Reduction of sulfoxides with boranes catalyzed by MoO2Cl2

The first example of an organic reduction with boranes catalyzed by a high valent oxo-complex is reported. The systems catecholborane/MoO₂Cl₂(H₂O)₂ (5 mol %) and BH₃·THF/MoO₂Cl₂ (5 mol %) proved to be very efficient for the reduction of sulfoxides to the corresponding sulfides in excellent yields.     

How to Control the Chemoselectivity of the Catalytic Formation of Chiral γ-Lactams or 2,3-Disubstituted Pyrroles by the Choice of Solvent

Summary. The reaction of the unsaturated imine methyl(3-phenylallylidene)amine with ethylene and carbon monoxide in the presence of catalytical amounts of Ru₃(CO)₁₂ leads to the formation of two heterocyclic products. One of the products is a chiral γ-lactam, the other one a 2,3-disubstituted pyrrole derivative, in which only the carbon atom from carbon monoxide is incorporated. The selectivity in the formation of the products may be controlled by the choice of solvent. In general, in nonpolar solvents the formation of the lactam is preferred whereas the use of more polar solvents enhances the yield of the pyrrole. For most of the solvents used there is a linear dependence of the product ratio on the relative permittivity of the corresponding solvent. Typically, polar aprotic solvents do not follow this rule.     

Nonisothermal Kinetics of Sub‐Solidus Phase Transitions in C10Zn,C16Zn and Their Binary System

Nonisothermal kinetics of the solid‐solid phase transition in (n‐C₁₀H₂₁NH₃)₂ZnCl₄(C₁₀Zn), (n‐C₁₆H₃₃NH₃)₂ZnCl₄(C₁₆Zn) and their binary system were determined by Kissinger and Ozawa methods from DSC measurements. The activation energy E_a of the binary system shows a waving dependence on W_C10Zn%, which is caused by not only an intermediate (C₁₀H₂₁NH₃)(n‐C₁₆H₃₃NH₃)ZnCl₄ but also three solid solution ranges (α, β, γ) in the phase diagram of C₁₀Zn‐C₁₆Zn. The variations of the layer d‐spacing are also convenient for the above result.     

纳米多孔二氧化钛电极辅助光电化学降解乙酰氨基酚及伐昔洛韦

作为一类具有较高生物活性的物质,药物及个人护理品对环境的污染引起人们越来越多的关注.对乙酰氨基酚和伐昔洛韦是两种使用广泛的药物,由于其潜在的对人类健康和生态安全的威胁而逐渐成为研究热点.而电化学辅助光氧化技术因其具备能够高效处理难降解化学品的优点而得到广泛使用.本文合成了纳米多孔二氧化钛电极,研究了电化学还原处理对纳米多孔二氧化钛电极辅助光电化学降解对乙酰氨基酚和伐昔洛韦的影响.使用扫描电镜和色散谱技术对合成的纳米多孔二氧化钛电极的形态和元素组成进行了表征.循环伏安法、莫特-肖特基曲线、紫外-可见分光光度计和总有机碳分析仪被用来研究对乙酰氨基酚和伐昔洛韦的光电化学降解过程.结果显示,对乙酰氨基酚和伐昔洛韦的光化学降解和电化学降解过程非常缓慢,在研究的时间范围内其浓度未见明显变化,因此可以忽略不计.但是对乙酰氨基酚和伐昔洛韦的光电化学降解速度比较快,与未经处理的纳米多孔二氧化钛电极相比,经过电化学还原处理的电极可以使对乙酰氨基酚和伐昔洛韦的光电化学降解分别提高86.96%和53.12%.这可能是由于在电化学还原处理过程中生成了Ti3+, Ti2+和氧空位以及导电性的提高.还研究了温度对对乙酰氨基酚和伐昔洛韦光电化学降解的影响,随着温度升高,对乙酰氨基酚和伐昔洛韦的光电化学降解速率增大.     

丙三醇浓溶液玻璃化转变与结构松弛参数DSC分析

In order to examine the effects of water contents and heating/cooling rates on the glass transition and the structure relaxation parameters of glycerol/water mixtures, five aqueous solutions (60%, 70%, 80%, 90% and 100%) were investigated using the differential scanning calorimetry. Four scanning rates (10, 15, 20, 25 K/min) were used to obtain the glass transition parameters. The fitting results of plasticization constants indicated that Gordon-Taylor relationship could not be used effectively without considering scanning rates and that point on calorimetric step was chosen as the glass transition temperature. The specific heat changes during glass transition processes were relative not only to water content but also to heating rates. With the increasing of water contents in glycerol aqueous solutions, the structure relaxation activation energies and dynamic fragilities were decreased. Since the thermodynamic fragilities were increased with the increasing of water content, so the dynamic fragility and thermodynamic fragility were changed inversely if the water contents were changed in glycerol/water mixtures.     

Physicochemical Characteristics of Polypyrrole/(Glucose oxidase)/(Prussian Blue)‐based Biosensor Modified with Ni‐ and Co‐Hexacyanoferrates

In this work, three types of electrodes suitable for amperometric glucose biosensors were designed. One type of electrode was based on bio‐selective layer of polypyrrole/(glucose oxidase)/(Prussian Blue) (Ppy/GOx/PB) and it was used as a control electrode regarding to which electrochemical properties of two other types of electrodes were compared. During the formation of Prussian blue layers graphite electrodes were additionally modified by Ni‐hexacyanoferrate (NiHCF) and by Co‐hexacyanoferrate (CoHCF) in order to design Ppy/GOx/PB‐NiHCF and Ppy/GOx/PB‐CoHCF electrodes, respectively. Some physicochemical characteristics of all three types of electrodes were evaluated and compared. The Ppy/GOx/PB‐NiHCF electrode showed wider linear range of the calibration curve than Ppy/GOx/PB and Ppy/GOx/PB‐CoHCF electrodes. The effect of temperature on analytical performance of the Ppy/GOx/PB‐NiHCF based biosensor has been evaluated and activation energy of enzyme catalysed reaction has been calculated within the temperature range of 15 °C to 30 °C.     

New Ga/N‐based Active Lewis Pairs,Trifunctional Ga–Ga Compounds,Reactions with Cyanamide and Dual Insertion of Isocyanate

Hydrogallation of Me₃Si–C≡C–NR'₂ with R₂Ga–H (R = tBu, CH₂tBu, iBu) yielded Ga/N‐based active Lewis pairs, R₂Ga–C(SiMe₃)=C(H)–NR'₂ ( 7 ). The Ga and N atoms adopt cis‐positions at the C=C bonds and show weak Ga–N interactions. tBu₂GaH and Me₃Si–C≡C–N(C₂H₄)₂NMe afforded under exposure of daylight the trifunctional digallium(II) compound [MeN(C₂H₄)₂N](H)C=C(SiMe₃)Ga(tBu)–Ga(tBu)C(SiMe₃)=C(H)[N(C₂H₄)₂NMe] ( 8 ), which results from elimination of isobutene and H₂ and Ga–Ga bond formation. 8 was selectively obtained from the ynamine and [tBu(H)Ga–Ga(H)tBu]₂[HGatBu₂]₂. 7a (R = tBu; NR'₂ = 2,6‐Me₂NC₅H₈) and H₈C₄N–C≡N afforded the adduct tBu₂Ga‐C(SiMe₃)=C(H)(2,6‐Me₂NC₅H₈) · N≡C–NC₄H₈ ( 11 ) with the nitrile bound to gallium. The analogous ALP with harder Al atoms yielded an adduct of the nitrile dimer or oligomers of the nitrile at room temperature. The reaction of 7a with Ph–N=C=O led to the insertion of two NCO groups into the Ga–C_vinyl bond to yield a GaOCNCN heterocycle with Ga bound to O and N atoms ( 12 ).     

Conformationally Flexible Biphenyl‐phosphane Ligands for Ru‐Catalyzed Enantioselective Hydrogenation

Stereomutation of a BIPHEP/RuCl ₂ /diamine complex (shown schematically) is possible because of the conformational flexibilty of BIPHEP ligands. The result is an asymmetric activation in the Ru‐catalyzed hydrogenation of carbonyl compounds to optically active alcohols. Whereas a racemic BINAP/RuCl₂ complex with a chiral diamine activator gives a 1:1 mixture of two diastereomers, unequal amounts of the diastereomers can be produced from a BIPHEP/RuCl₂ complex and a chiral diamine. Ar=3,5‐dimethylphenyl, BINAP=2,2′‐bis(diphenylphosphanyl)‐1,1′‐binaphthyl, BIPHEP=2,2′‐bis(diarylphosphanyl)biphenyl.     

O2+O2 electron transfer reactivity in the quartet state from ab initio calculation including electron correlation

The structures and properties of the O₂+O₂⁻ electron transfer system in the quartet state, both in the gaseous phase and in solution, were studied at the UMP2(full)/6-311+G* basis set level for the five selected coupling structures: two T-type, collinear, parallel, and crossing. The stabilities of these encounter complexes were compared. The activation barriers, coupling matrix elements, and the electron transfer rate at two theoretical levels (semiclassical and quantum mechanical) were also calculated for the quartet state, and the effect of the solvent medium evaluated at the self-consistent reaction field level. Results indicate that the structures and properties of the encounter complexes directly affect the mechanism and rate of the electron transfer reaction, the contact distances for this O₂…O₂⁻ were generally large (3 Å), the interaction between the donor and the acceptor was weak, and the structures are floppy. The electronic transmission factor for the reacting system, O₂+O₂⁻, was less than unity (ca. 001–0.6), thus the electron transfer reaction was non-adiabatic in nature. Analysis of the dependence of relevant kinetic parameters on various influencing factors showed that the effect of the solvent medium on the coupling matrix element was small, but that on the electron transfer rate was very large, and the gaseous phase results for the molecular geometrical parameters and their contributions can directly transfer to solution. Among the five selected transition state structures, the electron transfer was more likely to take place via the T-type and the P-type structures, the rate values from two theoretical levels were in good agreement with each other and were also very close to the experimental findings. If the various anharmonic vibrational contributions, the effect of the solvent molecular electronic structures and the interaction between the reacting species and the solvent medium are taken into account, the results can be improved.     

Theoretical insights into the mechanism of photocatalytic reduction of CO2 over semiconductor catalysts

Photocatalytic reduction of CO₂ is one important approach to alleviate greenhouse gas emission and energy crisis, which has gained huge attention in the past decades. However, the lack of understanding complex reaction mechanism impedes new catalysts design. It is also very difficult to understand the mechanism by using only experimental approaches. For this concern, theoretical calculations can effectively supplement the experimental deficiency and thus play an important role. Recently theoretical calculations have been performed on adsorption, migration and reduction of CO₂ molecule on the photocatalyst surface, leading to useful information that have contributed greatly to this field. This review summarizes recent advances in first-principles calculations about CO₂ photoreduction over various semiconductor photocatalysts like metal oxides, sulfides and g-C₃N₄. The methods, models, adsorption and reaction pathways have been discussed in detail. The perspective about future investigation on the photocatalytic reduction of CO₂ using first principles calculations is also presented.