Angewandte Chemie International Edition

The hydrogenolysis of renewable feedstocks has the potential to become a bridging technology between the petrochemical industry and future biorefinery concepts. In their Review on page 2564 ff., R. Palkovits et al. highlight developments in this field, with a focus on catalysts for the transformation of mono- and polysaccharides. Various concepts applied in the utilization of glycerol and sugars provide valuable information for the efficient transformation of biopolymers.

Supramolecular coordination polymers based on stacked square-planar Pt^II complexes, such as Magnus' Salts, show potential as functional materials. In their Communication on page 2606 ff. G. H. Clever, M. Shionoya, and co-workers describe a linear array of five alternately stacked Pt^II complexes in the form of a soluble host–guest complex. The X-ray structure of {[Pt(pyridine)₄]⋅[PtCl₄]₂@cage} shows the linear, pentanuclear array within the cages and their circular packing into a hollow tubular superstructure.

Nucleophilic substitution belongs to the fundamental organic reaction mechanisms since the pioneering work of C. K. Ingold in the 1920s. In their Communication on page 2610 ff., H.-P. Steinrück and co-workers monitor the alkylation of a tertiary amine attached to an imidazolium cation with a chloroalkylsulfonate anion by photoelectron spectroscopy, which can distinguish between convalently bound chlorine (Cl_cov) and chloride (Cl_ion).

Wheel-like assemblies are fascinating and exquisite. Anderson-type molecular wheels (structures on the periphery first proposed in 1937 and right structure) each feature six skew-edge-shared octahedra. In their Communication on page 2614 ff., C. M. Che and co-workers report selective binding of Cu⁺ or Ag⁺ by isolated [{M(S-4-R-C₆H₄)₂(CO)₂}₆] (right structure to bottom-right structure) and isolation of [{M(SPh)₂(CO)₂}₈] (bottom left), thus demonstrating feasible expansion of Anderson-type wheels to octanuclear congeners.

“A good work day begins with an early morning workout at the gym. My favorite song is “Supper's Ready” by Genesis. …” This and more about Michael M. Haley can be found on page 2540.

Royal Society of Chemistry, Cambridge, 2011. 574 pp., hardcover, £ 280.00.—ISBN 978-1849730266

John Wiley & Sons, Hoboken, 2011. 480 pp., hardcover, € 129.00.—ISBN 978-0471780144

Collar and tie men: The smallest trefoil knot reported to date has been prepared by an active metal template synthesis. Copper(I) ions are able to constrain the well-designed structure so that it can form the loops by complexing to the bipyridine moieties in the core of the thread and the two ends of the entangled lace on opposite faces of the loop, before acting as a catalyst to close the lace (see picture).

Not your cup of tea? “Coffee rings” of spherical colloidal particles are left behind after water droplets resting on surfaces have dried out. This controlled evaporation of colloidal solutions can be exploited to deposit material in regular patterns (see picture). It is now shown that if spherical colloids are replaced by slightly elongated ones, the coffee ring is not formed and is replaced by an even more uniform deposition.

Not chiral, but temporarily stereogenic: The introduction of a diaryl(oxy)methyl group into chiral auxiliaries, catalysts, and dopants can be rewarding: As a temporary stereogenic unit, it has a beneficial effect in a variety of asymmetric syntheses and has helped a series of well-known, efficient, and reliable “work horses” to succeed.

Hydrogenolysis of renewable feedstocks allows direct access to valuable platform chemicals already integrated in today's value chains. Transformations based on hydrogenolysis bear the potential to bridge available technologies and future biorefinery concepts. This Review highlights developments in this field, with special emphasis on the direct transformation of cellulose and sugars.

Attack or defend! A smart polymer surface has two reversibly switchable equilibrium states, a cationic N,N-dimethyl-2-morpholinone (CB-Ring) and a zwitterionic carboxy betaine (CB-OH). CB-Ring will kill bacteria upon contact under dry conditions, whereas CB-OH will release the previously attached and dead bacteria and further resist adhesion of bacteria under wet conditions.

Neatly wrapped up: Alternately stacked square-planar platinum(II) complexes inside a dinuclear coordination cage were prepared to give a discrete and soluble Pt₅-array of the Magnus' salt type. Characterization of the complex in solution was complemented by an X-ray crystal structure of {[Pt(pyridine)₄]⋅ [PtCl₄]₂@Cage}; this structure showed the linear, pentanuclear array within the cages and their circular packing into a hollow tubular superstructure.

There are strings attached: After linking the reacting groups to head groups of ionic liquids to drastically lower the vapour pressures of the reactants, ordinary liquid-phase organic reactions can be monitored by in situ X-ray photoelectron spectroscopy. This approach is demonstrated for the nucleophilic substitution of an alkyl amine and an alkyl chloride moiety, which are attached to the cation and anion of ionic liquids, respectively.

Inventing new wheels: Reaction of [M₃(CO)₁₂] (M=Ru, Os) with 4-RC₆H₄SH afforded [{M(S-4-RC₆H₄)₂(CO)₂}₈] (R=H; I) or [{M(S-4-RC₆H₄)₂(CO)₂}₆] (R=Me, iPr; II; see scheme), all of which have been structurally characterized. The octamers I are unique metal molecular wheels featuring skew-edge-shared octahedra with a central planar M₈ octagon. [{Ru(S-4-iPrC₆H₄)₂(CO)₂}₆] selectively binds a Cu⁺ or Ag⁺ ion to form [M′{Ru(S(4-iPr-C₆H₄))₂(CO)₂}₆]⁺ (III).

Well conducted: A two-dimensional porphyrin covalent organic framework is described. Owing to the eclipsed stacking alignment, the framework is conductive and allows high-rate carrier transport through the porphyrin columns (see picture). The central metal in the porphyrin rings changes the conducting nature of the material from hole to electron, and to ambipolar conduction. It also drives the high on–off ratio photoconductivity of the framework.

Expanding into application: Covalent organic framework (COF) films are ideally suited for vertical charge transport and serve as precursors of ordered heterojunctions. Their pores, however, were previously too small to accommodate continuous networks of complementary electron acceptors. Four phthalocyanine COFs with increased pore size well into the mesoporous regime are now described (see picture).

All connected: A protein-immobilized electrode comprising hierarchical assemblies of photoactive cytochrome b₅₆₂ reconstituted with zinc protoporphyrin IX exhibits remarkably enhanced photocurrent generation relative to an electrode bearing a single zinc-substituted hemoprotein layer. The protein oligomers, which bear a covalently linked protoporphyrin group, assemble by a supramolecular heme/heme pocket interaction.

Breaking through the stoichiometry barrier: As the diameter of silver particles is decreased below a critical size of 32 nm, the molar ratio of aqueous Hg^II to Ag⁰ drastically increases beyond the conventional Hg/Ag ratio of 0.5:1, leading to hyperstoichiometry with a maximum ratio of 1.125:1 (see figure). Therein, around 99 % of the initial silver is retained to rapidly form a solid amalgam with reduced mercury.

All in one: A tandem strategy has been developed wherein secondary aryl alcohols are directly coupled with aryl halides to provide stilbenoids through a dehydrative Heck sequence in the ionic liquid [hmim]Br, and with water as a by-product under microwave irradiation (see scheme). Classical methods do not permit this sequence to proceed in one pot, and some methods require multiple steps. hmim=1-n-hexyl-3-methylimidazolium.

An enhancing factor: The enhancement of the electric properties of a dye molecule (IR26) by indium–tin oxide nanoparticles (ITO NPs, see picture) has been shown by measuring the near-infrared two-photon-excited transient absorption spectra. The dye molecule was excited much more efficiently in the presence of an ITO NP layer.

In reduced circumstances: Tetrahydroxynaphthalene reductase shows a broad substrate range including alternate phenolic compounds and cyclic ketones. Structural modeling reveals major enzyme–substrate interactions; C-terminal truncation of the enzyme causes an altered substrate preference, in accordance with stabilization of the substrate by the C-terminal carboxylate (see picture). This effect allows the identification of a homologous enzyme.

Not quasi-crystalline: Approximate five-fold symmetry appears in bronze-type Cu–Sn rods that are separated by Na atoms in Na_2.8Cu₅Sn_5.6 (see picture). The rods are compared to the [Sn@Cu₁₂@Sn₂₀]¹²⁻ cluster in the recently characterized A₁₂Cu₁₂Sn₂₁ phases (A=Na–Cs), and a saltlike description in analogy to Zintl phases of p-block metals is introduced for these new polar intermetallic phases with a high d-block metal content.

In a spin: The dynamics of photoexcited ICN⁻(Ar)_0–5 are presented. Photodetachment produces quasi-thermal electron emission that leaves ICN with up to 2.85 eV of internal energy. Photodissociation at 2.5 eV leads to one-atom caging and highly solvated anion products. Calculations indicate efficient energy transfer into CN rotation upon excitation to the ²Π_1/2 excited state. CN rotation is vital to explain the unique dynamics observed.

All that glitters is gold: Highly phosphorescent gold(III) complexes (see picture) with extended π-conjugated cyclometalating ligands exhibit rich photophysical and photochemical properties. They act as efficient photocatalysts/photosensitizers for oxidative functionalizations of secondary and tertiary benzylic amines and homogeneous hydrogen production from a water/acetonitrile mixture.

A red light for cancer cells: An iron(III) complex (1, see picture) that contains an anthracenyl fluorophore moiety and a catecholate ligand is a potent, metal-based PDT agent that efficiently photocleaves DNA in near-infrared light, has significant nuclear uptake, and high photocytotoxicity in red light by an apoptotic pathway in HeLa and MCF-7 cancer cells.

Chemistry in motion: A combination of confocal microscopy (see picture) and reaction-diffusion modeling provided a powerful toolkit with which solution transport into metal–organic framework crystals was studied. Commonly used pure diffusion models are insufficient to describe this process and, instead, it is necessary to account for the interactions of the guest molecules and the MOF scaffold.

Problem solved: An air-stable 2-pyridyl borane that can effectively couple to a wide range of aryl and heteroaryl halides and pseudohalides has evaded the synthesis community for decades. The discovery that Cu(DEA)₂ powerfully enables palladium-mediated cross-couplings with air-stable boronates 1 has finally provided a general solution to this problem. DEA=diethanolamine, DMF=N,N′-dimethylformamide, Tf=trifluoromethanesulfonyl.

pH values go live! A ratiometric two-photon (TP) probe (NP1, see scheme) that has a significant TP action cross-section, high photostability, negligible toxicity, and can estimate pH values in live cells and human tissues by two-photon microscopy is described. NP1 can detect the difference in pH between live cells from the gastroesophageal junction (GEJ) and the lower esophageal sphincter of patients with and without esophagitis (see image).

A bright combination: A new type of donor–acceptor dyad, carbazolylaryl-substituted ortho-carboranes, which are conveniently prepared from the corresponding acetylenes and decaborane pathways, showed unique excited-state behavior associated with electron transfer unlike the meta- and para-counterparts (see picture).

They “know” where to go: A powerful orientation effect has been observed in complexes of mixed organocuprates [R_TR_NTCuLi] and substrates with CC, CN, and CS double bonds (see scheme; Th=thienyl). The preferred geometry of the intermediate complex sets up the facile addition of R_T to the double bond, rather than addition of the “dummy ligand”, R_NT.

Bio-logic-al: An autonomous, integrated “sense-act-treat” system that is based on an enzymatic biofuel cell has been developed. The system couples a biocomputing logic-detection method with a drug-release system to provide a logic-activated therapeutic intervention in response to a simulated abnormal physiological state, without the need for an external power source, control electronics, or microelectromechanical actuators.

Snipping tool: The rhodium(I)-catalyzed extrusion of carbon monoxide from biaryl ketones and alkyl/alkenyl aryl ketones was developed to produce biaryls and alkyl/alkenyl arenes, respectively, in high yields (see scheme). A wide range of functionalities are tolerated. Not only does this method provide an alternative pathway to construct useful scaffolds, but also offers a new strategy for CC bond activation.

We have contact! Material strain can have a dominating effect on contact electrification. When a deflated (relaxed) balloon is rubbed against teflon, the teflon surface charges positively, but when the same balloon is inflated (strained), the teflon surface charges negatively. This result illustrates that material strain can control contact electrification and alter the driving force of some (yet unknown) charge-transfer species.

Rapid and direct: The carboxylation of boronic acid esters with ¹¹CO₂ provides [¹¹C]carboxylic acids as a convenient entry into [¹¹C]esters and [¹¹C]amides (see scheme). This conversion of boronates is tolerant to diverse functional groups (e.g., halo, nitro, or carbonyl).

Vinylallenes or cross-conjugated trienes are obtained selectively in the title reaction (see scheme). Two possible mechanisms are suggested to rationalize the formation of the different types of products. Control experiments indicate that p-benzoquinone (BQ) plays an important role as a ligand in addition to its role as an oxidant. E=CO₂Me.

Chiral acids: A highly enantioselective iridium-catalyzed hydrogenation of β,γ-unsaturated carboxylic acids is developed for the preparation of chiral 4-alkyl-4-aryl butanoic acids (see scheme).

Chameleon: A new strategy for the synthesis of a wide variety of alkynyl derivatives by the reaction of substituted arylsulfonylacetylenes with organolithium species is described (see scheme). The high yields, the simplicity of the experimental procedure, the broad scope of this reaction, and the formation of C_spC bonds without using transition metals are the main features of this methodology.

A copper-catalyzed asymmetric allylic boronation (AAB) gives access to syn- and anti-1,2-diols. The method facilitates an iterative strategy for the preparation of polyols (see scheme), such as the fully differentiated L-ribo-tetrol and protected D-arabino-tetrol. P=protecting group

Strolling the ring: A general regioselective directed peri(C4)-metalation route to 1 through an in situ N-anionic protection of C2 is reported. The azaindoles may be elaborated by directed ortho metalation (DoM) and Suzuki coupling to more complex heterocyclic systems. An iterative ring-walk DoM sequence furnishes the exhaustively substituted 2. DMG=directed metalation group, TMEDA=N,N,N′,N′-tetramethylethylenediamine, TMS=trimethylsilyl.

A rapid solvothermal approach was used to synthesize aligned 1D single-crystal rutile TiO₂ nanowire (NW) arrays on transparent conducting substrates as electrodes for dye-sensitized solar cells. The NW arrays showed a more than 200 times faster charge transport (see picture) and a factor four lower defect state density than conventional rutile nanoparticle films.

Fast data collection: A general method for dual data acquisition of multidimensional magic-angle spinning solid-state NMR experiments is presented (see picture). The method uses a simultaneous Hartmann–Hahn cross-polarization from ¹H to ¹³C and ¹⁵N nuclei and exploits the long-living ¹⁵N polarization for parallel acquisition of two multidimensional experiments.

Rh COT in the act: A Ni⁰-catalyzed [2+2+2+2] cycloaddition provides a high-yielding, scalable synthesis of the ligand dinaphtho[a,e]cyclooctatetraene (dnCOT). dnCOT complexation with Rh^I gives [Rh(dnCOT)(MeCN)₂]SbF₆ (see scheme), an excellent catalyst for [5+2] cycloadditions of vinylcyclopropanes and π-systems with impressive functional group compatibility.

In the right light: UV light triggers bond breaking, liberates a caged carboxylic acid, and generates the central CC double bond in the photoresponsive hexatriene molecule of a dithienylethene molecular switch. Light of the same wavelength converts the colorless isomer into its colored counterpart (see picture) in a visually convenient method to report on the success of the release event.

Sustainable Oxidations: An oxidation method to transform aryl(di)azinylmethanes into aryl(di)azinyl ketones is described. Base metals (copper and iron) as catalysts in combination with O₂ as the oxidant are used, which makes this method sustainable. The utility of this method is illustrated by the synthesis of 6-(4-methylbenzoyl)pyridine-2-carbaldehyde, which is an intermediate in the preparation of the drug Acrivastine.

Marine macrolides: An improved second-generation total synthesis of the anticancer macrolide spirastrellolide A methyl ester has been achieved. The synthesis features a uniformly high level of stereocontrol combined with more expedient fragment assembly, and demonstrates a critical dependence of the crucial macrolactonization step on the substitution pattern of the C22–C24 linker region.

Eliminating restraints: A trigonal-bipyramidal structure has been found to be the energetically favored geometry of the hypervalent AX₅ molecule Sb(C₆F₅)₅ in the solid state and also in fluid solution, where molecules move freely and no crystal packing effects operate (see picture).

Think before you act: A computational approach is reported for evaluating the synthetic potential of heterocyclic arynes. Routine and rapid calculations of arene dehydrogenation energies and aryne angle distortion predict the likelihood that a given hetaryne can be generated, as well as the degree of regioselectivity expected in a reaction between a given hetaryne and a nucleophilic trapping agent (see picture).

Quite select: A new strategy was developed for the synthesis of various oxindoles from carbamoyl chlorides. Under the optimum reaction conditions, with Ad₂PBu as a ligand, tBuCONHOH as an additive, and a CO atmosphere, selective C(sp³)H activation proceeded in the presence of a C(sp²)H bond. Ad=adamantyl.

Under the surface: Ag nanoparticles are deposited onto the surface of commercially available SiO particles, and subsequent chemical etching results in the formation of nanoporous SiO (see picture) without changing the chemical and physical properties of the original SiO. Moreover, chemical-assisted thermal annealing produces a shape-preserving Si-based multicomponent system, which exhibits high-performance electrochemical properties.

There and back again: Hydrogenation of esters and the reverse reaction of dehydrogenative coupling of alcohols are efficiently catalyzed by dimeric complexes of Ru and Os under neutral conditions. The Os dimer (see picture) is an outstanding catalyst for the hydrogenation of alkenoates and triglycerides, and allows production of fatty alcohols from olive oil. This complex converts ethanol into ethyl acetate and hydrogen under reflux.

Highly selective: The title reaction is achieved with high enantiomeric and geometric control and thermodynamically unstable (Z)-enone derivatives are obtained as the major products (see scheme). The procedure tolerates a wide range of substrates to generate optically active pyrazolones with vinyl-substituted quaternary stereocenters.