Volume 67, Issue 10

With the growing perception of industrialized societies that fossil raw materials are limited resources, academic chemical research and chemical industry have started to introduce novel catalytic technologies which aim at the development of economically competitive processes relying much more strongly on the use of alternative carbon feedstocks. Great interest is given world-wide to carbon dioxide (CO 2 ) as it is part of the global carbon cycle, nontoxic, easily available in sufficient quantities anywhere in the industrialized world, and can be managed technically with ease, and at low cost. In principle carbon dioxide can be used to generate a large variety of synthetic products ranging from bulk chemicals like methanol and formic acid, through polymeric materials, to fine chemicals like aromatic acids useful in the pharmaceutical industry. Owing to the high thermodynamic stability of CO2, the energy constraints of chemical reactions have to be carefully analyzed to select promising processes. Furthermore, the high kinetic barriers for incorporation of CO 2 into C-H or C-C bond forming reactions require that any novel transformation of CO 2 must inevitably be associated with a novel catalytic technology. This short review comprises a selection of the most recent academic and industrial research developments mainly with regard to innovations in CO 2 chemistry in the field of homogeneous catalysis and processes. Graphical Abstract Carbon Dioxide as a Carbon Resource – Recent Trends and Perspectives

Aptamers are single-stranded oligonucleotides composed of RNA or DNA that are able to bind their corresponding targets via molecular recognition. Thus, aptamers can be thought of as nucleic acidbased alternatives to antibodies and have attracted attention as receptors in biosensors. Aptamers seem to be ideal biological recognition elements, since they enable the design of intelligent sensors based on their specific properties. Especially the fact that most aptamers undergo conformational changes during the binding of the target and their oligonucleotide nature can be used to rationally design novel sensing strategies. This review focuses on aptasensors for the detection of small molecules. In the first part, aptamers, their generation and their properties are briefly described. In the second part, different design strategies for aptasensors are reviewed, and examples for the detection of small molecules are given. Graphical Abstract Aptasensors for Small Molecule Detection

The intramolecular frustrated P/B Lewis pair Mes 2 PCH 2 CH 2 B(C 6 F 5 ) 2 (7) reacts readily with phenylsilane by heterolytic cleavage of the Si-H bond to give the zwitterion [Mes 2 (PhH 2 Si)P+CH 2 CH 2 B-H(C 6 F 5 ) 2 ] (8a), which has been fully characterized and its structure confirmed by X-ray crystal structure analysis. Variable-temperature NMR studies revealed that the reaction is reversible. Adduct 8a is the predominant species (ca. 98%) in CD 2 Cl 2 solution at low temperature (193 K), whereas at ambient temperature (299 K) it exists in a ca. 7 : 3 equilibrium with unreacted 7 and PhSiH 3 . Diphenylsilane reacted similarly with the frustrated Lewis pair 7, however, the equilibrium was found to favor the starting materials in the investigated temperature range. Graphical Abstract Reversible Heterolytic Si–H Bond Activation by an Intramolecular Frustrated Lewis Pair

Enzyme catalysis in two-phase systems, particularly in the functionalization of siloxanes, is a new challenge for biocatalysis. On the basis of three different reaction systems, stirred tank reactor, enzyme membrane reactor and micro mixer, the influence of the phase boundary layer along the interface between an aqueous system and an organosiloxane on the synthesis of hydroxyalkylfunctionalized siloxanes is discussed and solutions presented. Micro mixers produce, through a large surface area to volume ratio, boundary layers within which through a formate dehydrogenasecatalyzed reaction the conversion of 1,3-bis-(3-formoxypropyl)tetramethyldisiloxane to 1,3-bis-(3- hydroxypropyl)tetramethyldisiloxane can be achieved. In contrast, in a stirred tank reactor even after 96 h only 45% of the formoxy siloxane has been converted. Graphical Abstract The Boundary Layer as Reaction Compartment for the Synthesis of Hydroxyalkyl-functionalized Siloxanes

Infrared spectroscopy in combination with a specially developed attenuated total reflection (ATR) flow cell and multivariate analysis was used for the quantitative analysis of beer and other beverages. IR spectra of samples were obtained in the range from below 1000 cm -1 to 4000 cm -1 and subjected to a multivariate analysis based on calibration sets with laboratory reference standards. In the case of beer, this calibration set included 240 beer samples spanning the entire range of ethanol content, extract and CO 2 . Based on this calibration, an infrared and UV/Vis spectroscopy-based sensor for the quick and quantitative quality control of beer was developed and subjected to extensive tests in breweries. This sensor meets and exceeds all requirements from brewers for the routine control in the production and bottling. Its use for other beverages, for example wine, juices or apple wine, requires only another set of calibration data for the specific beverage. Graphical Abstract The Good Vibrations of Beer. The Use of Infrared and UV/Vis Spectroscopy and Chemometry for the Quantitative Analysis of Beverages

Crystalline silica shows strong, sharp signals at about 77 and 130 cm -1 in the inelastic neutron scattering spectrum that are missing or strongly different, broadened and shifted to lower frequency for the case of precipitated and fumed silica. The presence or absence of these signals is a sensitive signature of crystallinity or amorphicity in silica. The low-frequency phonon density of states of precipitated and fumed silica is typical for completely amorphous materials. This observation is in perfect agreement with data from X-ray diffraction and high-resolution transmission electron microscopy. The amorphicity is retained during granulation post-treatments. Graphical Abstract Low-frequency Vibrational Dynamics of Amorphous and Crystalline Silica

The enantioselective synthesis of 2-aryl-substituted 2,3-dihydroquinolin-4-ones, a class of heterocyclic compounds with interesting biological activities, has been achieved through a Brønsted acidcatalyzed enantioselective intramolecular Michael addition. The products are available in moderate to high yields and with good enantioselectivities. Graphical Abstract Asymmetric Brønsted Acid-catalyzed Intramolecular aza-Michael Reaction – Enantioselective Synthesis of Dihydroquinolinones

Graphical Abstract Synthesis and Characterization of Imidazolium Salts with the Weakly Coordinating [B(C 6 F 5 ) 4 ] – Anion

12-Keto-UDCA is an important optically active component for the drug ursodeoxycholic acid (UDCA). Starting from the three-keto compound dehydrocholic acid, the carbonyl groups at position 3 and 7 have to be reduced stereo- and regioselectively. In this case we applied two hydroxysteroid dehydrogenases for this purpose, the NAD-dependent 3α-HSDH from Pseudomonas testosteroni and the NADP-dependent 7β-hydroxysteroid dehydrogenase from Collinsella aerofaciens. Both enzymes can be produced in high yields by an Escherichia coli strain as recombinant proteins. In order to avoid impurities by the 7a-hydroxysteroid dehydrogenase of Escherichia coli, a mutant strain with an inactivated 7a-enzyme was applied for producing the three enzymes. For bioconversion, the dehydrogenases can be used as crude enzyme samples and are applied simultaneously. A 1.8 L batch of 100mM DHCA incubated at pH = 8.0 and 25°C resulted in 80 g crude product with a quite high purity of ≥ 99:5% as judged by HPLC analysis. Graphical Abstract Large-scale Enzymatic Synthesis of 12-Ketoursodeoxycholic Acid from Dehydrocholic Acid by Simultaneous Combination of 3α-Hydroxysteroid Dehydrogenase from Pseudomonas testosteroni and 7β-Hydroxysteroid Dehydrogenase from Collinsella aerofaciens

The Asinger reaction is a very powerful tool to form 2,5-dihydro-1,3-thiazoles in high yields. Treating these heterocyclic imines with acid chlorides followed by adding sodium carboxylates led to a large number of new O,N-diacyl O,N-acetals. Using chiral starting materials, a high diastereoselectivity was observed in several cases. X-Ray structures document the constitution and clarify the relative configuration of the prepared O,N-diacyl O,N-acetals. Graphical Abstract 2,5-Dihydro-1,3-thiazoles as Scaffolds in the Synthesis of O,N-Diacyl O,N-Acetals in a One-pot Reaction

Limonene is an industrially interesting monoterpene that accumulates in bulk quantities as byproduct of the fruit juice industry. The corresponding epoxides are versatile synthetic intermediates and additives for the chemical industry. Due to a number of disadvantages of classical chemical epoxidation including serious safety issues and unwanted side-reactions, we here used a mild lipasecatalyzed chemo-enzymatic epoxidation system, with either free or different immobilized forms of Candida antarctica lipase B. Full limonene conversion (> 98%) was easily achieved at 40°C within less than 24 h. The enzymatic activities in the formation of limonene monoxide significantly varied from either 1 - 3:4 U/mg biocatalyst at r. t. or from 1.7 - 4:9 U/mg biocatalyst at 40°C. For the first time we showed that it is possible to generate high amounts of limonene dioxide ( ~ 30% with CalB on carrier 350 at 40°C) using this mild lipase-mediated epoxidation method. Enzyme activities and limonene dioxide yields strongly depend on the nature of the selected enzyme carrier, the immobilization method and the reaction temperature. Graphical Abstract Lipase-mediated Epoxidation of the Cyclic Monoterpene Limonene to Limonene Oxide and Limonene Dioxide

Hydroformylation of 1-butene using a triphenylphosphine-modified iridium catalyst was investigated by operando infrared spectroscopy. The spectra were interpreted by comparison with quantumchemically calculated vibrational spectra at the density functional theory level. The processes during activation of the catalyst and hydroformylation were investigated in detail, and the results are discussed. The recently discovered phenomenon of activity enhancement in iridium-catalyzed hydroformylation by a preceding activation step, in which the reaction mixture is treated with synthesis gas containing an excess of carbon monoxide under pressure, could be correlated with the appearance of a complex HIr(PPh 3 )(CO) 3 . The similarities and differences between iridium- and rhodium-catalyzed hydroformylation are discussed. Graphical Abstract Operando Infrared Spectroscopic and Quantum-chemical Studies on Iridium-catalyzed Hydroformylation

The title compound (H 2 tpsac) was synthesized from 6-bromosaccharin and 3,3’’-bis(bromomethyl)- m-terphenyl. The ability of tpsac to serve as a tetradentate bis-bridging ligand was demonstrated by the formation of the dinuclear ruthenium(I,I) complexes [Ru 2 (CO) 5 (μ,μ-tpsac)] 2 , [Ru 2 (CO) 4 (μ,μ-tpsac)] n , [Ru 2 (CO) 4 (PPh 3 ) 2 (μ,μ-tpsac)], and [Ru 2 (CO) 5 (PPh 3 )(μ,μ-tpsac)]. An X-ray crystal structure analysis of [Ru 2 (CO) 4 (PPh 3 ) 2 (μ,μ-tpsac)] showed the head-to-tail (or 1,1) arrangement of the two saccharinate coordination sites. Graphical Abstract 3,3’’-Bis(saccharin-6-ylmethyl)-1,1’:3’,1’’-terphenyl – Precursor of A New Tetradendate Bis-bridging Ligand

The new methylene-bridged dialuminium compound Aryl 2 Al-CH 2 -AlAryl 2 1b was synthesised from Cl 2 Al-CH 2 -AlCl 2 and four equivalents of LiAryl [Aryl=C 6 H 2 (2,4,6-i-Pr) 3 ]. A 1 : 2 stoichiometric ratio of the starting compounds afforded the dimeric aluminium halide (Aryl 2 AlCl) 2 (2) by dismutation. The coordination behaviour of the related, but more easily available dialuminium compound R 2 Al-CH 2 -AlR 2 [R=CH(SiMe 3 ) 2 ] 1a was explored. It yields the Lewis acid base adducts [M][R 2 Al-CH 2 -AlR 2 (μ-X)] [3a, M=Li(TMEN) 2 , X=Cl; 3b, M=Li(TMEN) 2 , X=Br; 3c, M=K(18-crown-6), X=ClO 4 ; 3d, M=Li(TMEN) 2 , X=NH(i-Pr)] with X residing in a bridging position between the two Al atoms as evident from NMR spectroscopy and X-ray crystallography (3b, 3c, 3d). Compound 3c is a unique example of a stable, in organic solvents soluble adduct that features a ClO 4 - anion coordinated by an alkylaluminium compound via two of its oxygen atoms. Graphical Abstract The Methylene-bridged Dialuminium Compound R 2 Al-CH 2 -AlR 2 [R=CH(SiMe 3 ) 2 ] as an Effective Chelating Lewis Acid – Adducts with Halides, Perchlorate and Isopropylamide

The so far missing chloro analog of the bromofullerene C 2v -C 60 Br 8 has been synthesized by reaction of C 60 fullerene with iodine monochloride. The title compound has been separated by means of HPLC, and its molecular structure has been unambiguously determined by single-crystal X-ray analysis. A facile synthesis of C s -C 60 Cl 6 and C 2v -C 60 Cl 8 in preparative amounts is presented. Graphical Abstract Synthesis, Separation and Structure Elucidation of a Missing C 60 Chloride: C 2v -C 60 Cl 8

The two new thiostannate compounds (trenH) 2 Sn 3 S 7 (1) and {[Mn(tren)] 2 Sn 2 S 6 } (2) (tren=tris-2-aminoethylamine) were obtained under solvothermal conditions. Compound 1 crystallizes in the hexagonal space group P6 3/ mmc with a=13.2642(19), c=19.078(3) Å, V =2906.9(7) Å 3 . The layered [Sn 3 S 7 ] 2- anion is constructed by Sn 3 S 4 semi-cubes sharing common edges. The layers are characterized by large hexagonal pores with dimensions of about 11×11 Å 2 . Compound 2 crystallizes in the triclinic space group P1̄ with lattice parameters a=7.6485(7), b=8.1062(7), c=12.1805(11) Å, α =97.367(11), β =103.995(11), γ = 108:762(10)°, V =676.17(10) Å 3 . The [Sn 2 S 6 ] 4- anion is composed of two edge-sharing SnS4 tetrahedra and joins two Mn 2+ -centered complexes by Mn-S bond formation. The Mn 2+ cation is in a trigonal-bipyramidal environment of four N atoms of the tren ligand and one S atom of the thiostannate anion. Both compounds are semiconductors with a band gap of 2:96 eV for 1 and of 2:75 eV for 2. Graphical Abstract New Thiostannates Synthesized Under Solvothermal Conditions: Crystal Structures of (trenH) 2 Sn 3 S 7 and {[Mn(tren)] 2 Sn 2 S 6 }

Two modifications of EuCu 5 Cd were synthesized from the elements in sealed tantalum ampoules.The high-temperature (HT) modification was obtained from an induction-melted sample that was finally annealed at 873 K, while the low-temperature (LT) phase is formed in a muffle furnace by annealing a pre-melted sample at 673 K. DSC measurements gave a transition temperature of 823±2 K. Both structures were refined on the basis of single-crystal X-ray diffractometer data: R3̄m, a = 511:58(7), c = 3059:6(6) pm, wR2 = 0.0289, 316 F 2 values, 22 variables for HTEuCu 4 :85(1) Cd 1:15(1) and Pnma, a = 2545:6(5), b = 511:60(1), c = 1060:3(2) pm, wR2 = 0.0386, 2044 F 2 values, 121 variables for LT-EuCu 4:92(1) Cd 1:08(1) . A small degree of Cu/Cd mixing was observed for three sites. Both structures adopt new types. The europium atoms have high coordination numbers of 18, 19 and 20 in LT- and 18 and 20 in HT- EuCu 5 Cd. These three types of polyhedra are the basic building units also in the closely related structures of CeCu 6 , CeCu 5 Au, CeCu4:38In1:62, and CeNi 5 Sn, a family of stacking variants. Temperature-dependent magnetic susceptibility measurements of a HT- EuCu 5 Cd sample showed an experimental magnetic moment of 7.56(1) μB per Eu atom in the paramagnetic regime, compatible with divalent europium. HT- EuCu 5 Cd orders antiferromagnetically at 17.7(5) K. Graphical Abstract Dimorphic EuCu 5 Cd

5-Lithiated 4,4-dimethyl-2-(2-thienyl)oxazoline reacted by halide and tetrahydrothiophene (THT) substitution with [AuCl(THT)] to form a cyclic trinuclear compound (1) in satisfactory yield. Spectroscopic studies and single-crystal X-ray analyses clarified the bonding within the ring system. The structure determination of two THF solvates revealed differences in the supramolecular assembly of the constituting molecules. Graphical Abstract 18-Membered Heterometallacyclic Gold(I) Compounds: Structural Influences of Co-crystallized Solvent

Diethyl malonate turned out to be both a “green” and highly efficient acyl donor in the lipase-catalyzed resolution of amines, thus representing an attractive alternative to currently applied acyl donors. By means of this acyl donor a highly efficient enzymatic process for the resolution of amines, running at high substrate input of up to 200 g/L in an organic solvent classified as “usable” according to the Pfizer Solvent Selection Guide, is presented. Graphical Abstract Efficient Enzymatic Amine Resolution at High Substrate Input Using Diethyl Malonate as an Acyl Donor of Low Hazard Potential