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The homogeneously catalyzed Guerbet upgrading of ethanol to butanol can be modulated by the application of partial H2 pressure before the reaction. Ruthenium(II) PNP pincer complexes with methylene‐extended acridine‐based ligands and singly‐chelated ruthenium(II) complexes with PN ligands perform best at very low catalyst loadings and upon the application of catalyst‐specific pre‐reaction partial H2 pressure. The combination of ruthenium(II) PNP pincer complexes and manganese(I) pincer complexes with MACHO‐type PNP ligands allows for even lower ruthenium loadings while retaining low base load and consumption, thus enabling high space‐time yields, catalyst productivity and recyclability. Mechanistically, Mn is proposed to stabilize coordinatively unsaturated Ru species and allow coordination of ethoxide to Ru instead of attacking the electrophilic ligand backbone based on NMR spectroscopy and X‐ray crystallography. [ABSTRACT FROM AUTHOR]

Polyurethanes are synthesized on industrial scale by the reaction of diisocyanates with diols in the presence of catalysts which are commonly based on tin complexes and amines. However, due to the toxicity and volatility of these tin catalysts and amines, there is the need to develop new catalysts that are more environmentally benign. Herein, we report the synthesis of O^N^O pincer‐ligated Mn(III) and Fe(III) complexes that serve as suitable catalysts for urethane formation and are stable to hydrolysis as predicted by computations and observed experimentally. The O^N^O pincer scaffold is vital to the activity of these catalysts, simultaneously ensuring increased solubility in the reaction medium as well as providing a stable framework upon dissociation of co‐ligands in the catalytic cycle. In silico mechanistic investigations for urethane formation show that the stabilization of active species in square‐planar geometries enabled by these O^N^O ligands permit the simultaneous coordination of alcohol and isocyanate in suitable configuration at the metal center. [ABSTRACT FROM AUTHOR]

An organocatalytic route has been developed for the isomerization of exo‐vinylene carbonates (exo‐VCs) to endo‐vinylene carbonates (endo‐VCs). The exo‐VC starting material can easily be obtained from propargylic alcohols via cyclization with carbon dioxide. In this study, these exo‐VCs are shown to isomerize to the thermodynamically more stable endo‐VCs in the presence of an N‐heterocyclic base and phenol. Density functional theory (DFT) studies were conducted to elucidate the mechanism, tackling difficulties of the description of charge separation steps. This isomerization process delivers an ample diversity of endo‐VCs in good to excellent yields and chemoselectivities under mild reaction conditions. [ABSTRACT FROM AUTHOR]

Herein, a general applicable method for the atom‐economic catalytic construction of a broad range of 1,2‐dialkylaminoethers is presented. By taking advantage of an elaborated protocol for the photocatalyzed anti‐Markovnikov selective hydroamination of nonactivated alkenes, a series of 1,2‐dialkylaminoethers was accessed by reacting readily available vinyl ethers with secondary alkyl amines. It was demonstrated that the reaction can be performed at low catalyst loadings while the commonly employed triisopropylbenzene thiol Hydrogen Atom Transfer (HAT)‐catalyst was replaced by an easier accessible mesityl thiol. Furthermore, the inexpensive and readily available diphenyl disulfide was proven as suitable HAT‐catalyst alternative for the efficient hydroamination of simple vinyl ethers. [ABSTRACT FROM AUTHOR]

Anilides are often found in pharmaceuticals and active ingredients in crop protection. Although of great interest, the atom‐ and step economic formation of the amide bond between a less nucleophilic aniline with an acid or ester remains still a major challenge. Herein, we report an aminolysis of aromatic and alkyl esters with anilines catalyzed by a readily available catalytic system comprising of an earth‐abundant Mn‐salt in combination with an inexpensive base. [ABSTRACT FROM AUTHOR]

(Co)poly-γ-butyrolactone (pGBL) is a thermoplastic material of high interest to replace common plastics with a more sustainable alternative due to its biodegradability, re-monomerizability and opportunity to be obtained from renewable feedstocks. Mild methods to produce pGBL by ring-opening polymerization (ROP) have only been developed in the last decade. Unfortunately, these methods involve the use of sophisticated catalysts, very low temperatures or relatively diluted mixtures. To develop a more environmentally, economically and industrially relevant pGBL synthesis process, the aim was to increase the ROP temperature to be applicable for large scale reaction and optimize the base/alcohol system to circumvent the use of sophisticated organic or rare earth metal catalysts. To that end, the strong base potassium tert-butoxide in combination with benzyl alcohol or with polyols such as 1,4-benzenedimethanol or glycerol was used for the ROP. This simple system gives access to high GBL conversions and medium to high molecular weight (co)polymers. [ABSTRACT FROM AUTHOR]

The influence of the ligand backbone on the enantioselectivity in the ruthenium‐catalyzed direct asymmetric reductive amination of acetophenone with NH3 and H2, using bidentate binaphthyl‐substituted phosphine ligands, was investigated in a combined computational and experimental study. A model for the bite angle dependence of the enantiomeric excess (ee) when using diphosphines bearing binaphthyl‐groups on the P‐atoms was developed. This revealed a significant potential for increasing the enantioselectivity, if ligands with a larger bite angle than the previously reported (S,S)‐f‐binaphane are used. Suitable backbone candidates were selected from more than one million structures provided by the Cambridge Structural Database (CCDC‐CSD) and the most promising candidates were synthesized accordingly. Despite all efforts, an increase of the ee was not possible with this approach. The larger backbones resulted in the preference of different ligand coordination modes avoiding the formation of the more strongly enantiodiscriminant substrate pocket between the naphthyl wings. [ABSTRACT FROM AUTHOR]

The Friedel‐Crafts sulfonylation for the synthesis of diaryl sulfones derivatives was achieved by using triflic acid (TfOH) as the acidic catalyst with aryl sulfonyl chlorides and arenes at elevated temperatures. Different sulfones could be synthesized with this method in good to excellent yield and with high selectivity. In contrast to the previous methodology reported for this sulfonylation, the catalyst and the excess of arene could be easily recovered and re‐used in further batches. [ABSTRACT FROM AUTHOR]

A copper(I)/phosphine system that homogeneously catalyses the alkynylation of formaldehyde with acetylene or terminal alkynes is reported. Using acetylene at atmospheric pressure, the catalyst consisting of <1 mol% copper(I) phenylacetylide and a trialkyl bisphosphine ligand shows a high selectivity towards the formation of propargyl alcohol rather than 1,4‐butynediol, which is not reported for common heterogeneous copper acetylide catalysts. The biphasic water/toluene reaction mixture allows the separation of targeted products with the aqueous layer and catalyst recycling via the organic layer. [ABSTRACT FROM AUTHOR]

Chemical recycling, in particular hydrogenative depolymerization, offers a promising way to utilize plastic waste. This report covers the manganese‐catalyzed hydrogenation of polyurethane materials to the corresponding monomeric units. The key to success is a Mn pincer complex as a potent hydrogenation catalyst in combination with elevated temperatures (up to 200 °C) and appropriate solvents to ensure sufficient solubility of the polymers. A wide range of polyurethane samples of varying polyol and isocyanate compositions, some of which feature significant amounts of urea functionalities, are depolymerized, releasing polyetherols and diaminotoluene (TDA) in yields of up to 89 % and 76 %, respectively. [ABSTRACT FROM AUTHOR]

The hydrogenation of (+)‐Sclareolide to (−)‐ambradiol catalyzed by a manganese pincer complex is reported. The hydrogenation reaction is performed with an air‐ and moisture‐stable manganese catalyst and proceeds under relatively mild reaction conditions at low manganese and base loadings. A range of other esters could be successfully hydrogenated leading to the corresponding alcohols in good to quantitative yields using this easy‐to‐make catalyst. A scale‐up experiment was performed leading to 99.3 % of the isolated yield of (−)‐Ambradiol. [ABSTRACT FROM AUTHOR]

In this paper, we present experimental results for a non-isothermal vertical confined backward facing step conducted with a low-Prandtl number fluid. The eutectic alloy gallium–indium–tin is used as the working fluid. We conducted experiments for different Reynolds and Richardson numbers covering both forced and mixed convection regimes. Time-averaged velocity profiles were measured at six streamwise positions along the test section center-plane with so-called permanent magnet probes. The local Nusselt number was measured in streamwise and spanwise directions along the heating plate mounted right after the step. We further ran RANS simulations of the experiment to study the qualitative influence of assuming a constant specific heat flux thermal boundary condition for the experiment heating plate. The measured velocity profiles show the expected behavior for both studied convection regimes, while the measured streamwise local Nusselt number profiles do not. This is explained by how the heating plate thermal boundary condition is defined. We performed an order of magnitude estimate to estimate the forced- to mixed convection transition onset. The estimate shows good agreement with the experimental data, although further measurements are needed to further validate the estimated transition threshold. The measurement of fluctuating quantities remains an open task to be addressed in future experiments, since the permanent magnet probe measurement equation needs further adjustments. [ABSTRACT FROM AUTHOR]

The Suzuki–Miyaura coupling reaction of electron-poor aryl chlorides in the synthesis of crop protection-relevant active ingredients in water is disclosed. Optimisation of the reaction conditions allowed running the reaction with 50 ppm of Pd-catalyst loading without an additional organic solvent in the cross-coupling reaction step in short reaction times. The system was optimised for the initial cross-coupling step of the large scale produced fungicides Boscalid, Fluxapyroxad and Bixafen up to 97% yield. It is also shown that the Suzuki–Miyaura reaction can be easily scaled up to 50 g using a simple product separation and purification using environmentally benign solvents in the work-up. To show the usability of this method, it was additionally applied in the three-step synthesis of the desired active ingredients. [ABSTRACT FROM AUTHOR]

Chemical recycling provides a promising solution to utilize plastic waste. Here, a catalytic hydrogenative depolymerization of polyamide 66 (PA 66) and polyurethane (PU) was developed. The system employed Ru pincer complexes at high temperature (200 °C) in THF solution, and even technical‐grade polymers could be hydrogenated with satisfactory yields under these conditions. A comparison of the system with some known heterogeneous catalysts as well as catalyst poisoning tests supported the homogeneity of the system. These results demonstrate the potential of chemical recycling to regain building blocks for polymers and will be interesting for the further development of polymer hydrogenation. [ABSTRACT FROM AUTHOR]

The simultaneous and local measurement of velocity and the temperature of a non-isothermal liquid metal flow has been an ongoing research topic over decades. The motivation is to obtain a detailed panorama of a liquid metal flow for the validation of turbulent heat flux models. So-called permanent magnet probes were used in the past for the local measurement of velocity and temperature profiles in liquid sodium in rather canonical flow configurations. The next step is to measure velocity and temperature profiles in a more complex flow geometry, namely a vertical confined backward facing step. For this, the permanent magnet probe must be adapted regarding its design, calibration procedure and temperature correction method. Particularly, considering that for this experiment the eutectic alloy of gallium, indium and tin was used as a working fluid, instead of liquid sodium, as in the mentioned past experiments. The main design aspects for a permanent magnet probe found in the literature are summarized and applied to the present probe. A calibration strategy for the probe was developed and implemented for the measurement of mean velocity profiles. A wetting procedure for the probe is proposed. The measured probe sensitivity for all six used probes agrees well with the theoretical estimations. The highest uncertainty contribution to measured sensitivity is related to the typical wetting issues of gallium–indium–tin. Future implementation of permanent magnet probes in general gallium–indium–tin experiments can make use of the developed know-how shared in this work. [ABSTRACT FROM AUTHOR]

Keywords: green chemistry; industrial chemistry; organic synthesis; synthetic methods EN green chemistry industrial chemistry organic synthesis synthetic methods 1865 1869 5 01/29/21 20210126 NES 210126 B Making industry greener b : Many principles for the economic production of organic bulk chemicals, the syntheses of which have potentially the highest environmental impact, currently overlap with principles of green chemistry. For about 93 % of the 250 million tons organic chemicals produced annually by oxidation, oxygen is used as the oxidant, in most cases in combination with catalysts to achieve appropriate selectivities.[3] I Addressed Principles of Green Chemistry: Prevent Waste, Atom Economy, Reduce Derivatives, Catalysis vs. Getting Greener: Propylene Oxide O SB 2 sb is not always the most efficient oxidant, as shown in the different synthetic routes to valuable propylene oxide (Scheme 4).[5] The chlorohydrin process uses chlorine and produces CaCl SB 2 sb as the by-product and is therefore not that green. This would allow the entry into a circular economy.[18, 19] Certain initiatives involving large chemical producers were recently started to introduce a circular economy based on chemcycling in order to replace the current linear use of feedstocks.[20] Greener alternatives should also be as economic as possible. [Extracted from the article]

We report a N-heterocyclic carbene copper(I) complex-catalysed formal cycloaddition between readily available propargylic alcohols and carbon dioxide at room temperature. By using the combination of a sterically demanding BPDPrCuCl complex (BPDPr = 1,3-bis(2,6-diisopropylphenyl)-1,3-diazonine-2-ylidene) and CsF, as catalytic system, primary propargylic alcohols are efficiently converted to the corresponding α-alkylidene cyclic carbonates. Gram scale (up to 89% yield) and reusability experiments (74% global yield, turnover number value = 103) showcase the robustness of the catalytic system. This practically simple protocol also tolerates secondary and tertiary propargylic alcohols under CO2 at atmospheric pressure, enabling the direct synthesis of substituted and unsubstituted α-alkylidene cyclic carbonates at room temperature. [ABSTRACT FROM AUTHOR]

A straight‐forward approach to separate catalyst from the exo‐vinylene carbonate (EVC) products of the carboxylative cyclisation of primary propargylic alcohols has been developed. The liquid‐liquid phase synthesis utilises lipophilic silver(I) carboxylate salts and N,N‐dioctyl modified phosphine (FatPhos) ligands to enhance catalyst solubility in non‐polar solvents. Following simple liquid‐liquid phase separation, EVCs relevant as monomers for poly(urethane) and poly(carbonate) synthesis were isolated in the non‐miscible polar phase in good yields. In situ reaction monitoring by ReactIR gave insights into the reaction kinetics and informed the conditions used to afford good EVC selectivity. Under optimised conditions, silver leaching into the product phase was very minor as confirmed by ICP‐MS. Furthermore, a protocol for catalyst recycling by liquid‐liquid separation was demonstrated, with modest loss of catalytic activity over 3 runs. [ABSTRACT FROM AUTHOR]

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Sugar alcohols are of great importance for the food industry and are promising building blocks for bio‐based polymers. Industrially, they are produced by heterogeneous hydrogenation of sugars with H2, usually with none to low stereoselectivities. Now, we present a homogeneous system based on commercially available components, which not only increases the overall yield, but also allows a wide range of unprotected ketoses to be diastereoselectively hydrogenated. Furthermore, the system is reliable on a multi‐gram scale allowing sugar alcohols to be isolated in large quantities at high atom economy. [ABSTRACT FROM AUTHOR]

The direct access to dimethoxymethane (DMM) from CO2/H2 in MeOH is an attractive approach, but more active, selective, and robust catalyst systems are still desirable for an application of this system. Herein, we present the performance enhancing effect of additives on ruthenium-triphos catalyst systems for CO2 hydrogenation to DMM. In the presence of PPh3, functioning as both additional ligand and precursor for Lewis-acidic phosphonium salts, increased turnover numbers for DMM are achieved. Moreover, PPh3 significantly diminishes catalyst degradation via carbonylation to cationic [RuH(CO)2(triphos)]OTf, which remains an active species in the synthesis of DMM. Catalyst recycling over up to five runs with minimal loss in catalyst performance underlines the robustness of the system. Both, the recyclability of the system and the suppression of catalyst deactivation pathways encourage for application in sustainable continuous processes. [ABSTRACT FROM AUTHOR]

Investigations concerning the reactivity of Ni(0) complexes [Ni(NHC)2] of NHCs (N‐heterocyclic carbene) of different steric demand, Mes2Im (= 1,3‐dimesitylimidazoline‐2‐ylidene) and iPr2Im (= 1,3‐diisopropyl‐imidazoline‐2‐ylidene), with olefins, ketones and aldehydes are reported. The reaction of [Ni(Mes2Im)2] 1 with ethylene or methyl acrylate afforded the complexes [Ni(Mes2Im)2(η2‐C2H4)] 3 and [Ni(Mes2Im)2(η2‐(C,C)‐H2C=CHCOOMe)] 4, as it was previously reported for [Ni2(iPr2Im)4(µ‐(η2:η2)‐COD)] 2 as a source for [Ni(iPr2Im)2]. In contrast to 2, complex 1 does not react with sterically more demanding olefins such as tetramethylethylene, 1,1‐diphenylethylene and cyclohexene. The reaction of [Ni(NHC)2] with more π‐acidic ketones or aldehydes led to formation of complexes with side‐on η2‐(C,O)‐coordinating ligands: [Ni(iPr2Im)2(η2‐O=CHtBu)] 5, [Ni(iPr2Im)2(η2‐O=CHPh)] 6, [Ni(iPr2Im)2(η2‐O=CMePh)] 7, [Ni(iPr2Im)2(η2‐O=CPh2)] 8, [Ni(iPr2Im)2(η2‐O=C(4‐F‐C6H4)2)] 9, [Ni(iPr2Im)2(η2‐O=C(OMe)(CF3))] 10 and [Ni(Mes2Im)2(η2‐O=CHPh)] 11, [Ni(Mes2Im)2(η2‐O=CH(CH(CH3)2))] 12, [Ni(Mes2Im)2(η2‐O=CH(4‐NMe2‐C6H4))] 13, [Ni(Mes2Im)2(η2‐O=CH(4‐OMe‐C6H4))] 14, [Ni(Mes2Im)2(η2‐O=CPh2)] 15 and [Ni(Mes2Im)2(η2‐O=C(4‐F‐C6H4)2)] 16. The reaction of 1 and 2 with these simple aldehydes and ketones does not lead to a significantly different outcome, but NHC ligand rotation is hindered for the Mes2Im complexes 3, 4 and 11–16 according to NMR spectroscopy. The solid‐state structures of 3, 4, 11 and 12 reveal significantly larger CNHC‐Ni‐CNHC angles in the Mes2Im complexes compared to the iPr2Im complexes. As electron transfer in d8‐ (or d10‐) ML2 complexes to π‐acidic ligands depends on the L–M–L bite angle, the different NHCs lead thus to a different degree of electron transfer and activation of the olefin, aldehyde or ketone ligand, i.e., [Ni(iPr2Im)2] is the better donor to these π‐acidic ligands. Furthermore, we identified two different side products from the reaction of 1 with benzaldehyde, trans‐[Ni(Mes2Im)2H(OOCPh)] 17 and [Ni2(Mes2Im)2(µ2‐CO)(µ2‐η2‐C,O‐PhCOCOPh)] 18, which indicate that radical intermediates and electron transfer processes might be of importance in the reaction of 1 with aldehydes and ketones. [ABSTRACT FROM AUTHOR]

The direct conversion of ketones into chiral primary amines is a key transformation in chemistry. Here, we present a ruthenium catalyzed asymmetric reductive amination (ARA) of purely aliphatic ketones with good yields and moderate enantioselectivity: up to 99 % yield and 74 % ee. The strategy involves [Ru(PPh3)3H(CO)Cl] in combination with the ligand (S,S)‐f‐binaphane as the catalyst, NH4I as the amine source and H2 as the reductant. This is a straightforward and user‐friendly process to access industrially relevant chiral aliphatic primary amines. Although the enantioselectivity with this approach is only moderate, to the extent of our knowledge, the maximum ee of 74 % achieved with this system is the highest reported till now apart from enzyme catalysis for the direct transformation of ketones into chiral aliphatic primary amines. [ABSTRACT FROM AUTHOR]

The reaction of cyclic amides with acetylene under low pressure, using ruthenium-phosphine catalysts, afforded a broad variety of N-vinylated amides including (azabicyclic) lactams, oxazolidinones, benzoisoxazolones, isoindolinones, quinoxalinones, oxazinanones, cyclic urea derivatives (imidazolidinones), nucleobases (thymine), amino acid anhydrides and thiazolidinone. [ABSTRACT FROM AUTHOR]

Using the bulk chemical 1,4-butynediol, readily available epoxides and carbon dioxide, a new series of unsubstituted exovinylene carbonates were synthesised. Chemoselective additions of diamines or diols to these cyclic carbonates allow the regiocontrolled synthesis of new functionalised polyurethanes and polycarbonates under mild conditions. This route to polyurethanes avoids the use of toxic isocyanates. [ABSTRACT FROM AUTHOR]

A new approach for the efficient and highly selective synthesis of 1,2‐amino alcohols by direct reductive hydrolysis of N‐formyl‐protected α‐amino nitriles is reported. The commercially available RuHCl(CO)(PPh3)3 complex was found to be a suitable catalyst for this operationally simple protocol, in which no stoichiometric amounts of undesired metal waste are generated. The deaminative hydrogenation is performed at 55 bar of H2, using a 6:1 mixture of 1,4‐dioxane/water as solvent. In addition, hydroxymethyl alcohols were prepared from cyanoketones under very similar conditions. [ABSTRACT FROM AUTHOR]

Direct α‐Trifluoromethylation of acetophenone derivatives was achieved by using trifluoroacetic anhydride (TFAA) as the trifluoromethyl source and pyridine‐N‐oxide (Py−O) as activator and oxidant under visible light irradiation and tris‐(2,2′‐bipyridine)ruthenium(II) hexafluorophosphate (Ru(bpy)3(PF6)2) as the photocatalyst. Different acetophenone derivatives could be converted to the corresponding α‐CF3 derivatives with high selectivity. Extensive mechanistic investigation revealed the formation of vinyl trifluoroacetate as the key intermediate for this transformation. [ABSTRACT FROM AUTHOR]

The use of carbon dioxide (CO2) as a building block in organic synthesis is a topic of high interest. We here reflect from an industrial perspective, which of the approaches may have the potential to be applied in the near future in industrial organic synthesis on a significant scale. Drawbacks to overcome and challenges to be addressed are also discussed in this critical review. This review focuses on systems providing a high atom‐efficiency and which could be competitive to other state‐of‐the art syntheses. [ABSTRACT FROM AUTHOR]

Sodium acrylate is a valuable monomer for the synthesis of superabsorbents and produced industrially on large scale. Currently, sodium acrylate is made by the oxidation of propene to acrylic acid followed by neutralization with NaOH. The synthesis of sodium acrylate from CO2, ethylene, and NaOH would be very attractive due to lower raw material costs but was for many years only a "dream reaction." Significant progress has been made since the first report in 2012 on a catalytic system for this synthesis. Different nickel and palladium catalysts were identified. In addition, the influence of the base in this reaction was evaluated. The use of solvents fulfilling certain criteria is necessary for the design of continuous process concepts. To date, two process concepts have resulted: one using phenolate bases and the other utilizing alkoxide bases. [ABSTRACT FROM AUTHOR]

In this report, hydroxymethylfurfural (HMF) is used as a bio-based feedstock for homogeneous metal-catalysed hydrogenation. Several ligand classes and metals are employed to reduce the aldehyde and aromatic ring of HMF. The previously unknown homogeneous catalysed hydrogenation of HMF to tetrahydrofuran-dimethanol (THFDM) was investigated using different catalyst systems. NHCs and phosphites give higher trans/cis ratios (between 1 : 1.25 and 1 : 3.95) of the product THFDM, but low conversions of only up to 17% accompanied by up to 92% yield of bis(hydroxymethyl)furan at 10 bar H2 and 120 °C. Conversely, di-phosphine ligated ruthenium catalysts in up to 87% yield lead to the highest overall conversion but only moderate trans/cis ratios of only 1 : 3.1–1 : 5. [ABSTRACT FROM AUTHOR]

Abstract: In this study, known homogeneous and heterogeneous chromium(VI) catalyst systems were investigated with respect to the favored formation of cyclohexanone during the decomposition of cyclohexyl hydroperoxide (CHHP). The focus was on mechanistic studies using different spectroscopic methods as well as DFT calculations to further optimize the reaction conditions. As in previous decomposition studies, a mechanism via the formation of a metal alkylperoxido intermediate is probable. In situ spectroscopic studies revealed that in case of both the soluble and insoluble catalyst, the selective decomposition happens via a non‐radical, non‐redox mechanism at the CrVI stage through the formation of a cyclohexylperoxychromium(VI) complex. The proposed mechanism is supported by thorough DFT calculations. [ABSTRACT FROM AUTHOR]

The deaminative hydrogenation of nitriles towards alcohols is a useful reaction to transform nitriles into alcohols with NH3 as the sole byproduct. Using the simple and robust RuHCl(CO)(PPh3)3 complex as a catalyst, at low H2 pressures a series of aliphatic and aromatic nitriles could be transformed into the corresponding alcohols. Suitable solvent systems for these reactions were 1,4-dioxane/water and EtOH/water mixtures. In most cases, the selectivity for the alcohols was excellent, and the corresponding amines were formed only in trace amounts. [ABSTRACT FROM AUTHOR]

A cooperative methoxy transfer between orthosilicate esters and organotin oxides was developed for the synthesis of various N-alkyl and N-aryl carbamates from carbon dioxide in up to 97% isolated yield. The reaction is highly selective and N-alkylated amines are not observed. Density functional theory calculations of the reaction were performed and, together with NMR observations, a plausible mechanism featuring the catalytic regeneration of dialkyltin dialkoxide is proposed. [ABSTRACT FROM AUTHOR]

The Pd-catalysed synthesis of sodium acrylate from ethylene and CO2 in the presence of alcoholate bases has been improved significantly. We used amide solvents such as N-cyclohexylpyrrolidone or N, N-dibutylformamide to achieve turnover numbers greater than 500 in one run, which is significantly higher than that of systems for this reaction reported previously. For the first time, we were able to recycle the catalyst without any additional regeneration step. With this system, it is possible to use the simple and easily recycled alcoholate base sodium isopropoxide to achieve good turnover numbers up to 200. [ABSTRACT FROM AUTHOR]

A straightforward phosgene-free synthesis of aromatic isocyanates and diisocyanates is disclosed. Theoretical investigations suggested that the insertion of carbon dioxide (CO2) by dialkyltin(IV) dialkoxides could be used to convert aromatic amines into aromatic mono- and dicarbamates. Here we show, that methyl phenylcarbamate (MPC) from aniline using organotin(IV) dimethoxide and CO2 can be formed in high yield of up to 92 %, experimentally corroborating the predictions of density functional theory (DFT) calculations. MPC was then separated from the tin oxide residues and converted into phenyl isocyanate. Furthermore, organotin(IV) alkoxides could be regenerated from the tin oxide residues and reused, paving the way for a continuous industrial process. Extension of the scope to the synthesis of diurethanes from toluene 2,4-diamine and 4,4′-methylenedianiline could potentially allow the efficient production of industrially relevant diisocyanates. [ABSTRACT FROM AUTHOR]

A highly selective reductive amination of ketones to primary amines with ammonia and hydrogen using a simple ruthenium catalyst has been developed. The protocol described constitutes an efficient and direct atom-economical approach en route to α-methylbenzylamine derivatives in good to high yields. The presence of catalytic amounts of aluminum triflate turned out to be crucial for achieving high conversion towards primary amines. [ABSTRACT FROM AUTHOR]

The synthesis of sodium acrylate through catalytic carboxylation of ethylene with CO2 in the presence of a base is a reaction of high interest. To develop a more efficient and sustainable method to access this valuable acrylate monomer, we optimized the system in a one-step homogeneous nickel- or palladium-catalyzed reaction, without the need for stoichiometric amounts of an additional reducing agent. Suitable nontoxic solvents such as anisole instead of the previously reported tetrahydrofuran or chlorobenzene were found to lead to acrylate formation. In combination with appropriate phenolate bases, this could allow a rational process concept for a simple catalyst recycling, product separation, and base regeneration. [ABSTRACT FROM AUTHOR]

The carboxylation of olefins beyond ethylene towards α,β-unsaturated carboxylic acid salts and a detailed investigation on the critical steps in the catalysis are reported. The influence of two chelating phosphine ligands and several olefins on the elemental steps of the catalysis is shown. The work focusses on the formation of intermediate olefin complexes, lactone formation and base induced elimination of the lactone. The direct carboxylation of olefins is possible using nickel catalysts, which opens a new route towards the desired α,β-unsaturated carboxylic acid salts. The reaction works particularly well for 1,3-dienes and proceeds via the formation of allyl-carboxylates. The ability to form such allyl-type lactone complexes seems in this case to be the most challenging step towards satisfactory turnover numbers. [ABSTRACT FROM AUTHOR]

The unique reactivity of the nickel(0) complex [Ni2(iPr2Im)4(COD)] (1) (iPr2Im = 1,3-di-isopropyl-imidazolin-2-ylidene) towards hydrosilanes in stoichiometric and catalytic reactions is reported. A series of nickel hydrido silyl complexes cis-[Ni(iPr2Im)2(H)(SiHn-1R4-n)] (n = 1, 2) and nickel bis(silyl) complexes cis-[Ni-(iPr2Im)2(SiHn-1R4-n)2] (n = 1, 2, 3) were synthesized by stoichiometric reactions of 1 with hydrosilanes HnSiR4-n, and fully characterized by X-ray diffraction and spectroscopic methods. These hydrido silyl complexes are examples where the full oxidative addition step is hindered. They have, as a result of the remaining Si-H interactions, remarkably short Si-H distances and feature a unique dynamic behavior in solution. Cis-[Ni(iPr2Im)2(H)(SiMePh2)] (cis-5) shows in solution at room temperature a dynamic site exchange of the NHC ligands, H-D exchangewith C6D6 to give the deuteride complex cis-[Ni(iPr2Im)2(D)-(SiMePh2)] (cis-5-D), and at elevated temperatures an irreversible isomerization to trans-[Ni(iPr2Im)2(D)-(SiMePh2)] (trans-5-D). Reactions with sterically less demanding silanes give cis-configured bis(silyl) complexes accompanied by the release of dihydrogen. These complexes display, similarly to the hydrido silyl complexes, interestingly short Si-Si distances. Complex 1 reacts with 4 eq. HSi(OEt)3, in contrast to all the other silanes used in this study, to give the trans-configured bis(silyl) complex trans-[Ni(iPr2Im)2Ni-(Si(OEt)3)2] (trans-12). The addition of two equivalents of Ph2SiH2 to 1 results, at elevated temperatures, in the formation of the dinuclear complex [{(iPr2Im)Ni-µ²-(HSiPh2)}2] (6). This diamagnetic, formal Ni(I) complex exhibits a long Ni-Ni bond in the solid state, as established by X-ray diffraction. The capability of the electron rich {Ni(iPr2Im)2} complex fragment to activate Si-H bonds was applied catalytically in the deuteration of Et3Si-H to Et3Si-D employing C6D6 as a convenient deuterium source. Furthermore, we show that 1 serves as a catalyst for the acceptorless dehydrogenative coupling of Ph2SiH2 to the corresponding disilane Ph2HSi-SiHPh2 and trisilane Ph2HSi-Si(Ph)2-SiHPh2, and the coupling of PhSiH3 to give a mixture of cyclic and linear polysilanes with high polydispersity (Mw = 1119; Mn = 924; Mw/Mn = 1.2). The capability of 1 to catalyze the formal reverse reaction as well is demonstrated by the hydrogenation of disilanes. The hydrogenation of the disilanes Ph2MeSi-SiMePh2 and PhMe2Si-SiMe2Ph to the corresponding hydrosilanes Ph2MeSi-H and PhMe2Si-H, respectively, proceeds effectively in the presence of 1 under very mild conditions (room temperature, 1.8 bar H2 pressure). [ABSTRACT FROM AUTHOR]

Focuses on the worldwide prevalence of peritoneal dialysis. Judgment of treatment modality; Improvement of technique and patient survival; Residual renal function.

Presents an interview with author Stephen Wright discussing his writing technique. Comments on the book `Meditations in Green'; Information on the book `Going Native'; What Wright aims for in his writing.

Features an interview with American writer Marilynne Robinson held in Wisconsin, Madison on April 1993. Discussion of her book `Housekeeping;' Representation of the importance of women in the West; Robinson's concept of the ideal book; Experience as transcending the idiomatic vernacular; Logic of a book as an emotional logic; Modern understanding of the world.

Presents a provocative response to the article 'The Crying of Lot 49' by Edward Mendelson published in the journal 'Boundary 2.' Theme of the article; Literary style of Mendelson in the article.

Plain X-rays computed tomographic and magnetic resonance images all yield information on the pathophysiology of diseases with spinal involvement. Descriptions of the following nuclear medicine methods are presented: The value of the various nuclear medicine methods in the diagnostic schedule is illustrated in case reports. [ABSTRACT FROM AUTHOR]