Angewandte Chemie International Edition

Hierarchically structured ZnO photoanodes for dye-sensitized solar cells can be fabricated by spray pyrolysis, as shown by A. Vomiero and co-workers in their Communication on page 12 321 ff. These photoanodes can achieve a top photoconversion efficiency of 7.5 %, as for ZnO-based cells. The technique is simple, cheap, and it can be scaled up to cover large areas.

No need to look into the crystal ball mass spectrometric studies and computational methods reveal for the first time that a bimetallic oxide cluster couple, AlVO₃⁺/AlVO₄⁺, provides an ideal model for the room-temperature catalytic oxidation of CO by N₂O. In their Communication on page 12 351 ff. H. Schwarz, M. Schlangen, and co-workers show that the overall catalytic process is promoted by the radical oxygen center of the AlO_terminal^. unit and not by the VO_terminal moiety.

The marriage of coordination chemistry and catalysis enables metal ions to work in partnership in the active-template synthesis of the smallest molecular trefoil knot reported to date. In their Communication on page 12 280 ff., D. A. Leigh et al. describe how one copper(I) ion entangles an acyclic building block to create a loop in the ligand whilst a second copper(I) ion gathers the ligand′s reactive end groups, threads the loop, and catalyzes the covalent capture of the 76-atom knot by an alkyne–azide “click” reaction.

“The biggest problem that scientists face is the pursuit of fame and fortune. If I won the lottery, I would stop applying for grants and concentrate on oxidative coupling research just for fun! …” This and more about Aiwen Lei can be found on page 12136.

Oxford University Press, 2010. 712 pp., hardcover, $ 90.00.—ISBN 978-0198525264

No two ways about it: The title reaction is immensely important in synthesis and biology. Whereas biological systems oxygenate aldehydes to generate formate and alkanes or alkenes, synthetic deformylation reactions primarily rely on rapid oxidative addition into the C(O)H bond and subsequent rate-determining extrusion of CO.

DNA methyltransferases catalyze the transfer of methyl groups to cytosines within DNA. Afterwards, 5-methylcytosine is oxidized to 5-hydroxymethylcytosine. Two further cytosine derivatives, 5-formylcytosine and 5-carboxycytosine, have been discovered recently. The existence of the seventh and eighth nucleobase provides new hints for deciphering the process of active DNA demethylation (see scheme).

Simple and practical: Direct intermolecular α alkylation reactions by S_N1-type transformations have been developed and offer flexible and robust routes to major compound classes, for which the direct preparations were unavailable before.

It's back: This Minireview summarizes the development of urea chemistry during the last few years by taking examples to illustrate each of the themes associated with this renaissance—ureas as lithiation directors, the design of urea-based catalysts and supramolecular structures, the increased reactivity that is characteristic of more hindered ureas, and the electrophilicity disguised within electron-rich aromatic ureas (see picture).

Light of my life: The merger of natural transmembrane proteins with synthetic photoswitches creates hybrid receptors that can be integrated into complex systems and regulated with the precision that only light provides. This strategy allows for the optical control of single cells, neural systems, and can even be used to control animal behavior.

Away from the surface: Novel nanoparticles (NPs) consisting of 16 nm Au cores surrounded by Pd shells of various thicknesses catalyze Suzuki–Miyaura cross-coupling reactions in water at room temperature. NPs having shells of two to five Pd monolayers thick exhibit the highest catalytic activity. Catalysis was attributed to the leaching of Pd species from the NPs through the synergistic action of the carbonate base and the arylboronic acid.

Swapped selectivities: The use of tailor-made catalysts results in anomalous endo/exo selectivities and high enantioselectivities in the Diels–Alder reactions of cyclopentadiene with different acroleins (see scheme). These supramolecular catalysts are prepared in situ from chiral diols, arylboronic acid, and tris(pentafluorophenyl)borane, and can discriminate the re/si face of the dienophile as well as the endo/exo approach of the diene.

Regioisomeric MOFs: A series of bifunctional metal–organic framework (MOF) regioisomers has been produced from amino-halo benzene dicarboxylate (NH₂X-BDC) ligands. Zr^IV- and Zn^II-based MOFs were synthesized and for the flexbile Zn^II-based MOFs, gas sorption properties were dependent on the ligand substitution pattern.

AnEZswitch: The cationic species of the heteropoly compounds has a critical impact on the Z/E selectivity of the Meyer–Schuster rearrangement of propargyl alcohols (see scheme). The isolation of the thermodynamically unfavorable Z-α,β-unsaturated carbonyl compounds is notable. The high Z selectivities were obtained at a reaction temperature as high as 50 °C.

Form-fitting: The study of a minimal mimic of a protein domain that binds to type II polyproline helices through an aromatic cleft is reported. This binding motif mimics that of protein domains, including those important in disease states such as HIV infection and cancer. This study provides insight into the structure–function relationship in binding as well as quantitative data on the magnitude of prolyl–π interactions relevant to inhibitor design.

Unusual bonding: A ligand system that promotes formation of a rare μ-η¹:η¹ acetonitrile-bridged dicopper(I) complex (see picture) has been developed. The acetonitrile ligand is involved in a three-center two-electron bond supported by a cuprophilic interaction. The labile acetonitrile ligand can be substituted with xylyl isocyanide or CO.

Small changes go a long way: Modification of the terminal ligand to incorporate 4,7-diphenyl-1,10-phenanthroline has generated superior Ru,Rh,Ru photocatalysts (see scheme; ochre Ru, red Rh, blue N, yellow Cl or Br) displaying significantly enhanced photocatalytic H₂ production from H₂O with long-term functioning: H₂O is reduced to H₂ with over 1300 turnovers per Rh site and a maximum efficiency of 7.3 %.

To dye for: Three related families of fluorescent dyes, rigidified by boron difluoride and based on bidentate anilido-pyridyl donor ligands, are reported (see picture). The dyes show quantum yields up to 0.75 and improved Stokes shifts of >100 nm relative to the widely employed BODIPY family of dyes. Furthermore, the new dyes are exceptionally photostable and membrane-specific.

Size matters: A highly ordered mesoporous carbon material (OMC) was synthesized by a soft-template method, and was applied as an adsorbent for the highly efficient extraction of endogenous peptides from human serum (see scheme). A total of 3402 different peptides were identified from only 20 μL of human serum.

Cyclopropenone makes the switch: 2,3-Bis-(p-methoxyphenyl)cyclopropenone is a highly efficient catalyst for the chlorodehydration of 20 diverse alcohol substrates (see scheme; X=Cl). With oxalyl chloride as catalytic activator, this nucleophilic substitution proceeded through cyclopropenium-activated intermediates and resulted in complete stereochemical inversion in substrates with chiral centers.

Channeling the frustration: Frustrated Lewis pairs (FLPs) consisting of Ar^F₂BH 1 with NEt₃ or DABCO can activate H₂ under mild conditions. Theoretical calculations suggest two distinct reaction pathways for these two FLPs. For the “more frustrated” Ar^F₂BH/NEt₃, H₂ is activated in a stepwise manner; for the “less frustrated” Ar^F₂BH/DABCO, H₂ is activated in a concerted fashion (see scheme).

Step saver: Carbonyl groups with lower reactivities can be transformed in the presence of more reactive ones by treatment with PPh₃ (or PEt₃) and TMSOTf prior to the reaction (see scheme; TMS=trimethylsilyl, Tf=trifluoromethanesulfonyl). This methodology can be applied to reduction and alkylation reactions, and enabled the short asymmetric total synthesis of (+)-centrolobine with the highest overall yield reported to date.

Simplified access: Substituted benzolactones can be obtained in one step by a Pd-catalyzed ligand-accelerated C(sp³)H bond-activation/C(sp³)O bond-formation protocol. This step-economical approach enables the preparation of benzolactones with a wide variety of functional groups and different substitution patterns. The method is characterized by its simplicity and the avoidance of protecting groups.

Your choice: The choice of the Ru-pincer-complex catalyst determines if peptides or pyrazines are formed from β-amino alcohols. Use of PNN complex 1 leads to linear poly(alanine) or to cyclic dipeptides, depending on the R group (see scheme). With the PNP complex 2, pyrazines are formed. These reactions are homogeneously catalyzed under neutral conditions and are environmentally benign.

It's hip to be square: Gold square-like plates exhibit alternating hexagonal close-packed (hcp, see picture, yellow) and face-centered cubic (fcc, red) structures in the center and defect-free fcc structures at one pair of the opposite thick edges. They can be synthesized from Au square sheets in a secondary growth process. For the first time, the hcp-to-fcc phase transformation associated with shape variation in Au nanostructures is demonstrated.

Three high-yielding steps lead to the formation of chiral 1,3-diaminopropanols from aliphatic and aromatic α-keto amides. In this approach, a nitroaldol reaction, which is catalyzed by Cu(SO₂CF₃)₂ and the bisoxazolidine ligand L1, is followed by two mild reduction reactions (see scheme). Laborious protection and deprotection steps can be avoided by using this method.

Out of the norm: The first deviation from the ortho effect in palladium/norbornene catalysis, as evidenced by the resulting products, is reported (see scheme). DFT calculations indicate that this deviation is likely to originate from a distortion, caused by specific chelation, in the reductive-elimination pathway from the Pd^IV intermediate initially formed. Addition of water restores the normal selectivity, but also it leads to dearomatization.

Expecting the unexpected: The title reaction leads to satisfactory yields of dihydrodibenzoazepines 1 a from norbornene. The dibenzoazepines 2 can also be accessed from compounds of type 1 b when norbornadiene is used as a reactant. Theoretical studies show that the reaction represents a chelation-driven deviation from the usual selectivity observed in the presence of ortho-substituents on the aryl iodide.

Two birds with one stone: In the presence of Zn(OH)₂ and a chiral bipyridine ligand, racemic α-substituted allylboronates 2 reacted with aldehydes 1 (see scheme) exclusively in an α-addition fashion to afford various homoallylic alcohols 3 bearing two neighboring stereogenic centers in high yields with high diastereo- and enantioselectivities.

Electrifying! A device based on carbon nanotubes wrapped with poly(3-hexylthiophene) (and dispersed in poly(dimethylsiloxane)) sheets can effectively convert laser light into thermal energy and subsequently to electricity. The converter is flexible and extremely compact (see picture), and can be manipulated by using a laser that functions in the wavelength range that can be transmitted through living tissue.

Hard and soft: Binding of inorganic Pt@Fe₃O₄ Janus particles to WS₂ nanotubes through their Pt or Fe₃O₄ domains is governed by the difference in Pearson hardness: the soft Pt block has a higher sulfur affinity than the harder magnetite face; thus the binding proceeds preferentially through the Pt face. This binding preference can be reversed by masking the Pt face with an organic protecting group.

A successful team: A molecular device based on multiwalled carbon nanotubes functionalized by a mononuclear ruthenium catalyst has been shown to split water electrochemically (see picture; ITO=indium tin oxide). The readily prepared electrode showed excellent electrocatalytic activity for the oxidation of water, a high current density, and a low overpotential, and constitutes one step forward in the design of artificial photosynthetic systems.

Tying the knot: The marriage of catalysis and coordination chemistry enables two Cu^I ions (red; see picture) to work in partnership for the synthesis of a molecular trefoil knot. One ion entangles an acyclic building block to create a loop in the ligand, and the other gathers the ligand's reactive end-groups, threads the loop, and catalyzes the covalent capture of the knotted architecture by an alkyne–azide “click” reaction.

A multisegment amphiphile, made of a gelator and a surfactant, self-assembles into architectures with properties inherited from both segments. By addition of a surfactant, the surfactant segment of the amphiphile is selectively switched off, leading to the formation of fibrils. The addition of urea or hexafluoroisopropyl alcohol (HFIP) switches off the gelator segment, giving micelles.

Crosslinking vesicles with magnetic nanoparticles produced MNPVs, self-assembled “nanopills” that can be “unlocked” by an alternating magnetic field (AMF), releasing chemical messengers stored within the vesicles. When MNPVs are co-immobilized with cells in a hydrogel matrix, exposure to an AMF magnetic signal releases the chemical messengers, which then induce a cellular response.

Crystal clear: Uniform Cu₂O nanooctahedra (o-Cu₂O) and nanocubes (c-Cu₂O) undergo surface restructuring during CO oxidation for the in-situ formation of catalytically active CuO thin films to give CuO/o-Cu₂O and CuO/c-Cu₂O, respectively (see picture). The structure and catalytic performance of CuO thin films are controlled by the crystal plane exposed on the underlying Cu₂O nanocrystals.

Ultrasmall but multifunctional: Rigid imaging particles that are smaller than 5 nm in size can be obtained in a top-down process starting from a core–shell structure (core=gadolinium oxide; shell=polysiloxane). They represent the first multifunctional silica-based particles that are sufficiently small to escape hepatic clearance and enable animal imaging by four complementary techniques.

Chosen handle: Mechanistic studies of the IspH-catalyzed reductive dehydroxylation of 4-hydroxy-3-methyl-2-(E)-1-diphosphate (HMBPP) to isopentenyl diphosphate and dimethylallyl diphosphate suggest that both the 4-OH group and the double bond of HMBPP may contribute to the formation of substrate–IspH complex. Labeling studies now show that the 4-hydroxy group of the substrate plays the dominant role in positioning the substrate in the enzyme active site.

Enhanced visualization of breast cancer in X-ray computed tomography was achieved by using Bi₂S₃ nanoparticles of 10 nm diameter modified to display a tumor targeting peptide (LyP-1, CGNKRTRGC). Accumulation within the tumor was increased by 260 % over non-labeled nanoparticles.

Gold nanoparticles coated with homogeneous (MUS) or “striped” (MUS-OT) ligand shells can be conjugated with double or single stranded DNA, and particles with either ligand configuration effectively carry DNA into melanoma tumor cells. When endocytosis is inhibited, however, MUS-OT particles continue to mediate DNA delivery, while the delivery ability of MUS particles is abolished.

Roll 'em up, move 'em out: The growth of SnS₂ and SnS₂/SnS nanotubes and nanoscrolls with ordered superstructures is promoted by the relaxation of stress between adjacent SnS₂ and SnS layers. Partial decomposition of the SnS₂ precursor to more sulfur-deficient SnS was manifested in the exfoliation of layers and scrolling. The presence of the two main structures (see picture) was confirmed by HRTEM and Raman spectroscopy.

Spray pyrolysis is effective in the formation of a nanoengineered photoanode. An unprecedented photoconversion efficiency of 7.5 % for ZnO-based dye-sensitized cells was achieved on a photoelectrode consisting of polydispersed ZnO aggregates of nanocrystallites over a compact ZnO buffer layer at a firing temperature of 450 °C. FTO= fluorine-doped tin oxide.

A hard capsule gets soft: The exchange of 60 oxide by 60 sulfide ligands (see picture) in a well-known porous metal-oxide capsule skeleton conataining 132 metal atoms changes the interior properties as well as pore sizes, reactivities, flexibilities and affinities to guest molecules.

Dopant-induced phenomena: Doping with sodium ions can stimulate the formation of monodisperse ultrathin La₂O₂S nanoplates with tunable self-assembled superstructures (see picture) and robust fluorescence in surfactant solutions by creating oxygen vacancies in the host lattice during sulfurization reactions.

Coppertunity knocks: An inexpensive, practical, and environmentally benign procedure for the enantioselective addition of glycine derivatives to α,β-unsaturated ketones has been developed (see scheme). By modifying the workup, the conjugate addition product or a cyclic imine can be accessed. The solution structure of the catalyst–substrate complex is shown to be key to the overall reaction selectivity.

New ligands: The first examples of a neutral heteroborane and a neutral metallaheteroborane acting as simple σ-bound ligands to transition metals are described. In [HCo(1,2-closo-P₂B₁₀H₁₀)₂(PEt₃)₂] (see structure, left) the P₂B₁₀H₁₀ ligand coordinates to Co through one P atom, and in μ-[1,2-{HRu(p-cymene)}₂-7′,8′-nido-P₂B₉H₉]-3-(p-cymene)-3,1,2-closo-RuP₂B₉H₉ (right) both closo-RuP₂B₉ and nido-P₂B₉ cages act as bridging κP:κP′ ligands.

Green oxidation: A new class of Group 6 metal complexes catalyzes the direct oxidation of isocyanides through nondegenerate oxygen atom transfer (OAT) utilizing N₂O as a chemical oxidant. In addition they serve as photocatalysts for the reversible degenerate OAT between CO and CO₂ (see scheme).

Happily coupled: Photosystem II and photosystem I can be coupled in a sol–gel system so that electron flow can be directly mediated from photooxidized water at the donor side of photosystem II to the highly reducing acceptor side of photosystem I. The electron transfer pathway is set up by addition of the amphipathic quinone analogue 2,6dichlorophenolindophenol (DCPIP) to the sol–gel mixture to provide a pool of redox carriers (see picture).

Exhaustive studies: The exact reaction pathway of catalytic conversion of automobile exhaust gases, such as N₂O and CO, into N₂ and CO₂ is still not completely understood. Studying this reaction at room temperature using the bimetallic oxide cluster couple AlVO₃⁺/AlVO₄⁺ in the gas phase shows that the active M-O_t^. site is located at the Al-bound and not the V-bound oxygen atom (see scheme, Al pink).

A touch of acid: Catalytic amounts of HNO₃ can trigger the aerobic oxidation of alcohols in the presence of the solid acid amberlyst-15. The desired oxidation cycle, mediated by (H)NO_x species, is in kinetic competition with the detrimental formation of N₂O by HNO dimerization (see scheme). In situ water removal in a gas recirculation reactor increases the reaction rate and the end-conversion by minimizing N₂O formation and increasing the (H)NO_x turnover.

A molecular metal disulfate, Re₂O₄Cl₂(S₂O₇)₂ forms in the reaction of ReCl₅ and oleum (65 % SO₃) under harsh conditions. The first of its kind, this unique Re^VII compound contains two ReO₂Cl fragments linked by two disulfate groups, leading to C_i-symmetric molecules (see picture; Re red, O blue, S yellow, Cl green).