Chemical Dynamic Kinetic Resolution and S/R Interconversion of Unprotected α‐Amino Acids

Reported herein is the first purely chemical method for the dynamic kinetic resolution (DKR) of unprotected racemic α‐amino acids (α‐AAs), a method which can rival the economic efficiency of the enzymatic reactions. The DKR reaction principle can be readily applied for S/R interconversions of α‐AAs, the methodological versatility of which is unmatched by biocatalytic approaches. The presented process features a virtually complete stereochemical outcome, fully recyclable source of chirality, and operationally simple and convenient reaction conditions, thus allowing its ready scalability. A quite unique and novel mode of the thermodynamic control over the stereochemical outcome, including an exciting interplay between axial, helical, and central elements of chirality is proposed.     

Hydrolytic Kinetic Resolution of Terminal Epoxides catalyzed by Novel Bimetallic Chiral Co (Salen) Complexes

Novel bimetallic chiral Co (salen) complexes bearing transition‐metal salts have been synthesized. The easily prepared complexes exhibited very high catalytic reactivity and enantioselectivity in hydrolytic kinetic resolution (HKR) of racemic terminal epoxides and consequently provided enantiomerically enriched epoxides (up to 99% ee).     

Metal-Organic Framework (MOF) Morphology Control by Design

Exerting morphological control over metal-organic frameworks (MOFs) is critical for determining their catalytic performance and to optimize their packing behavior in areas from separations to fuel gas storage. A mechanism-based approach to tailor the morphology of MOFs is introduced and experimentally demonstrated for five cubic Zn₄O-based MOFs. This methodology provides three key features: 1) computational screening for selection of appropriate additives to change crystal morphology based on knowledge of the crystal structure alone; 2) use of additive to metal cluster geometric relationships to achieve morphologies expressing desired crystallographic facets; 3) potential for suppression of interpenetration for certain phases.     

手性(salen)Co配合物的合成及其在水解动力学拆分中的应用

综述了近几年来手性(salen) Co金属配合物的合成及其在水解动力学拆分末端环氧化合物中的应用。设计更合适的配体、发展可重复利用的催化剂、对催化剂及催化体系进行理论和模拟是当前乃至今后该领域研究工作的重点。     

Structure,Luminescent Sensing and Proton Conduction of a Boiling-Water-Stable Zn(II) Metal-Organic Framework

A novel Zn(II) metal-organic framework [Zn₄O(C₃₀H₁₂F₄O₄S₈)₃]_n, namely ZnBPD-4F4TS, has been constructed from a fluoro- and thiophenethio-functionalized ligand 2,2′,5,5′-tetrafluoro-3,3′,6,6′-tetrakis(2-thiophenethio)-4,4′-biphenyl dicarboxylic acid (H₂BPD-4F4TS). ZnBPD-4F4TS shows a broad green emission around 520 nm in solid state luminescence, with a Commission International De L’Eclairage (CIE) coordinate at x = 0.264, y = 0.403. Since d¹⁰-configured Zn(II) is electrochemically inert, its photoluminescence is likely ascribed to ligand-based luminescence which originates from the well-conjugated system of phenyl and thiophenethio moieties. Its luminescent intensities diminish to different extents when exposed to various metal ions, indicating its potential as an optical sensor for detecting metal ion species. Furthermore, ZnBPD-4F4TS and its NH₄Br-loaded composite, NH₄Br@ZnBPD-4F4TS, were used for proton conduction measurements in different relative humidity (RH) levels and temperatures. Original ZnBPD-4F4TS shows a low proton conductivity of 9.47 × 10⁻¹⁰ S cm⁻¹ while NH₄Br@ZnBPD-4F4TS shows a more than 25,000-fold enhanced value of 2.38 × 10⁻⁵ S cm⁻¹ at 40 °C and 90% RH. Both of the proton transport processes in ZnBPD-4F4TS and NH₄Br@ZnBPD-4F4TS belong to the Grotthuss mechanism with E_a = 0.40 and 0.32 eV, respectively.     

A Versatile Co(bisalen) Unit for Homogeneous and Heterogeneous Cooperative Catalysis in the Hydrolytic Kinetic Resolution of Epoxides

Bisalen—very cooperative : A novel styryl‐substituted, unsymmetrical bisalen is shown to be a versatile precursor to both soluble and insoluble cooperative catalysts for the hydrolytic kinetic resolution of epoxides. The unique bisalen motif ensures all catalysts derived from it have the necessary molecular‐level ligand pairing needed for cooperative bimetallic catalytic reactions (see scheme).

     

Highly Enantioselective Kinetic Resolution of Axially Chiral BINAM Derivatives Catalyzed by a Brønsted Acid

A highly efficient strategy for the kinetic resolution of axially chiral BINAM derivatives involving a chiral Brønsted acid‐catalyzed imine formation and transfer hydrogenation cascade process was developed. The kinetic resolution provides a convenient route to chiral BINAM derivatives in high yields with excellent enantioselectivities.     

Molecular Mobility of Tert-butyl Alcohol Confined in a Breathing MIL-53 (Al) Metal-Organic Framework

We present a detailed solid-state NMR characterization of the molecular dynamics of tert-butyl alcohol (TBA) confined inside breathing metal-organic framework (MOF) MIL-53(Al). ²⁷Al MAS NMR has demonstrated that TBA adsorption induces the iX phase of MIL-53 material with partially shrunk channels. ²H solid-state NMR has shown that the adsorbed alcohol exhibits anisotropic rotations of the methyl groups around two axes and librations of the molecule as a whole about the axis passing through the TBA C−O bond. These librations are realized by two distinct ways: fast molecule orientation change during the translational jump diffusion along the channel with characteristic time τ_D of about 10⁻⁹ s at 300 K; slow local librations at a single coordination site, representing framework hydroxyl groups, with τ_l≈10⁻⁶ s at 300 K. Self-diffusion coefficient of the alcohol in the MOF has been estimated: D=3.4×10⁻¹⁰ m² s⁻¹ at 300 K. It has been inferred that both the framework flexibility and the interaction with framework hydroxyl groups define the dynamics of TBA confined in the channels of MIL-53 (Al).     

Dynamic Kinetic Resolution of Heterobiaryl Ketones by Zinc‐Catalyzed Asymmetric Hydrosilylation

A diastereo‐ and highly enantioselective dynamic kinetic resolution (DKR) of configurationally labile heterobiaryl ketones is described. The DKR proceeds by zinc‐catalyzed hydrosilylation of the carbonyl group, thus leading to secondary alcohols bearing axial and central chirality. The strategy relies on the labilization of the stereogenic axis that takes place thanks to a Lewis acid–base interaction between a nitrogen atom in the heterocycle and the ketone carbonyl group. The synthetic utility of the methodology is demonstrated through stereospecific transformations into either N,N‐ligands or appealing axially chiral, bifunctional thiourea organocatalysts.     

Recyclable Ligands for the Non‐Enzymatic Dynamic Kinetic Resolution of Challenging α‐Amino Acids

Structurally simple and inexpensive chiral tridentate ligands were employed for substantially advancing the purely chemical dynamic kinetic resolution (DKR) of unprotected racemic tailor‐made α‐amino acids (TM‐α‐AAs), enabling the first DKR of TM‐α‐AAs bearing tertiary alkyl chains as well as multiple unprotected functional groups. Owing to the operationally convenient conditions, virtually complete stereoselectivity, and full recyclability of the source of chirality, this method should find wide applications for the preparation of TM‐α‐AAs, especially on large scale.     

(S)‐Selective Kinetic Resolution and Chemoenzymatic Dynamic Kinetic Resolution of Secondary Alcohols

(S)‐Selective kinetic resolution was achieved through the use of a commercially available protease, which was activated with a combination of two different surfactants. The kinetic resolution (KR) process was optimized with respect to activation of the protease and to the acyl donor. The KR proved to be compatible with a range of functionalized sec‐alcohols, giving good to high enantiomeric ratio values (up to >200). The enzymatic resolution was combined with a ruthenium‐catalyzed racemization to give an (S)‐selective dynamic kinetic resolution (DKR) of sec‐alcohols. The DKR process works under very mild reaction conditions to give the corresponding esters in high yields and with excellent enantioselectivities.     

Synergistic Kinetic Resolution and Asymmetric Propargyl Claisen Rearrangement for the Synthesis of Chiral Allenes

The asymmetric propargyl Claisen rearrangement provides a convenient entry to chiral allene motifs. Herein, we describe the development of a kinetic resolution and asymmetric rearrangement of racemic propargyl vinyl ethers. This transformation afforded chiral allene products along with the enantiomerically enriched substrate in good yields with excellent diastereo‐ and enantioselectivity. The complete chirality transfer and facially selective rearrangement enabled the simultaneous construction of an axially chiral allenic unit and a quaternary carbon stereocenter.     

手性金属-有机骨架材料[Cu(S-mal)(bpy)]n用于高效液相色谱拆分外消旋化合物

手性金属-有机骨架材料作为一种新型的多孔材料,在手性分离领域备受关注.以S-苹果酸和4,4'-联吡啶为配体与醋酸铜反应,通过溶剂热法合成了一种具有三维手性网状结构的手性金属-有机骨架材料[Cu（S-mal）（bpy）]_n.将其用作固定相制成高效液相色谱手性柱,采用不同比例的正己烷/异丙醇作为流动相对一系列外消旋化合物进行手性拆分.结果显示,该手性柱对醇类、酮类、黄酮、酚类、胺类等17种外消旋化合物表现了较好的手性拆分能力.将该手性柱与之前我们报道的3种手性MOFs柱相比较,其表现出了更好的手性选择性,具有较好的手性拆分互补作用.最后还对该手性柱的重现性和稳定性做了评价,结果表明该手性柱表现出较好的重现性和稳定性.     

金属-有机框架材料在光催化二氧化碳还原中的应用

CO₂的过度排放导致全球环境问题日益严重,如何将CO₂有效地利用起来成为全世界的研究热点。相比于高耗能的CO₂捕获和储存(CCS)技术,通过催化反应将CO₂转化为有价值的能源燃料是同时解决能源危机和环境问题的有效途径。其中,使用太阳能作为能量来源的光催化CO₂还原技术更具应用前景。但是目前CO₂光还原催化剂仍然存在很多缺点,如可见光响应能力低、光生电子空穴对复合严重、CO₂吸附量小、产物的选择性低以及在含水环境中的产氢竞争反应等。金属-有机框架(MOFs)是由金属离子/簇和有机配体构成的一类独特的多孔晶态材料,具有可调的多孔结构、电子迁移速度快、CO₂吸附量大等优点,在光催化CO₂还原领域具有广阔的应用潜力。现有方法主要是通过对MOFs的功能化修饰、与其他功能型材料复合等获得高效的光还原CO₂的催化性能。本文主要对近年来MOFs基CO₂光还原催化剂(单一MOFs、MOFs基复合材料以及MOFs衍生材料)的研究现状进行了分析和讨论,并对MOFs材料在光催化CO₂还原中的发展趋势进行了展望。     

Stereochemically Rich Polycyclic Amines from the Kinetic Resolution of Indolines through Intramolecular Povarov Reactions

Under control of a chiral Brønsted acid catalyst, racemic indolines undergo intramolecular Povarov reactions with achiral aromatic aldehydes bearing a pendent dienophile. One enantiomer of the indoline reacts preferentially, resulting in the highly enantio‐ and diastereoselective formation of polycyclic heterocycles with four stereogenic centers. This kinetic resolution approach exploits the differential formation/reactivity of diastereomeric ion pairs.