Angewandte Chemie International Edition

In situ molecular-level studies of catalytic reactions with scanning tunneling microscopy (STM) and sum frequency generation (SFG) vibrational spectroscopy have revealed seven molecular components of selectivity—surface structure, adsorbate-induced restructuring, adsorbate mobility, reaction intermediates, surface composition, charge transport, and oxidation states—for heterogeneous catalysis on metal single-crystal model surfaces and nanoparticles. For details, see the Review by G. A. Somorjai and J. Y. Park on page 9212 ff.

The cycle of formation and breakup of iridium clusters from mononuclear iridium diethylene complexes anchored in dealuminated Y zeolite is demonstrated by B. C. Gates and co-worker in their Communication on page 9245 ff. The picture represents the chemistry of cluster formation and breakup (a cycle, as the progress is reversible), with a background of the zeolite cage in which the chemistry takes place.

The Catalysis Society of Japan (CATSJ) celebrates its 50th anniversary this year. A brief history, summary of its activities, and outlook is presented.

Dynamic duo: Combined spectroscopy and microscopy techniques now allow the nature of active sites on zeolite catalysts to be determined in detail. For example, synchrotron IR microscopy reveals the dimeric carbocation of 4-fluorostyrene in a single crystal of ZSM-5 (see picture).

A great support act at the Palladium: In the search for an alternative to the current indirect industrial synthesis of H₂O₂, small nanoparticles of Au–Pd alloys have been shown to be highly active catalysts for the direct synthesis of H₂O₂ from O₂ and H₂. They do not require the addition of halide and phosphate stabilizers. The active particles comprise mainly Pd (blue, see picture) with some Au (green) supported on carbon (red).

Wood, a renewable energy source, can be converted into fuels, chemicals, and energy products. An overview is presented of the processing of lignocellulose-rich starting materials into BTL (biomass-to-liquid) fuels, describes the complex reactions that take place at the porous catalysts in a biorefinery, and brings to light the challenges involved in the transition from pilot to production plants.

The magnificent seven: The selectivity of heterogeneous catalyst processes has been defined on the molecular level by seven factors (see picture). These include the structure and the electronic properties of the surface, the type and mobility of the adsorbed species, as well as the charge transport and oxidation states of the catalyst.

D'you know what amine? Primary and tertiary amines are both immobilized on the same silica–alumina surface by silane-coupling reactions. The resultant silica–alumina-supported double-amines are found to exhibit excellent catalysis for 1,3-dinitroalkane synthesis from various aldehydes with nitromethane. A cooperative catalytic mechanism on the solid surface for this efficient synthesis is proposed.

Diels or no Diels? A bifunctional organic catalyst based on the thiourea motif is able to coordinate both diene and dienophile in an unprecedented asymmetric Diels–Alder reaction of 3-vinylindole derivatives, giving a rapid access to optically active tetra- and hexahydrocarbazoles with excellent results in terms of yields, diastereoselectivities, and enantioselectivities.

Catalyst support: The first highly enantioselective heterogeneous hydrogenation of aromatic ketones catalyzed by Ir/SiO₂ stabilized with Ph₃P and modified by a chiral diamine derived from a cinchona alkaloid is described (see scheme). The reaction can be employed for the reduction of a broad range of aromatic ketones to the corresponding alcohols with high enantioselectivity.

The chemistry of formation of iridium clusters from mononuclear iridium diethylene complexes anchored in dealuminated Y zeolite, and their subsequent breakup—all including changes in the metal–metal, metal–support, and metal–ligand interactions—is demonstrated by time-resolved EXAFS, XANES, and IR spectroscopy.

Supporting green chemistry: The supported ruthenium hydroxide Ru(OH)_x/Al₂O₃ acts as an efficient heterogeneous catalyst for the oxygenation of primary amines to primary amides (see scheme). Various primary amines (including aromatic, aliphatic, and heterocyclic) are converted in aqueous media, using air as the sole oxidant and producing only water as a by-product.

Ru experienced? Two novel coordinatively unsaturated SiO₂-supported Ru complexes were prepared by photoinduced ligand elimination, accompanied by dissociative coordination of a surface OH group to the unsaturated Ru center by photoirradiation. Wavelength- and atmosphere-dependent photoinduced reversible interconversion occurs between the two Ru complexes. One of the complexes is catalytically active for the photooxidation of cycloalkanes with O₂.

What, where, when: A combination of both surface-sensitive (diffuse reflectance infrared Fourier transform spectroscopy, DRIFTS) and bulk-sensitive (Raman spectroscopy) detection at different catalyst-bed positions is shown to be a powerful tool to facilitate deeper understanding of complex dynamic surface and bulk processes, which occur widely in heterogeneous catalysis.

High activity is generated by sudden formation of disordered oxidic platinum over a platinum catalyst supported on alumina (see picture). High temperature and low concentration of carbon monoxide are required to generate high activity.

Not all that glitters… The activity of supported gold nanoparticles depends on the method used for their preparation. Gold clusters of about 2 nm in diameter were deposited on nonreducible metal oxides and carbon materials by solid grinding of a volatile organogold complex in a ball mill and subsequent calcination (see scheme). Au/ZrO₂ and Au/Al₂O₃ prepared in this way were extremely efficient catalysts for the aerobic oxidation of glucose.

A flexible friend: The electronic and structural changes undergone by Cu sites grafted inside an amorphous nanoporous P4VP matrix during a simple redox process (representing more complex liquid-phase catalysis) were investigated by complementary in situ techniques (FTIR, UV/Vis, XAS spectroscopy) (see scheme; brown Cu, green Cl, blue N, red O). The flexibility of the polymeric structure was found to be the key factor in the reversibility of the redox process.

Alkynes of everything: Fundamental differences in the palladium-catalyzed hydrogenation of double and triple CC bonds arise from marked differences in the composition of the catalyst surface. In situ X-ray photoelectron spectroscopy of the near-surface region of active palladium catalysts uncovers strong links between the chemical nature of the (alkyne/alkene) reactive molecules and the subsurface state of the catalyst (I–IV).

Tubular Al's: Quantum chemical calculations show the facile formation of nanotubular methylaluminoxanes from reactions between water and trimethylaluminum. The nanotubular methylaluminoxane is shown to be capable of activating metallocene catalysts for α-olefin polymerization (see structure; red O, bronze Al, blue Zr).

Robotlike: Low catalyst loadings of a planar-chiral ferrocenyl bispalladacycle are sufficient to catalyze the Michael addition of trisubstituted α-cyanoacetates to enones with excellent yields (TONs up to 2450) and high enantioselectivity. The reaction proceeds by a cooperative bimetallic mechanism and is superior to previous methods relying on soft Lewis acid catalysts.

The mechanism of olefin hydrogenation on a supported noble-metal catalyst requires the presence of weakly bound hydrogen atoms absorbed in the volume of the metal particle (see picture). Co-adsorbed carbonaceous deposits affect the hydrogen distribution in the metal clusters and critically control their activity and selectivity in olefin conversions.

Chiral rhodium(I) complexes activate allenyl tert-cyclobutanols efficiently through enantioselective insertion into a CC σ bond of the cyclobutane (see scheme; cod=1,5-cyclooctadiene, DTBM=3,5-di-tert-butyl-4-methoxyphenyl). Ring expansion by this method produced cyclohexenones with quaternary stereogenic centers with excellent enantioselectivity. The catalyst loading can be decreased to just 0.1 mol % in rhodium.

Summing Me up: DFT calculations have shown that alloying, subsurface carbon, and hydride formation, all increase the selectivity of Pd catalysts for acetylene hydrogenation by weakening the surface–adsorbate bond. A simple descriptor—the adsorption energy of a methyl group—has been used to quantify and compare the different effects in the adsorption of acetylene and ethylene on various transition-metal surfaces (see picture).

Dynamic observation: The rapid oxidative redispersion of large Pt nanoparticles supported on ceria-based oxide in autoexhaust catalysts is demonstrated in the absence of Cl by in situ XANES analysis. An atomic migration model accounts for the observed redispersion through the trapping of Pt species at sites on the Ce support that exhibit strong interactions between the Pt oxide and the support.

A volcano curve is observed for the hydrogen oxidation reaction (HOR) as a function of the Pd content of alloyed PtPd electrodes. The maximum exchange current density was obtained for Pt₇₂Pd₂₈, and the results indicate that PdH_x species (hydrogen gas spontaneously adsorbed to Pd; see picture) causes the electronic structure of Pt to be favorable for the HOR.

A means to an end: Polyethylene chains obtained by catalyzed chain growth on magnesium and exhibiting molar masses up to 5000 g mol⁻¹ have been end-functionalized in high yield with iodide, azide, and amine reactive end groups (see scheme). The functionalized polyethylenes can be used to generate a range of reactive polyolefins; for example, the azide-functionalized chain can undergo “click” reactions to afford macromonomers.

A simple thermal treatment remarkably enhances the activity and durability of CuFe₂O₄–Al₂O₃ composite catalysts in reforming dimethyl ether for hydrogen production. The most effective treatment temperature range is 700 to 800 °C. The active phase, CuFe_1.5Al_0.5O₄ formed through a solid-state reaction between CuFe₂O₄ and Al₂O₃, and the original phase, CuFe₂O₄, contribute synergistically to the enhancement.

Come on allene: Commercially available [Re₂(CO)₁₀] as a catalyst provides five-membered carbocycles in moderate to excellent yields with high stereoselectivity (see scheme). The configuration at each of the three sp³ carbon centers of the ring is defined. The reaction proceeds at the β, γ, and adjacent methylene positions of the allene; previously, similar reactions usually occurred at the α, β, and γ positions of the allene.

Enzyme in action: Labeling studies and the finding that carboxymethylproline synthase catalyzes production of deuterated (2S,5S)-6,6′-dimethyl-trans-carboxymethylproline (3) from dimethylmalonyl-CoA (1) and labeled l-pyrroline-5-carboxylate (2) limit possible mechanisms of CC bond formation and thioester hydrolysis. A key feature in the catalysis is that intermediates are stabilized by hydrogen bonds in the “oxy-anion hole” of the enzyme (dark curve in scheme).

Catalysts with a bite: Chiral Pd^II complexes were prepared with tridentate N-heterocyclic carbene amidate alkoxide ligands. Dimeric and monomeric forms were mutually convertible by acid or base treatment (see scheme). The catalysts promote asymmetric Heck reactions efficiently, offering high enantioselectivities far superior to those of existing methods.

Setting the TEMPO: The scheme shows the efficient aerobic synthesis of 2-substituted benzoxazoles, benzothiazoles, and benzimidazoles where 4-methoxy-2,2,6,6-tetramethyl-1-piperidinyloxy free radical (4-Methoxy-TEMPO) is used as the catalyst.

Mild thing: The first nickel-based catalysts for cross-couplings of secondary organometallic nucleophiles with secondary alkyl electrophiles have been developed. Thus, Negishi reactions proceed under mild conditions (at room temperature with no basic activators) in the presence of NiCl₂⋅glyme and a tridentate ligand (see scheme).

All for one: A combination of three biocatalysts (ω-transaminase, alanine dehydrogenase, and an enzyme such as formate dehydrogenase for cofactor recycling) catalyze a cascade to achieve the asymmetric transformation of a ketone into a primary α-chiral unprotected amine through a formal stereoselective reductive amination (see scheme). Only ammonia and the reducing agent (formate) are consumed during this reaction.

Splitting water: Oxygen-permeable perovskite hollow-fiber membranes are used to produce hydrogen and synthesis gas from water and methane (see picture). The process yields valuable compounds, and provides insight into the interplay of catalysis and separation in a membrane reactor.

A sweet conversion! A NHC–Cr/ionic liquid system has achieved excellent efficiency and the highest 5-hydroxymethylfurfural (1; see scheme; NHC=N-heterocyclic carbene) yields reported thus far for both fructose and glucose feedstocks. The catalyst and ionic liquid are tolerant of high substrate loading and can be recycled after extraction of the product.

Turbo nanomotors: A dramatic increase of the speed of fuel-driven nanowire motors is obtained using an Ag/Au alloy segment. These nanomotors offer speeds as high as 150 μm s⁻¹ (75 body lengths per second), approaching those of the most efficient biomotors. The increase in the fuel decomposition rate associated with the electrochemical reactivity of Ag/Au alloys will enable the design of energy-efficient nanomotors.