Chemistry - A European Journal

Here, Newton's cradle demonstrates the concept of alkali-metal-mediated manganation. On its own as part of a conventional organomanganese compound Mn^II cannot usually directly metalate arene molecules. However, pushed by sodium in the form of a sodium manganate reagent, Mn^II can form direct MnC(arene) bonds selectively knocking off a hydrogen atom and forming a sodium–manganese–arene complex. In their Full Paper on page 65 ff., R. E. Mulvey et al. discuss the first examples of direct manganation of functionalised arenes.

Chemistry reloaded: The construction of a variety of molecular devices and machines powered by chemical, photochemical, and electrochemical inputs and the novel conceptual interpretation of known classes of chemical reactions have opened new scenarios on the potentiality of chemistry for energy- and signal-processing at the molecular level.

Total synthesis of carbohydrates: Recent developments of several organocatalyzed aldol methodologies for the total synthesis of carbohydrates to obtain configurationally defined products are discussed.

Branching out: “Click” dendrimers containing 1,2,3-triazolyl ligands (an example of which is shown here) that coordinate to Pd^II(OAc)₂ have been synthesized and reduction with methanol gives precise dendrimer-stabilized Pd nanoparticles that show high efficiency and selectivity in catalytic olefinic hydrogenation.

Direct approach: Circumventing the need for indirect metathetical syntheses, the first direct manganation(II) reactions of functionalised arenes using the sodium–Mn^II base [(tmeda)Na(tmp)(R)Mn(tmp)] (TMEDA=N,N,N′,N′-tetramethylethylenediamine, TMP=2,2,6,6-tetramethylpiperidide, R=CH₂SiMe₃) are reported together with the conversion of the crystallographically-characterised ortho-manganated intermediates (see figure) thus obtained into unsymmetrical biaryls through Pd-catalysed cross-coupling reactions with iodobenzene.

The platinum twist: These platinum complexes are accessed by reactions of trans,trans-[(C₆F₅){(p-tol₃P)₂}Pt(CC)_nPt{(Pp-tol₃)₂}(C₆F₅)] and Ar₂P(CH₂)_mPAr₂ (m/2n/Ar=8/6/p-tol, 10/6/Ph, 11/6/Ph, 12/6/Ph, 14/6/p-tol, 14/6/ p-C₆H₄-tBu, 8/4/Ph, 8/4/p-tol). Those with n=3 crystallize with coplanar endgroups in the limiting structures A (m=14; double-helical) and B (m=10, 11; non-helical); those with n=2 have endgroup–endgroup interactions that prohibit coplanarity, and exhibit dissymmetric non-helical conformations in solution.

Synergistic coordination between isonicotinate (IN) and μ₃-O ligands, as well as IN and μ₄-I ligands under hydrothermal conditions results in two networks of {Dy₁₈} and {Cu₂₄} wheels, built from unusual [Ln₃(μ₃-O)] and [Cu₄(μ₄-I)] cluster cores, respectively, which are stacked, form two kinds of hexagonal channels that interpenetrate each other (see picture) and are further pillared by IN ligands to produce a series of sandwich frameworks: [Ln₆(μ₃-O)₂](IN)₁₈[Cu₈(μ₄-I)₂(μ₂-I)₃]⋅H₃O (Ln: Y, Nd, Dy Gd, Sm, Eu, Tb).

Head-to-tail: A double calix[6]arene with the structure of an asymmetric oriented nanotube, about 2.6 nm long and 1.6 nm wide, can act as a wheel and forms a pseudorotaxane with a 4,4′-bipyridinium (viologen) salt (see picture). The properties of this complex were investigated in solution by UV/Vis absorption spectroscopy and voltammetric methods. In the solid state, the molecule initiates extended oriented tubular structures that give rise to a system of parallel sandwiched nanotubes in the lattice.

C₇₀fullerene clectrochemistry: An electrochemical and DFT study of 17 C₇₀(CF₃)_n derivatives (see graphic) has shown that E_1/2 values for isomers of a given composition can vary by nearly 0.5 V.

Discover your origins! The mechanism for the α-functionalisation of aldehydes (see scheme) has been investigated by computational methods. This has led to a new insight into the origin of the stereoselectivity.

Optically active bisphosphonates were obtained in high yields and enantioselectivities of up to >99 % ee by cinchona alkaloids-catalyzed Michael-type addition of β-ketoesters to ethylidenebisphosphonate esters (see scheme). Further reactions of Michael adducts to the corresponding bisphosphonic acids or vinyl phosphonates have also successfully been performed with conservation of optical purity.

Down-sized channels: The immobilization of β-CD monolayers inside microchannels is described. These microchips are designed such that they can be used for the selective immobilization of proteins in different channels. One example is the alternating fashion in which two fluorescently labeled antibodies are immobilized in the chip (see figure).

Recognition of protein surfaces: Calorimetric investigation revealed that nanoparticles (NPs) bearing enantiomeric and diastereoisomeric amino acids/dipeptides (see graphic) display distinctly different binding affinities toward protein targets. This isomeric control of protein recognition has been demonstrated to arise from the noncompensatory enthalpy and entropy contributions in the complex formation.

Prot(e)o-types: Mesoporous silicates with cyano functional groups for accommodating trypsin have been proposed as a nanopore-based bioreactor to favor highly efficient protein digestion inside the mesochannels (see graphic).

Two is better than one! [Cu(NHC)₂]X complexes are easily prepared and are efficient precatalysts for the hydrosilylation of ketones. Relevant steps of the catalytic mechanism have also been demonstrated (see scheme).

En-lightening: New tetrapyrrole chromophores for light-energy conversion, namely, free-base corroles are connected to perylene bisimide to form stable dyads that display photoinduced electron transfer resulting in efficient formation of charge-separated states (see picture).

A new proflavine-based intercalator and its Zn^II complex form DNA adducts according to intercalative and groove-binding processes, as shown by means of spectroscopic methods and stopped-flow measurements. Molecular modelling studies support both binding processes and provide evidence for the influence of NH⁺⋅⋅⋅O interactions between the protonated acridine nitrogen and the oxygen atoms of the polyanion; this promotes the formation of DNA adducts in which the intercalator penetrates perpendicularly to the base pair hydrogen bonds (see picture).

Three previously unknown polymorphs of phenyl carbamate are characterized. The phase transformation from form I to form II is rapid by both solution-mediated and solid-state transformation processes. Through comparison of their structures it is possible to propose a mechanism for the transformation.

Prepare for the unexpected! Unexpected site-selective cycloadditions of triply linked diporphyrins gave a triply linked porphyrin–chlorin hybrid and a bischlorin as respective symmetry-allowed [4+2] and symmetry-forbidden [4+4] cycloadducts (see scheme).

Even nanoparticles need gold: The mechanism of alcohol oxidation by gold nanoparticles supported on nanoparticulated ceria, a general catalyst for aerobic alcohol oxidation (see scheme), has hydride transfer as the rate-determining step.

Copper crowns: The 12-MC-6 copper/fluoro metallacrown shown here binds NH₄⁺ at the center of its Cu₆F₆ ring, but complexes MeNH₃⁺ and amino acid guests in bowl-shaped cavities above and below it.

The Lewis acid–Lewis base complexation chemistry of SiCl₄ and HMPA has been studied in solution and the solid state. The cationic complex 3 HMPA⋅ SiCl₃⁺ HCl₂⁻ (see figure) has been structurally characterized for the first time.

Sticking together like glue! Interesting self-assembly behavior of hexa-peri-hexabenzocoronene derivatives was observed both in solution and the bulk state, owing to hydrogen bonding and π-stacking interactions. Depending on the nature of hydrogen-bonding functionality, some molecules gel organic solvents, which leads to the formation of fluorescent organogels (see figure).

The donor moiety of the 1,6-dithiapyrene–C₆₀ dyad (see graphic) is aromatic in its ground state, but not in the radical ion form. Nonetheless the photogenerated charge-separated state has a remarkably long lifetime for such closely-spaced donor–acceptor systems.

Sequence switching: An azamacrocyclic ligand (L), with two anthracene fragments connected through polyamine bridges, behaves as a fluorescent molecular switch driven by the input sequence of metal cations. Sequential Zn²⁺→Cd²⁺ addition results in excimer emission, whereas the reverse sequence does not (see picture).

Mechanisms compete for palladium! The mechanism of the palladium-catalysed [3+2] cycloaddition of alk-5-ynylidenecyclopropanes to alkynes has been studied at the DFT level (see scheme). The most plausible reaction pathway involves four steps. Alkynes substituted with an ester group follow a different mechanism in accord with the experimental observations.

A versatile ligand: The cluster compound [Cp₂Mo₂(CO)₄(μ,η²-P₂)] reacts with a variety of group 11 metal salts to yield monomeric or dimeric complexes. The dicationic species that are invariably obtained, if salts of weakly coordinating anions are employed, display unexpected dynamic behaviour in solution (see illustration), which could be elucidated with the help of DFT calculations.

A new silane/imido coupling mechanism is proposed to account for the reactions of hydrosilanes with the d² imido complexes [Nb(Cp)(NR)(PR′₃)₂]. The initially formed intermediate A, has a penta-coordinate silicon centre and an agostic SiH⋅⋅⋅Nb interaction, that rearranges in the example silyl hydride B shown here (R′₃=Me₃, PhMe₂; R′′₂=Cl₂)

The enantioselective synthesis of 2,4-dimethyl-1-penten-1,5-ylidene derivatives has been developed and involves the combined use of Zr-catalyzed methylalumination of alkynes (ZMA) and Zr-catalyzed asymmetric carboalumination of alkenes (ZACA; see scheme).

Getting to the core of the matter: Disorder of silver atoms and high cation mobility are commonly observed and are closely coupled features in silver chalcogenides. In the model compound [Ag₂₈S₂₆(P(O)PhOMe)₁₂(PPh₃)₁₂] this disorder of Ag atoms was observed in the crystal structure and investigated by density functional calculations (see figure).

Carbocyclization reactions: Three-, five-, six-, and seven-membered rings are easily available in a diastereoselective manner from Fischer carbene complexes and 4-unsubstituted 1-amino-1,3-dienes (see scheme). The nature of the substituent of the carbene complex is crucial to lead the reaction to each type of carbocycle.

Unusual structures: A series of phosphine–borane adducts R₃PB(C₆F₅)₃ features unconventional eclipsed structures (an example is shown here). A detailed DFT analysis has revealed a combination of secondary interactions to account for this remarkable structural behaviour.

Reaction mechanisms: The results of density functional theory (B3LYP) and ab initio (QCISD and CCSD) calculations were used to understand the mechanism of aromatic hydroxylation (see scheme) by a transient terminal copper–oxo complex. Two pathways, a stepwise and a concerted reaction, were considered for the hydroxylation process. The results reveal a clear preference for the concerted pathway, leading to the ortho-selectively hydroxylated product.

A successful strategy for the synthesis of novel functional star- and eight-shaped copolyesters (see figure) is described. It relies on the combination of controlled ring-expansion polymerization of lactones, macrocyclization by the intramolecular photo-cross-linking of pendant unsaturations in the very close vicinity of the propagating sites, and “click” chemistry (Huisgen's [2+3] cycloaddition).

Coupling mechanism brought to light: Picosecond transient species formed by photoexcitation of [Ru(dppz)(tap)₂]²⁺ intercalated into [poly(dG-dC)]₂ (illustrated) have been observed by both visible and infrared transient absorption spectroscopy, allowing monitoring of the metal complex and DNA nucleobase intermediates respectively. Measurements carried out in D₂O show evidence for coupling of the photoinduced electron-transfer process to proton transfer.

Hopeahainol A containing an unprecedented carbon skeleton was characterized as an acetylcholinesterase inhibitor—with its activity comparable to that of huperzine A—from the stem bark of Hopea hainanensis (see figure) which contains two more new polyphenols. Its structure was elucidated by a combination of spectroscopic and single-crystal X-ray analyses along with computational calculations.

Charge for pore entry: Amphiphilic heptapeptides that contained residues of glutamic acid or its ester were found to self-assemble to form anion-conducting pores in phospholipid bilayers (see figure). Studies showed that chloride transport was dependent on the position of glutamate in the peptide chain and on the presence or absence of a free carboxylate group.