Chiral monodentate phosphine ligand MOP for transition-metal-catalyzed asymmetric reactions

Chiral monophosphines, whose chirality is due to biaryl axial chirality, have been prepared from enantiomerically pure 2, 2'-dihydroxy-1,1'-binaphthyl and demonstrated to be highly efficient chiral ligands for transition-metal-catalyzed organic transformations, especially for reactions where chelating bisphosphine ligands cannot be used. The high efficiency is observed in palladium-catalyzed asymmetric hydrosilylation of a wide variety of olefins such as alkyl-substituted terminal olefins and in asymmetric reactions via pi-allylpalladium intermediates represented by asymmetric reduction of allylic esters with formic acid.     

手性噁唑啉配体及其在不对称催化反应中的应用

综述了各种手性恶唑配体及其在不对称环丙烷化等催化反应中的应用。     

Chiral N,N'-dioxides: new ligands and organocatalysts for catalytic asymmetric reactions

Homochiral catalysts that can effect asymmetric transformations are invaluable in the production of optically active molecules. Researchers are actively pursuing the design of new ligands and organocatalysts by exploiting concepts derived from the application of bifunctional and C(2)-symmetric catalysts. Many homochiral catalysts containing amines, ethers, alcohols, and phosphines as electron-pair donors have been successfully developed. Amine N-oxides are highly polar substances. Despite their pronounced capacity as electron-pair donors, N-oxides have been underutilized in asymmetric reactions; they have only made a visible impact on the field in the preceding decade. Systematic studies have instead largely focused on pyridine- or quinoline-based scaffolds in organosilicon and coordination chemistry. The application of chiral tertiary amine N-oxides has not been widely pursued because of the difficulty of controlling the chirality at the tetrahedral nitrogen of the N-oxide moiety. In this Account, we outline the design of a new family of C(2)-symmetric N,N'-dioxides from readily available chiral amino acids. We then discuss the application of these chiral amine N-oxides as useful metal ligands and organocatalysts for asymmetric reactions. The high nucleophilicity of the oxygen in N-oxides is ideal for organocatalytic reactions that rely on nucleophilic activation of organosilicon reagents. These catalysts have been successfully applied in the asymmetric addition of trimethylsilylcyanide to aldehydes, ketones, aldimines, and ketimines, with good yields and excellent enantioselectivities. Asymmetric organocatalytic chlorination of β-ketoesters with N-chlorosuccinimide has also been achieved through hydrogen bond activation. The molecular framework of these N,N'-dioxides, with their multiple O-donors, also serves as a new tetradentate ligand that can coordinate a range of metal ions, including Cu(I), Cu(II), Ni(II), Mg(II), Fe(II), Co(II), In(III), Sc(III), La(III), Y(III), Nd(III), and others. These versatile metal complexes are efficient catalysts for a variety of asymmetric reactions. Asymmetric cycloadditions have been achieved with these chiral Lewis acid catalysts. We have also found success with asymmetric nucleophilic additions to C═O or C═N bonds; substrates include 3-substituted 2-oxindoles, alkenes, enamides, enecarbamates, diazoacetate esters, nitroalkanes, glycine Schiff bases, and phosphate. Notably, the first catalytic asymmetric Roskamp reaction was realized, which was successful because of the high efficiency of the catalyst. Asymmetric conjugate additions between α,β-unsaturated compounds and nucleophiles such as nitroalkane, malonate, thioglycolate, and indoles have been accomplished. The first asymmetric haloamination of chalcones was discovered, and the reaction proceeded with high regio- and enantioselectivity. In some cases, we were able to reduce the catalyst loading to just 0.01-0.05 mol % while maintaining excellent outcomes. Some particularly interesting phenomena were observed over the course of the research. These include a remarkable amplification of the asymmetry in a sulfa-Michael reaction, as well as the reversal of enantioselectivity after alteration of the central metal or the subunits of the ligand in two other reactions. These unusual results have facilitated a deeper understanding of the catalytic mechanism.     

Dipeptides from methionine and S-methylcysteine as chiral ligands for asymmetric Michael reactions

Dipeptides derived from methionine and S-methylcysteine 3a – d have been prepared and screened as chiral ligands in combination with 13 metal salts 4a – m towards the catalysis of an asymmetric Michael reaction of a β-keto ester 1 with methyl vinyl ketone 2 resulting in an optimal ee of 18% achieved with FeCl₃ · 6 H₂O 4c as the metal salt.     

P-Phos: a family of versatile and effective atropisomeric dipyridylphosphine ligands in asymmetric catalysis

This Account outlines our efforts in the design and synthesis of a family of highly effective atropisomeric dipyridylphosphine ligands (P-Phos and its variants) and in the development of their widespread applications in transition-metal-catalyzed asymmetric reactions including hydrogenation, hydrosilylation, and C-C bond formation. Desirable attributes, such as air stability, broad substrate scope, fast rates of reaction, excellent enantioselectivities, low catalyst loading, and mild conditions, make the catalyst systems highly attractive and thus may provide excellent opportunities for practical applications.     

Amino acid derived amides and hydroxamic acids as ligands for asymmetric transfer hydrogenation in aqueous media

Amides and hydroxamic acids derived from α-amino acids were evaluated as ligands in combination with rhodium and iridium half-sandwich complexes in asymmetric transfer hydrogenation (ATH) of ketones. The reactions were performed in aqueous media using lithium formate as hydride source. The catalyst systems turned out to be highly efficient and ee's up to 90% were obtained.     

Chiral salen Mn(III) immobilized on sulfoalkyl modified ZSP-IPPA as an effective catalyst for asymmetric epoxidation of unfunctionalized olefins

Sulfoalkyl modified zirconium poly (styrene-isopropenyl phosphonate)-phosphate (ZPS-IPPA), with special structures of new type of organic–inorganic hybrid material were designed and synthesized for immobilization of the chiral salen Mn(III) Jacobsen’s homogenous catalyst by axial coordination. All the heterogeneous chiral salen Mn(III) catalysts with different linkage lengths obtained exhibited great catalytic activity and enantioselectivity in the asymmetric epoxidation of unfunctionalized olefins. The influence of the linkage lengths on the catalytic performance was investigated. What’s more, the catalysts were easily separated from the reaction systems and could be reused for several times without significant loss of catalytic activity.     

An efficient protocol for copper- and amine-free Sonogashira reactions catalyzed by mononuclear palladacycle complexes containing bidentate phosphine ligands

An efficient protocol for copper- and amine-free Sonogashira coupling of aryl halides with phenylacetylene in mild reaction conditions under air is reported using moisture/air-stable and robust palladacycle phosphine complexes as catalyst precursors. The use of 0.001 mol% catalysts in the presence of Cs₂CO₃ allows the coupling reaction to proceed with moderate to good yields. Also, ³¹P NMR studies showed that palladacycle 1 can be reduced to zerovalent palladium in methanol, by forming dppe dioxide.     

由氟化锂和五氯化磷制备五氟化磷的动力学研究

在150~195 ℃下,研究了氟化锂和五氯化磷制备五氟化磷的反应过程,并应用缩芯模型处理数据,确定了反应的动力学模型：反应初期（0～0.5 h）,该反应受化学反应控制,动力学方程为k_s=22.2exp[-34 490/(R_gT)];反应后期（1～3 h）,该反应主要受内扩散控制,动力学方程为D_e=4.357×10^-7exp[-29 980/(R_gT)]。该研究旨在揭示氟化锂和五氯化磷制备五氟化磷反应过程的相关规律,为工业生产五氟化磷提供必要的基础数据。     

厌氧释磷量和温度对反硝化聚磷的影响

为了提高双污泥系统的脱氮除磷效率,以反硝化除磷污泥为研究对象,采用静态试验进行对比研究,考察了厌氧释磷量和温度对缺氧反硝化聚磷的影响。结果表明:在试验范围内,随着厌氧释磷量的增加,反硝化聚磷量、净聚磷量和硝氮去除效率增加,聚磷量与释磷量之比基本不变。在8、16、28℃三种情况下,均在约260min时结束反硝化聚磷,低温下反硝化聚磷效果显著下降。在各试验条件下,NO-3-N去除量与PO34--P去除量均呈良好的线性关系,系数为1.002~1.044,体现了系统中污泥的固有特性。     

Enantioselectivity promotion by achiral surface functionalization on SiO2-supported Cu-bis(oxazoline) catalysts for asymmetric Diels–Alder reactions

Novel SiO₂-supported chiral Cu-bis(oxazoline) (BOX) complexes for asymmetric Diels–Alder reactions were prepared by combining metal-complex immobilization with surface functionalization using achiral silane-coupling reagents on SiO₂. We found that the surface functionalization of a SiO₂-supported Cu-BOX catalyst with achiral 3-methacryloxypropyltrimethoxysilane dramatically increased enantioselectivity in the asymmetric Diels–Alder reaction of cyclopentadiene and 3-acryloyl-2-oxazolidinone. The Cu-BOX complexes on bare and functionalized SiO₂ surfaces were characterized by XAFS, ESR, FT-IR, UV/vis, and ²⁹Si solid-state MAS NMR. The large increase in enantioselectivity by achiral surface species without chiral center may be due to a glue effect, creating a new chiral ensemble structure at the surface.     

Ruthenium catalyzed asymmetric transfer hydrogenation based on chiral P,N,O Schiff base ligands and crystal structure of a ruthenium(II) complex bearing chiral P,N,O Schiff base ligands

A ruthenium catalyst, generated in situ by heating the chiral P,N,O Schiff base ligand L (L = (S)-Ph₂PC₆H₄CNCHPhCH₂OH) with Ru(DMSO)₄Cl₂ in 2-propanol, is active for asymmetric transfer hydrogenation with best enantioselectivity up to 81%. A ruthenium complex of formula RuL₂Cl₂ is prepared and its crystal structure revealed that the two chiral P,N,O Schiff ligands are in meridional configuration. This complex is also an active catalyst for asymmetric transfer hydrogenation. However, the ‘[Ru(DMSO)₄]Cl₂ + chiral P,N,O ligand’ protocol displays better enantioselectivity.     

Inorganic phosphorus and manure effects on bahiagrass production on a Spodosol

Bahiagrass (Paspalum notatum Flugge) pasture fertilization recommendations have traditionally been based upon clipping studies. Inclusion of P from manure, not originally considered when P recommendations were developed for pastures, may minimize the need for P fertilization without reducing bahiagrass production or P uptake. The objective of this research was to determine if manure contributes greatly to the P crop nutrient requirement. A 2-year field study utilized a factorial arrangement of 0 and 6.9 Mg air-dried manure ha^-1 with 0, 17, 34, 51, and 68 kg inorganic P ha^-1 from triple superphosphate to evaluate bahiagrass yield, root distribution, and P uptake response on a Myakka fine sand (sandy, siliceous, hyperthermic Aeric Alaquod). Because air-dried manure was used in the field study, a greenhouse study was employed to confirm that there were no differences in bahiagrass yield or P uptake from either air-dried or fresh cattle (Bos spp.) manure sources. There were no manure or manure by P interaction effects on yield or P uptake of bahiagrass indicating that manure source did not effect grass production in the greenhouse. In the field study, bahiagrass roots were distributed into the Bh horizon, and the Bh horizon had at least four times more Mehlich-1 extractable P than that of the Ap horizon. This horizon was most likely acting as a main source for P-uptake by the grass. This observation was further confirmed by no yield response to levels of inorganic P application in 1989. A linear-response-and-plateau (R²=0.196) relationship with a critical point of 15.4 kg P ha^-1 was found in 1990. Bahiagrass yield and P uptake were not dependent on P fertilization, either from manure or inorganic P, due to the availability of P from the Bh horizon.     

Nutrient budgeting for phosphorus and potassium in a long-term fertilizer trial

Influence of N, P and K application through inorganic and organic fertilizers on P and K removal in crop plants, changes in soil fertility status and their balance in the soil-plant (maize-wheat-cowpea fodder) studied for the first 22 years of a long-term experiment at Punjab Agricultural University farm, Ludhiana, India. The results showed that P uptake by wheat was about 1.5 times that of maize, whereas K uptake by wheat was only 1.1 times that of maize. The apparent P recovery by both maize and wheat depended on the rates of N, P and K application. Fertilizer rates greater than the recommended (150% NPK) resulted in lower P recoveries. At optimum level of N, P and K application (100% NPK) the mean P recovery (for 22 years) was 30.3% (±5.47) in wheat as compared to 20% (±11.35) in maize. The apparent P recovery in maize declined as the number of cropping years progressed. In 100% NPK plots, it declined from 45.6% in 1973 to 12.5% in 1992. The decline in P recovery was due to the accumulation of plant available P in the soil which increased from the initially low status to high-very high due to continuous application of P fertilizer. The application of FYM in conjunction with 100% NPK led to significantly greater accumulation of available P as compared to 100% NPK treatment alone despite the higher amount of total P removal in the former treatment than that from the latter. A trifle build-up in available K was observed in K amended plots notwithstanding the negative balance of K based on the approach of input-output relationship. The release of K from non-exchangeable form contributed towards K uptake by the crops. The results suggested the need for modifying the existing K fertilizer recommendations to compensate for gradual loss of native soil K fertility.     

Engineering and functionalization of the disulfide-constrained miniprotein min-23 as a scaffold for diagnostic application

Miniproteins are scaffolds for the development of alternative non‐immunoglobin binding agents for medical applications. This peptide format features high tolerance to sequence mutagenesis, excellent proteolytic stability, and fast blood pool clearance. Herein we present the total chemical synthesis of the disulfide‐constrained scaffold Min‐23 and its functionalization for in vitro and in vivo application. Optimized solid‐phase peptide chemistry and oxidative folding strategies were developed to engineer this miniprotein with native‐like disulfide configuration. High levels of serum stability and proteolytic resistance, as well as a beneficial pharmacokinetic profile for diagnostic imaging, were determined by using radiolabeling techniques such as positron emission tomography. The reported achievements highlight Min‐23 as a promising scaffold for the development of novel recognition molecules for medical application.     

手性咪唑环芳识别氨基酸甲酯的作用模式研究

采用Gaussian 03在B3LYP/6-31G(d)水平上分别优化手性咪唑环芳受体和氨基酸甲酯配体,并在同样条件下计算NBO电荷。用AutoDock Vina将优化后的受体、配体进行对接,获得相应复合物的最稳定构象。以复合物亲和能和配体侧链电子电荷指数,建立了表达复合物稳定常数的定量关系模型。从单体的NBO电荷分布、复合物最稳定构象等方面分析探讨,发现静电吸引、受体配体间的空间匹配和氢键作用等,是影响手性咪唑环芳选择性识别氨基酸甲酯的主要影响因素。     

Effect of fertilizer type,sampling depth,and years on Colwell soil test phosphorus for phosphorus leaching soils

The relationships between (i) soil test phosphorus (P) (Colwell sodium bicarbonate procedure) and the level of P applied (from 0 to 1000 kg total P ha^–1) (relationship 1), and (ii) yield and soil-test P (relationship 2, the soil P test calibration), were measured in two field experiments on very sandy, P-leaching soils in the high rainfall (> 800 mm annual average) areas of south-western Australia. The soils were humic sandy podzols, or haplohumods, comprising 97% sand (20 to 2000 m). The experiments started in April 1984 and were terminated at the end of 1990. Soil-test P, measured on soil samples collected to 5, 10 and 25 cm depth each January in the years after P application, was related to yields of dried clover (Trifolium subterraneum) herbage measured later in each year. The four P fertilizers studied were single superphosphate, coastal superphosphate (made by adding, just before granulation, extra rock phosphate together with elemental sulphur while manufacturing single superphosphate), apatite rock phosphate, and Calciphos.Relationship (1) was adequately described by a linear equation (R² > 0.80, most being > 0.90). The slope coefficient estimates the extractability of P from the soil by the Colwell procedure, and is called extractability. Relationship (2) was adequately described by the Mitscherlich equation (R² > 0.75, most being > 0.90). For relationship (2), use of percentage of the maximum (relative) yield eliminated differences due to different maximum yields and yield responses (maximum yield minus the yield for the nil-P treatment). Soil test P ranged from about 4 to 150 g Pg^–1 soil. Soil test P and extractability were generally higher for samples of the top 5 cm of the soil than the top 25 cm, and were largest for single superphosphate and lowest for apatite rock phosphate. Both extractability (relationship (1)) and the curvature coefficient of the Mitscherlich equation (relationship (2)), differed for different P fertilizers and different soil sample depths. The curvature coefficient also differed for different yield assessments (harvests) in the same or different years. Different soil P test calibrations were required for different P fertilizers, soil sample depths and harvest in the same or different years. It is concluded that soil P testing provides a crude estimate of the current P status of P-leaching soils in Western Australia.     

Effective and Reusable Pt Catalysts Supported on Periodic Mesoporous Resols for Chiral Hydrogenation

Platinum nanoparticles supported on periodic mesoporous resols by simple impregnation serve as effective, robust and remarkably reusable catalysts after chirally modified with cinchonidine for the asymmetric hydrogenation of ethyl pyruvate, affording up to 62% enantiomeric excess (ee) and a constant activity after 25th re-use. They can also catalyze the reaction in an environmentally benign manner by using water as a solvent.