosidation reactions. Depending on the restricted conformation ⁴C₁ or ¹C₄ of the substrate, the anomeric α (1→2) or β product (3→4) was obtained highly stereoselectively from the Lewis acid promoted anomeric allylation with allyltrimethylsilane (TIPS=triisopropylsilyl).

Sterically hindered pentacoordinate tert-butylsiliconium halide complexes undergo methyl halide elimination. The products have one covalent and one dative NSi bond, both in the unprecedented equatorial position. A complete pseudorotation coordinate is demonstrated with suitable crystal structures.

High catalytic performance of the electrogenerated amine oxidase mimic 3,4-iminoquinone 1_ox is observed under metal-free conditions in the chemoselective oxidation reaction of unactivated primary aliphatic amines.

Excellent response to visible light is shown by the [Fe^II(bpy)₃]–amberlite photocatalyst, which can effectively activate molecular oxygen in such a way as to put us one giant step nearer to our goal—the development of the ultimate green technology for decontamination [Eq. (1)].

Catalytic asymmetric addition of vinylic halides and triflates to aldehydes, with useful levels of stereoinduction, has been achieved for the first time using the salen-type ligand (S,S)-5 (see scheme; PMB=para-methoxybenzyl), which contains the novel endo,endo-2,5-diamino norbornane building block. This asymmetric Nozaki–Hiyama–Kishi reaction leads to the coupling of various halides and aldehydes with high yields and enantioselectivities (up to 92 % ee).

Readily available starting materials and high selectivity: These are two appealing features of the phosphane-catalyzed carbon–phosphorus ylide reaction described. Bromide, acetate, or tert-butyl carbonate derivatives of adducts formed by the Morita–Baylis–Hillman reaction react with PPh₃ to form an allylic ylide. Phosphane-catalyzed annulation of the ylides with electron-deficient alkenes results in the facile construction of cyclopentenes [Eq. (1)]. X=Br, OAc, OBoc; E=CO₂Et.

Sc^IIor mixed oxidation state Sc^III/Sc^I? Reduction of the homoleptic Sc^III complex [Sc(P₃C₂tBu₂)₃] allows access to the subvalent [{Sc(P₃C₂tBu₂)₂}₂] complex (see picture), in which the metal centers are formally bivalent. DFT calculations support fomulation of the reduced species as a mixed oxidation state Sc^III/Sc^I complex.

A mild, green method for enantioselective kinetic resolution of secondary alcohols has been developed using Mn(salen) complexes as catalysts in water. Up to 97.8 % ee was attained. PTC=phase-transfer catalyst.

The tetracyclo[4.2.0.0^2,4.0^3,8] oct-7-ylium cation is the protonation product of cubane (1) in the gas phase according to ab initio and DFT calculations. At the G2(MP2) level, the calculated gas-phase basicity of 1 is about 60 kcal mol⁻¹ larger than that determined experimentally. The experimental thermodynamics are consistent with fast deprotonation of 2 to give cuneane (3).

Gold(I) Phosphanyl Complexes, such as [Au(PR₂)]_n, have been known for more than 25 years. However, the solid-state structure of such complexes, as well as their nature in solution, has remained somewhat of a mystery. The figure displays the cyclic and polymeric forms that are possible (L=endgroup). The structures of the complexes, and the occurrence of Au⋅⋅⋅Au interactions are discussed.

The exchange of the short and long diagonal of the B₄ diamond of 1 is the simplest variant to date of the diamond–square–diamond rearrangement, which plays a central role in the isomerization of polyhedral boranes, carboranes, and metallaboranes. Compound 2, which is readily accessible from 1, is the first derivative of pentaborane(7).

Nucleophilic addition of fluoride ions at the carbonyl carbon atom in (CF₃)₃BCO in liquid sulfur dioxide leads to the formation of the boron acyl fluoride ion [(CF₃)₃BC(O)F]⁻ (see structural formula), the first example of a compound with a BC(O)F group and an anionic acyl fluoride.

Aryl chlorides are suitable substrates for the Sonogashira coupling! By using the versatile catalyst system Na₂[PdCl₄]/PR₃/CuI (PR₃=(1-Ad)₂PBn, PtBu₃), the Sonogashira coupling [Eq. (a)] of aryl chlorides with alkynes generates excellent yields of the corresponding disubstituted aryl alkynes.

Building bridges: Fumed colloidal silica can be dissolved in alkaline aqueous solutions of the open-chain sugar alcohols mannitol, xylitol, and threitol. These polyols are able to form six-coordinate silicon complexes that are stabilized by intramolecular hydrogen bonds. The prototypical core is shown (yellow bars: the intramolecular H bonds).