Chemistry - A European Journal

Single-Site Catalytic green production of Niacin is reported by R. Raja, J. M. Thomas et al. on page 2340 ff. The compound, which is used for the preparation of Vitamin B₃, is obtained in a single-step, solvent-free, and environmentally benign manner with a solid source of active oxygen.

Tris(trimethylsilyl)silane: The flexibility and applicability of (Me₃Si)₃SiH in several synthetic transformations are described. The reactivity of (Me₃Si)₃SiH penetrates areas as diverse as organic synthesis and materials science.

A modular assembly of the individual thiazole fragments to the central pyridine core was achieved by regioselective cross-coupling reactions giving access to the title compound (see graphic) in an overall yield of 4.8 % over 20 steps. The successful implementation of orthogonal metallation and protecting group strategies further contributed to the brevity of the total synthesis.

It's green and selective! Single-site heterogeneous catalysts (shown here) can be judiciously combined with a solid source of active oxygen for the single-step, solvent-free, and environmentally benign production of Niacin (used in the preparation of Vitamin B₃) and other fine-chemical, pharmaceutical, and agrochemical intermediates.

Sea urchin architectures: The design of polyoxometalate nanoscale hybrid assemblies comprising a core–shell hydrophilic–hydrophobic structure has been achieved by covalently tethering alkyl chains (C₆, C₁₆ and C₁₈) to a Mn-Anderson cluster core producing a surface-grafted cluster architecture. The resulting compounds give highly organized structures on silicon substrates as 1D rods with tetrabutyl ammonium (TBA⁺; see graphic) and 3D-spherical or sea urchin architectures with dimethyl dioctadecyl ammonium (DMDOA⁺).

All self-organized: A thiol-functionalized, heterometallic carbonyl cluster [RuCo₃(CO)₁₁(H)(Ph₂PCH₂CH₂SH)] (see picture) has been self-assembled on a Au(111) surface. Thermal annealing of this cluster in ultra-high vacuum led to the formation of a bimetallic alloy. Preliminary experiments indicate that the double cluster, with a disulfide linkage between two {RuCo₃} tetrahedra, behaves similarly.

How do you want your eggs? Magnetic resonance imaging (MRI) was used to monitor the distribution of paramagnetic metal-ion complexes inside catalyst extrudates. By addition of citric acid to the impregnation solution, the distribution of Co²⁺ complexes inside Al₂O₃ bodies could be varied from eggshell through egg white and egg yolk to uniform. In all cases, the distribution was reliably determined by MRI in a noninvasive manner (see picture).

Prebiotic nucleotide assembly—back to basics? Arabinose-3-phosphate can be converted into an activated nucleotide under potentially prebiotic conditions (see scheme), but can this ostensibly simple sugar phosphate—or its cyanamide derivative—self-assemble from simple building blocks?

Empty honeycombs: The topotactic dehydration reaction of two coordination polymers was studied by powder X-ray diffraction using synchrotron radiation. The process is smooth and continuous for the cobalt compound with the coordinatively bound water molecule leaving last as evidenced by the progression of site-occupancy factors (see figure). In contrast, the isostructural zinc compound passes through several distinct phases.

Entrapped structures: If single-walled carbon nanotubes (SWNTs) are entrapped into the helical superstructure of either cationic or anionic semi-artificial β-1,3-glucans, then these oppositely-charged SWNT composites can be easily organized into their hierarchical structures that feature the ordered SWNT structure (see graphic).

Very receptive: High binding affinity and selectivity of new carbohydrate receptors (depicted in figure) was achieved through the participation of different types of binding units, which included recognition units that are used in nature as well as analogues of the natural units, in the recognition process. The design of these receptors was inspired by the analysis of the binding motifs found in the crystal structures of protein–carbohydrate receptors.

Two new catalytic systems were developed to carry out stereoselective addition of dialkyldichalcogenides (Alk₂E₂; E=S, Se) to terminal alkynes (see scheme). A comparative study has revealed that the Ni catalyst is superior with respect to high catalytic activity and wide scope. The advantages and disadvantages of both catalytic systems (Ni and Pd) were analyzed in details in the present study.

In the groove: Selective-frequency saturation-transfer-difference spectra allow the description of complexes established between minor-groove binders (such as 1 and 2; β-L-Fuc: β-L-fucose; Py: N-methylpyrrole; γ: γ-aminobutyric linker; Ind: indole) and long tracts of calf thymus DNA.

A practical protocol for the amination of aryl chlorides and bromides catalyzed by Pd-PEPPSI precatalysts affords a range of sterically hindered and functionalized, drug-like aryl amines in good to excellent yield under strongly (tBuOK) or weakly basic (Cs₂CO₃) conditions.

A series of thermal pericyclic reactions of β-allenylfuranones have been studied. It was observed that β-allenylfuranones would undergo 1,5-hydrogen shifts to afford new types of trienes upon heating. Due to their high reactivity, these trienes would undergo subsequent pericyclic reactions based on the nature of the substituent group R (see scheme).

The modular approach: The introduction of an amide function at C-16 and a polyamine moiety on the mycosamine of amphotericin B (see graphic) lead to a significant improvement in antifungal activity and reduced toxicity.

Sliding makes it easy: The synthesis, structure, and specific linkage isomerization of bistable C- and N-bound isomers of transition-metal cyanocarbanions are described. Experimental and theoretical studies revealed that both the N-to-C and C-to-N isomerizations proceed unimolecularly through the sliding of the metal atom over the CCN surface (see graphic).

Cyclopentene derivatives have been mono- and difunctionalised in a one-pot reaction using Br/Mg exchange. A β-bromocyclopentenylmagnesium intermediate was prepared from 1,2-dibromocyclopentene and iPrMgCl⋅ LiCl. Treatment of this Grignard reagent with a range of electrophiles gave the corresponding substituted cyclopentenes in good yields. Substitution of the second bromo substituent permitted difunctionalisation.

Advancing nanotechnology: A method of direct thermal decomposition of metal nitrates was developed to synthesize various metal oxide nanocrystals, such as Mn₃O₄, NiO, ZnO, CeO₂, CoO, and Co₃O₄, with controllable shape and size. The nanocrystals were used as building blocks to construct meso-architectures (figure right). The as-obtained mesoporous metal oxides show potential applications in catalysis and lithium-ion batteries.

Single-molecule magnets: Pseudohalide substitution in the ferrous enneanuclear complex [Fe₉(OH)₂(O₂CMe)₈{(2-py)₂CO₂}₄] does not disrupt its structure, but leads to the analogous N₃⁻ and NCO⁻ complexes (see graphic). These exhibit stronger ferromagnetic interactions and higher ground-state spins. They are also found to behave as single-molecule magnets at low temperatures.

Multiple-ring synthesis: Hexahydronaphthacenes and octahydroanthracenes can be formed by a palladium-catalyzed domino Tsuji–Trost–Heck–Mizoroki reaction with starting materials that contain an allyl acetate and a halogen aryl moiety (see scheme; dppe: 1,2-bis(diphenylphosphino)ethane). The octahydroanthracene and hexahydronaphthacene motifs are found in many natural products, such as the tetracycline antibiotics.

More rational design of sequence-selective peptide receptors: Coordination chemistry and ammonium ion recognition by crown ethers join forces in a luminescent peptide receptor with selectivity for glycine–histidine sequences (see graphic). Nearly micromolar affinities for GGH and GHG are observed.

Highly accurate: A methodology for computing lattice energies of neutral organic crystals within chemical accuracy is established and applied to crystalline benzene (see scheme). Three-body interactions are negligible for this system, but dimers beyond the first coordination sphere contribute about 10 % of the lattice energy.

Covalent grafting of the anthraquinone redox system onto glassy carbon (GC) electrodes via different linkers and spacers (see picture) has been achieved by using electrochemical and solid-phase synthesis methodologies. The surface coverage, stability and electron transfer of the tethered anthraquinone redox centre through the different spacers have been investigated by cyclic voltammetry, and the effects of pH and scanning rate studied.

Thetransandciscomplexes [OsCl₂P₂(Pyme)] (Pyme=1-(pyridin-2-yl)methanamine) efficiently catalyze the hydrogenation (turnover frequency (TOF) up to 1.5×10⁴ h⁻¹) and transfer hydrogenation (TH) of several ketones in basic alcohols (TOF up to 5.7×10⁵ h⁻¹; see scheme). High enantioselective TH (up to 96 %) has been observed by using [OsCl₂(PPh₃)₃] with chiral diphosphane and Pyme ligands.

Radical ping-pong: The complexes [Ni(N₂S₂)]⁺ switch between formal Ni^II–thiyl radical or Ni^III–thiolate states that are dependent on the nature of the axial ligands; the Ni^II–thiyl radical centers undergo S–S coupling to form Ni-S-S-Ni bonded dimers, which are, for the first time, characterized crystallographically (see graphic).

Unstable and spontaneous! One-step conversion of aromatic azine N-oxides into α-heteroaryl perfluoropropionyl fluorides. These fluorides can be used for the acylation of a wide range of nucleophiles (see scheme), whereas treatment of the fluorides in situ with water results in hydrolysis and instantaneous decarboxylation.

Reverse transitions: Mono- and ditopic, redox-active p-quinone-based bis(pyrazol-1-yl)methane ligands (see figure) have been prepared. These ligands can be oxidised on a preparative scale and complexes with palladium can be prepared that are active in CC coupling reactions.

A construction kit synthesis: Oligophenothiazines, such as depicted, can be easily synthesized by Suzuki coupling. They are highly fluorescent with high fluorescence quantum yields and large Stokes shifts, and are highly electroactive with low oxidation potentials.

A variety of coordination modes for the azide groups including κ¹, μ-1,3 and linkages via H-bonded water molecules in addition to azide ions are displayed by a series of azide complexes of Ca, Sr and Ba with crown ethers. For example, [Ba([18]crown-6)(N₃)₂(MeOH)]⋅1/3 MeOH contains dinuclear cations and three μ-1,3-NNN bridges (see picture), the first of this type in main group chemistry.