Chemistry - A European Journal

Lone-pair stereochemical activity plays a key structural role in lead(II)-based coordination polymers. In their Full Paper on page 3609 ff., S. Kroeker et al. show that ²⁰⁷Pb solid-state NMR spectroscopy offers a unique spectroscopic probe linking structural and electronic characteristics with optical properties, providing a predictive tool for materials design.

A series of dendron–dye… … conjugates that fluoresce in the near-IR region were synthesized. The conjugates display high chemical and photo stability and high quantum yields, which are optimal properties for in vivo imaging. For more details see the Full Paper by M. Weck et al. on page 3619 ff.

Is β better? Metal–ligand cooperative bifunctional catalysis is attractive in terms of highly effective molecular and energy transformations. This Minireview provides an overview of the chemistry of bifunctional pyrazole and N-heterocyclic carbene (NHC) complexes bearing a Brønsted acidic NH group at the β-position to the metal. Their potential as bifunctional catalysts is focused upon.

Let's split the difference: Nonchiral porphine macrocycles have been used as chemical shift agents for the determination of the enantiomeric excesses of chiral carboxylic acids. This method is based on the observation of the relative splitting induced in the ¹H NMR resonances of the porphine protons. A mechanism for the recognition based on the fast exchange of the guest molecules has been proposed (see scheme).

His-tones are not ruth-less: A ruthenium anticancer agent, RAPTA-C, was found to associate with chromatin in cancer cells and to form stable, well-defined adducts in the nucleosome core at specific histone protein sites (see picture). This illuminates the macromolecular binding properties of this antimetastasis agent and indicates potential for developing metallodrugs for site-selective targeting of chromatin.

Removable and versatile: The 2-pyridylsulfinyl group has proved to be an efficient directing group in the Pd^II-catalyzed aryl ortho CH olefination. This catalyst system enables the sequential double olefination to give asymmetrically di-ortho-functionalized arenes. The sulfinyl directing group can be easily cleaved, providing access to 1,3-disubstituted arenes, or transformed into a thiol group.

Highly enantioselective Mannich and α-amination reactions have been successfully developed using α-fluorinated aromatic ketones as fluorocarbon nucleophiles in the presence of a bicyclic chiral guanidine (see scheme; Ms=methanesulfonyl). This method is a simple and efficient approach to the construction of fluorinated quaternary stereogenic centers.

Superbase: According to density functional theory predictions, the title compound (see scheme) should be an O-symmetric aliphatic amine and a highly potent superbase.

The secret is in the net: A 3D mixed ligated cobalt phosphonate [Co₃(pna)₂(L)(H₂O)₂] (1) (pnaH₃=6-phosphonic nicotinic acid, L=1,4-bis(imidazol-1-ylmethyl)benzene) contains isolated ferromagnetic chains with interchain magnetic interactions. It experiences long-range magnetic ordering at approximately 3.4 K, below which magnetization relaxation and large coercivity are observed.

Heterocycles in one click: A novel organocatalytic enamide–azide cycloaddition reaction has been developed. This synthetic procedure represents a new method for the efficient construction of 1,4,5-trisubstituted-1,2,3-triazoles under mild reaction conditions. Most significantly, the investigated process is highly regiospecific (see scheme).

Inexpensive and simple: The direct arylation of unactivated arenes with aryl halides has been carried out with [Co(acac)₃] as the catalyst and LiHMDS as the base. The corresponding biaryl compounds have been prepared in good to excellent yields and at a relatively low reaction temperature (see scheme; acac=acetylacetonate, LiHMDS=lithium bis(trimethylsilyl)amide). An intramolecular direct arylation has also been achieved under the same conditions.

From noble to normal: Many transition-metal complexes have shown a remarkable ability to catalyze the cross-coupling of aryl halides with arenes (see scheme). The formation of biaryls has thus been achieved using inexpensive, readily available, and sometimes nontoxic transition-metal complexes. Not only “noble” transition metals, but also many of the “normal” transition metals are able to promote the direct transformation of CH bonds.

Chiral assemblies: Chiral hexameric perylene bisimide supramolecular complexes are constructed by using complementary 3:1 hydrogen-bonding interactions. The complexes hierarchically organize into semiconductive, gel-forming fibrous assemblies, exhibiting the “majority-rules” chiral amplification effect.

Two is the lone-liest number: A series of Pb²⁺ coordination polymers with varying degrees of birefringence is presented (see scheme). Crystallography, ²⁰⁷Pb NMR spectroscopy and DFT calculations assist in elucidating the interdependencies linking Pb stereochemical lone-pair activity, ligand basicity, ²⁰⁷Pb NMR chemical shift anisotropy and birefringence.

Fluorescent “trees”: Dendron–dye conjugates (see scheme for an example) that show fluorescence in the near-IR (NIR) region were obtained in high yields and displayed high chemical stability and photostability. All compounds show large Stokes shifts and strong fluorescence in the NIR region with high quantum yields; these are optimal properties for in vivo optical imaging.

A full account of our development of a short and efficient synthesis of (−)-oseltamivir is reported. Several synthetic route revisions are included. The final synthetic route features a novel palladium-catalyzed asymmetric allylic alkylation reaction (Pd-AAA, see scheme) as well as a rhodium-catalyzed chemo-, regio-, and stereoselective aziridination reaction. The eight-step synthetic sequence proceeds with an overall yield of 30 %. Phth=phthaloyl.

Rare earthly attraction: Metal–organic frameworks (see figure) were obtained by treating Ln^III ions (Ln=Sm, Eu, Gd, Tb, Dy) with open- or closed-shell polychlorotriphenylmethyl (PTM) ligands. Compounds based on the diamagnetic ligand showed metal-centered luminescence. The magnetic properties were used to investigate the {Ln–radical} interactions in radical-based complexes; these are found to be ferromagnetic for Ln=Gd, Tb and Dy.

SiW₁₂-AA microtubes (AA=ascorbic acid) were formed in two steps: the transformation of [α-SiW₁₁O₃₉]⁸⁻ to [α-SiW₁₂O₄₀]⁴⁻ anions at a low pH and growth of tubular crystals (see scheme). During the growing process of the hollow structure, AA molecules were doped. By using this method, various components could be doped into the microtubes, hence opening a way to functionalize polyoxometalates (POMs) with hollow structures.

Trapped en route: The irradiation of a new trans-2-hydroxychalcone derivative allows the formation of a lactone-stabilized chromene in noncompetitive solvents, thus opening a new route to exploit photochromism in flavylium systems (see scheme).

Tautomerization and symmetry: The rate constants of the intramolecular double hydrogen transfer in two similar porphycenes with symmetric and asymmetric character of a double potential minimum for hydrogen motion have been determined (see figure). The perturbation preserves a quasi-symmetric minimum in the ground state, whereas in the excited state the perturbed potential becomes strongly asymmetric, and the downhill hydrogen transfer occurs with a rate higher than that observed for a symmetrical compound.

SO versatile: The development of a catalytic asymmetric synthesis of β-sultones enables rapid access to a number of highly enantioenriched sulfonyl and sulfinyl compound classes (see scheme), which makes use of the inherent ring strain of the four-membered heterocycles. This work represents the first application of sulfene intermediates in asymmetric catalysis.

Moving four-ward: Four different types of square-planar Pt₄ clusters were prepared by using selective substitution reactions of in-plane acetate ligands of [Pt₄(μ-OCOCH₃)₈] with appropriate capping ligands. Cyclic dimers and a linear dimer were prepared by reactions of the Pt₄ complexes with dicarboxylic acids (see figure for an example).

Daylight plasmonic photocatalysis comes true! A daylight-driven AgCl/Ag plasmonic photocatalyst has been directly synthesized by a facile and rapid microwave-assisted nonaqueous route. The AgCl/Ag exhibits excellent daylight-driven photocatalytic activity for the degradation of various organic compounds (see picture), and is very promising for the degradation of organic pollutants around the clock under fluorescent lamp illumination.

Organometallic RAFT agents: Cr and Mo pentacarbonyl complexes of phosphinocarbodithioates have been synthesised and fully characterised (see graphic). They behave as excellent reversible addition–fragmentation chain transfer (RAFT) agents for the reversible deactivation radical polymerisation of styrene and n-butyl acrylate, and related block copolymerisation.

Peptide NGF(1-14), encompassing the sequence 1–14 of the amino-terminal domain of human nerve growth factor (NGF), is able to bind Cu²⁺ and Zn²⁺. The free amino group of the first amino acid (Ser1) is the anchoring site for Cu²⁺ and is involved in Zn²⁺ coordination at physiological pH (see figure). NGF(1-14) can mimic the proliferative activity of whole NGF protein. The activity of both NGF(1-14) and the whole NGF protein is enhanced in the presence of copper ions.

Molten-salt corrosion of PbSe solid nanoparticle aggregates formed in situ during high-temperature ripening affords hollow nanostructure assemblies (HNSAs; see SEM images). The ripening temperature affects the degree of etching and causes phase transitions. The HNSAs exhibit excellent electrogenerated chemiluminescence (ECL; see plot) performance due to strong electron coupling between adjacent HNS units.

Step by step: A DFT investigation of the formation of the Fe^IVO hydroxylating intermediate in the catalytic cycle of the aromatic amino acid hydroxylases shows that the overall heterolytic cleavage of the OO bond is achieved in sequential radical processes. A transition state along the route to the hydroxylating intermediate is shown.

Multi-tasking: Fullerene (C₆₀) and 3,4,9,10-perylene tetracarboxylic diimide (PTDCI) were used as building blocks for an electron-acceptor dyad (C₆₀–PTCDI) and triad (C₆₀–PTCDI–C₆₀). The reversible electrochemical switching of the fullerene–perylene conjugate molecules (see graphic) to polyanionic states, possessing up to three spatially separated unpaired electrons and some interesting optical properties were investigated.

Breaking through: The enantioselective Henry reaction between alkyl- and arylglyoxal hydrates and nitromethane catalyzed by Cu^II–iminopyridine complexes takes place regioselectively on the ketone carbonyl group to give chiral tertiary nitroaldols with high functional group density and enantiomeric excess (ee) values of up to 96 % (see scheme).

Cluster around: The site-specific growth of fluorescent silver nanoclusters by using mismatched double-stranded DNA as a template is described (see figure). The Ag clusters could be utilized as fluorescent probes to identify single-nucleotide polymorphisms. This approach offers the possibility of constructing novel DNA-based nanomaterials and nanomechanical devices.

Stability rules! By using accurate ab initio calculations the stabilities of glycyl, tyrosyl, and cysteinyl radicals (A–C, respectively) have been compared with other protein-derived radicals. All three radicals are found to be of comparable and high stability. In contrast, more highly substituted C_α peptide radicals are found to be less stable than the glycyl radical.