Chemistry – An Asian Journal

150 years of German–Japanese friendship was celebrated last year. This issue of Chemistry – An Asian Journal is a special issue dedicated to the occasion. It features top contributions from around the world, including an Essay on the development of biocatalytic processes in both countries, Focus Reviews on molecular spintronics and nonlinear optical properties of confined dyes, as well as over 30 original research papers. The cover picture by Kazuyuki Tatsumi et al. highlights the connection between Germany and Japan, just as the two iron centers in an anthracene double sandwich complex are electronically coupled, as reported by this group as a Full paper on page 1231 ff.

The twin catalytic capabilities of an aqueous phase hydrogenase mimic are illustrated. As described in their Full paper on page 1394 ff., Seiji Ogo et al. report that a very small change in the ligand system switches the catalyst between dihydrogen activation, to produce protons and electrons, and dioxygen activation, to produce reduced oxygen species. The harmonious blending of these two cycles opens up a new field in fuel cell catalysis by providing a starting point for future molecular catalysts. In addition, the crystal structure of the oxygen-bound catalyst gives an insight into the acquisition of oxygen tolerance by some NiFe hydrogenases.

Long tradition: Germany and Japan have long collaborated in the field of biocatalysis, driving industrial innovation in both countries. Biocatalysis first found its way into the chemicals industry by way of microbial processes. Further developments used isolated enzymes and tailor-made enzymes and cells for a range of processes that gave high conversion, optical purity, and space–time yield. Up to now, a broad range of industrialized biocatalytic processes have been developed in both countries (see scheme for selected products), which are summarized in this essay.

I'm spinning around: This review summarizes the switching of the Kondo signal for [TbPc₂] single-molecule magnets (SMMs) on Au(111), which is a spin one-half Kondo system owing to the ligand spin. The upper ligand can be rotated in a controlled manner, thereby switching the ligand spin on and off. Thus, information can be encoded at the single-molecular level by controlling the molecular spin through an electric current.

No feet of clay: Hybridization of organic chromophores with clay minerals maximizes nonlinear optical responses of the chromophores. Such hybrid materials were previously unsuitable as optical materials due to considerable light scattering. However, recent progress in the fabrication of hybrids has enabled the generation of low light-scattering self-standing films of clay/dye hybrids suitable for nonlinear optical devices.

Triple stack: A facile synthesis of charge-transfer-type crystals composed of CTV and POM was demonstrated. The crystals further accommodated 1,4-benzoquinone as a guest to form a ternary crystal with a donor–acceptor–acceptor arrangement. The electronic spectra of the crystals suggested that the incorporated quinone served as an electronic modulator to adjust the charge-transfer property.

Proacetylenic: An aniline-based donor–acceptor-substituted butatriene exhibits not only cumulene-like dimerization to give a [4]radialene (λ_max=756 nm), but also acetylene-like (proacetylenic) reactivity towards tetracyanoethene, affording via [2+2] cycloaddition–cycloreversion a NIR-absorbing zwitterionic chromophore (λ_max=825 nm). The cationic charge on the imminium-type nitrogen in the zwitterion is evidenced by host–guest complexation with a tetraphosphonate cavitand.

Two birds with one stone: Magnesium-base-catalyzed highly diastereoselective direct-type aldol reaction of glycine Schiff base bearing a fluorenylidene moiety as a protecting and activating group was developed. The desired reactions proceeded smoothly at low temperature, and the aldol products were obtained in high yield with high diastereoselectivity.

Enantioselective calcium-catalyzed addition reactions of styrene and indole derivatives with trifluoropyruvates have been developed. The alkaline-earth metal-catalyzed reactions proceed smoothly to afford the corresponding products in high yields and with good to excellent enantioselectivities under mild reaction conditions.

A general palladium-catalyzed carbonylative dimerization of styrenes has been developed. Starting from commercial available styrenes, symmetrical 1,5-diarylpent-1-en-3-ones were produced in good to excellent yields (see scheme; dppp=1,3-bis(diphenylphosphino)propane).

Teaching metalloenzymes new tricks: An artificial type III dicopper oxidase has been developed using a hydrolytic enzyme, metallo-β-lactamase, as a metal-binding platform. The triple mutant D88G/S185H/P224G redesigned by computer-assisted structural analysis showed spectroscopic features similar to those of type III copper proteins and exhibited a high catalytic activity in the oxidation of catechols under aerobic conditions.

Undirected/Directed Cross-Coupling: A new dehydrogenative Rh^III-catalyzed cross-coupling reaction between bromoarenes bearing no directing group and vinylic substrates substituted by a chelating group is reported. An original reaction mechanism enables the use of internal alkenes in a Z-selective coupling. The application of 1,3-disubstituted or 1,2-homodisubstituted arenes leads to the formation of highly functionalized, complex, and valuable olefins as one single isomer.

Wanted—Dead or Alive: The reactions of cationic transition-metal hydrides MH⁺ of the first row with ammonia have been studied both experimentally and computationally. All ions investigated are wanted; they don′t spare ammonia and react predominantly under NH bond activation (Sc, Ti, Cr), ligand exchange (Co, Ni), or proton transfer (Mn, Fe, Zn).

Protein phosphatase 2B inhibitor: Optically pure norcantharidin analogue NCA-01, a highly selective inhibitor of protein phosphatase 2B (PP2B), has been synthesized. The PP2B-inhibitory activity of NCA-01 and its derivatives were independent of the enantiomeric form.

Caught in the middle: Dinuclear {(Cp*)Fe^I} complexes (Cp*=η⁵-C₅Me₅) bridged by naphthalene (left) and anthracene (right) were prepared. These complexes exhibited large electrochemical potential separations between successive one-electron redox events and the mixed valence complexes were synthesized by chemical oxidation.

The perfect host: The synthesized iridium- and rhodium-based hexanuclear organometallic cages (figure, left) can form inclusion systems with a wide variety of π-donor substrates. The 1:1 complexation of the resulting supramolecular assemblies were confirmed by ¹H NMR spectroscopy, and the formation of discrete 1:1 donor–acceptor complexes, such as [Pt(acac)₂]⊂6 a (figure, right), were confirmed by their single-crystal X-ray analyses.

A clear view: A catalyst model comprising platinum nanoparticles deposited on a TiO₂(110) wafer was characterized with Kelvin probe force microscopy. The topography and local work function of individual nanoparticles were observed with single-nanometer resolution in a N₂ environment of one atmospheric pressure. The ability of the microscope was demonstrated in observing charge transfer across metal–oxide interfaces even in the presence of vapor.

The counteranion does the job! Reactions of 2-substituted thiophenes with cationic PhPdbipy complexes afforded either the corresponding C(4) or C(5)-phenylated thiophene derivatives depending on the counteranion present. DFT calculations revealed that reactions occur via carbopalladation and not via electrophilic palladation.

Larger than ever before: A huge nuclear ring current—1.53 e per fs—and as a consequence, a gigantic magnetic field—623 Tesla—may be induced by means of a circularly polarized laser pulse that is designed to drive the pseudorotation of the central nucleus of the tetrahedral OsH₄ molecule.

To bend or not to bend: The potential-energy surface of the system involving atoms H, X, and E (X=N–Bi; E=C–Pb) has been studied to answer a number of questions about the geometry of HCN and HNC and the bonding between the group 14 and 15 elements in the heavier analogues of the HCN–HNC system. The results of charge- and energy-decomposition analyses of the systems are presentedfor the charge f.

Sensitive souls: A series of sensitizers for dye-sensitized solar cells features ring-fused thiophene bridges between donor and acceptor moieties. The absorption spectra of the push–pull sensitizers all exhibit intense intramolecular charge transfer bands in the visible region (see picture), and solar cells based on the dyes show good incident photon to current conversion efficiencies.

Backbone requirements: A series of rare-earth metal bis(dimethylsilylamido) complexes with [OSSO]-type bis(phenolate) ligands [Ln{N(SiHMe₂)₂}₃(thf)_x] (Ln=Sc, x=1; Y, x=2; thf=tetrahydrofuran; see picture) were synthesized and used in the ring-opening polymerization of rac- and meso-lactides.

Py in the sky: Preparation, structural characterization, and redox studies of Ru^III–pyridine-substituted α-Keggin-type silicotungstate hybrid molecules, [SiW₁₁O₃₉Ru^III(Py)]⁵⁻, are reported. Ru^IV was stabilized in silicotungstate.

Make 'em and break 'em: A₂B₆-type [36]octaphyrins were prepared in moderate yields by the cross condensation of tetrapyrromethane with aryl aldehydes. Compounds bearing 2,4,6-trifluorophenyl, 2,6-dichlorophenyl, and phenyl substituents underwent Cu^II-metalation-induced fragmentation to give AB₃-type Cu^II porphyrins, while that bearing a 3-thienyl substituent underwent N-thienyl fusion to provide a modestly aromatic [38]octaphyrin (see scheme).

Off the beaten path: Some frustrated Lewis pairs (FLP) react with unsaturated ketones and esters by means of conjugate addition to the activated carbon–carbon double or triple bond to give the respective P/B addition products. This is different from the FLP reactivity towards, for example, cinnamaldehyde, where 1,2-addition to the carbonyl group is observed.

Less is more: Pyridine, pyrazine, quinoline and related electron-deficient N-heteroarenes can be arylated at the most electrophilic site using organozinc reagents through nickel catalysis. This protocol serves as a complementary method to catalytic direct arylation reactions.

Nuked catalysts! Nanosized platinum particles loaded on TiO₂ (Pt–TiO₂) were synthesized by using a microwave-assisted deposition method with the aim of developing a highly efficient photocatalyst for the decomposition of aqueous NH₃ into H₂ and N₂ in a stoichiometric molar ratio under inert conditions (see picture).

The choice of protecting groups decides about the stereochemical fate of the intermediate benzylic carbocation formed in the reactions of substrates 1. If the ester group is significantly bulkier than the amino group, syn-products (syn-2) prevail. If the size of the amino group is increased by dibenzylation and the ester group is small, the respective anti-products (anti-3) are formed with significant diastereoselectivity.

Tri(thio) Lanes Express: The reactions of two unsymmetrical 1,2,4-trithiolanes with phosphane Pt⁰(η²-nbe) complexes were studied. Based on kinetic measurements of the thermally induced fragmentation of a six-membered platinacycle by using UV/Vis spectroscopy along with DFT-calculations, a refined mechanism for the reactions of [Pt⁰(PPh₃)₂(η²-nbe)] with 1,2,4-trithiolanes was proposed.

At the flick of a switch: A [NiRu] biomimetic system for O₂-tolerant [NiFe]hydrogenases was constructed. Electron donation to the [NiRu] center switched the system between activation of H₂ and O₂. Furthermore, a [NiRu]–peroxo species, which was capable of oxidizing p-hydroquinone, was considered as a biomimetic analogue of O₂-bound species (OBS) of O₂-tolerant [NiFe]hydrogenases.

Quantifying Electrophilicity: Kinetics of the reactions of 1,1-bissulfonyl-ethylenes with carbon nucleophiles have been determined to integrate these Michael acceptors in our comprehensive electrophilicity scales and to compare them with other electrophiles. The electrophilicities depend only slightly on conformational restrictions, and as a rule of thumb, one can assume that two geminal phenylsulfonyl groups exert a similar activation as one nitro group.

Silyl smooth transitions! Hydrogen migration between the tungsten center and the silylene ligand or acetone molecule coordinated to the silylene ligand occurred extensively in hydrido(hydrosilylene)tungsten complexes. WH/SiH exchange, α-H abstraction, hydrosilylation, and CO bond cleavage in the reaction with acetone were all regarded to be driven by the strong Lewis acidity of the silylene ligand (see scheme).

A pinch of proton: Pincer-type ruthenium complex 1 featuring two proton-delivering pyrazole arms underwent sequential deprotonation to afford 3, which was further converted into side-on peroxo complex 4 and end-on dinitrogen complex 5. Dinuclear complex 6 with a less hindered pincer ligand was also synthesized.

Tuning organometallic dyes: The synthesis, characterization, and photovoltaic properties of a new series of unsymmetric platinum(II) bis(aryleneethynylene) photosensitizers (see Figure) for dye-sensitized solar cells are described. The incorporation of a strongly electron-donating group significantly enhances the absorption abilities of the complexes. A power conversion efficiency of up to 1.57 % was achieved under illumination of an AM 1.5G solar cell simulator.

The famous five: The one-pot reaction of readily available N-propargylamides and azodicarboxylates provided functionalized oxazoles through a five-step cycloisomerization/Alder-ene reaction pathway.

The (Ambi)Polar Express: A newly designed ambipolar material, CZBDF, was synthesized. CZBDF possesses a wide-gap character, well-balanced and high hole and electron mobilities of larger than 10⁻³ cm² V⁻¹ s⁻¹, and a high thermal stability. This material functions as an emissive material and a host material for OLEDs and enabled us to produce heterojunction as well as p-i-n homojunction OLED devices that emit full-color visible light with high efficiency.

Get into position: A series of porphyrin—fullerene conjugates have been synthesized and studied in both nonaqueous and aqueous solutions. The microenvironment around the redox-active components has been altered through varying the topology of the dendrimers attached to the porphyrin (see scheme). Photophysical and chemical investigations provide insights into the effect that this has on electron transfer.