唑硼烷催化前手性酮不对称还原反应机理的量子化学研究

对手性唑硼烷催化3,3-二甲基丁酮-2不对称还原反应机理进行了从头算研究.结果表明,该不对称还原反应是放热的.反应经历了催化剂-硼烷加合物、催化剂-硼烷-酮加合物、含B-O-B-N四元环的催化剂-烷氧基硼烷加合物的生成,以及催化剂-烷氧基硼烷加合物的离解并再生催化剂等过程.在催化剂-硼烷-酮加合物经氢转移而生成催化剂-烷氧基硼烷加合物的过程中,氢转移与B-O-B-N四元环的形成是协同进行的.氢转移是还原反应的控制步骤.氢转移过渡态具有扭曲的椅式结构,所决定的还原产物是与实验相吻合的R手性醇.     

用于乙烯齐聚高选择性制 1-辛烯反应的Cr(Ⅲ)基催化剂体系

将四元催化剂体系(乙酰丙酮铬-膦胺型配体-助催化剂甲基铝氧烷-促进剂六氯乙烷)用于乙烯齐聚制1-辛烯反应,考察了促进剂、助催化剂、Al/Cr摩尔比、反应温度和反应压力等对催化剂的活性和1-辛烯的选择性的影响.结果表明,该四元催化剂体系比三元催化剂体系(铬化合物-膦胺型配体-甲基铝氧烷)对乙烯齐聚反应具有更高的1-辛烯选择性.产物除有1-辛烯外,还有较大量的1-己烯、甲基环戊烷和亚甲基环戊烷.甲基铝氧烷是高选择性生成1-辛烯必不可少的助催化剂.作为促进剂的六氯乙烷可以使乙酰丙酮铬更有利于催化乙烯齐聚反应生成1-辛烯.     

噁唑硼烷催化前手性酮不对称还原反应机理的量子化学研究

对手性噁唑硼烷催化3,3-二甲基丁酮-2不对称还原反应机理进行了从头算研究.结果表明,该不对称还原反应是放热的.反应经历了催化剂-硼烷加合物、催化剂-硼烷-酮加合物、含B-O-B-N四元环的催化剂-烷氧基硼烷加合物的生成,以及催化剂-烷氧基硼烷加合物的离解并再生催化剂等过程.在催化剂-硼烷-酮加合物经氢转移而生成催化剂-烷氧基硼烷加合物的过程中,氢转移与B-O-B-N四元环的形成是协同进行的.氢转移是还原反应的控制步骤.氢转移过渡态具有扭曲的椅式结构,所决定的还原产物是与实验相吻合的R手性醇.     

纳米Au/ZSM-5催化剂的制备及其对分子氧氧化β-紫罗兰酮的催化性能

利用硝基甲烷还原法制备了一系列不同粒径的纳米Au颗粒,用浸渍法担载于ZSM-5分子筛上制得Au/ZSM-5催化剂,并考察了其对分子氧氧化β-紫罗兰酮的催化性能.结果发现,该催化剂可以有效地催化分子氧氧化β-紫罗兰酮生成5,6-环氧-β-紫罗兰酮、4-氧代-β-紫罗兰酮、4-羟基-β-紫罗兰酮以及少量的二氢猕猴桃内酯,这些产物均是优质的香料及其前体.与传统的铬盐催化剂相比,本文制备的催化剂可选择性地将β-紫罗兰酮氧化为环氧化合物,并且反应后催化剂容易分离.详细探讨了不同载体、氧化剂、溶剂、反应温度和反应时间对β-紫罗兰酮氧化反应的影响.结果表明,催化剂的催化性能与担载金的颗粒大小密切相关,同时溶剂的性质也对反应有明显影响.以氯仿为溶剂时催化剂催化性能最好.催化剂循环使用五次仍具有较高的催化活性.     

纳米丝负载钯催化剂的制备及催化烯烃加氢性能研究

利用电纺丝技术制备出苯乙烯-丙烯腈共聚物负载钯的纳米丝催化剂.对催化剂进行了SEM、TEM、IR和XPS的测试.所制备的催化剂对α-己烯催化氢化结果表明,该催化剂在常温、氢气常压下具有很高的催化活性和较好的重复使用性,并且催化氢化过程中存在烯烃的异构化反应.实验结果表明,反应时间为150min时纳米催化剂A对α-己烯催化加氢生成正己烷的转化率是传统催化剂PdCl2/-γAl2O3的4.7倍.     

Cr-Cu/SiO2 催化剂上顺酐和1,4-丁二醇的耦合反应

研究了Cr-Cu/SiO2催化剂上顺酐加氢反应和1,4-丁二醇脱氢反应耦合制备重要的精细化学品γ-丁内酯.耦合反应显著提高了顺酐转化率和γ-丁内酯选择性.Cr修饰提高了催化剂的脱氢活性,抑止了催化剂的过度加氢活性,使1,4-丁二醇的转化率和γ-丁内酯选择性显著提高.Cr修饰量为w=5%的Cr-Cu/SiO2催化剂上耦合反应的原料转化率为100%,γ-丁内酯选择性达98.8%.XRD,XPS等研究表明,Cr修饰促进了催化剂上铜元素的分散,氧化铬对氧化铜有给电子作用,Cr修饰的Cr-Cu/SiO2催化剂还原后比Cu/SiO2具有更多的Cu ,这有利于催化剂脱氢活性和γ-丁内酯选择性的提高.     

非晶态Co-P-B催化剂在1-辛烯氢甲酰化反应中的应用

通过化学还原法制备了不同Co/P和P/B摩尔比的Co-P-B非晶态催化剂. 采用XRD, ICP-Mass和氮气吸附-脱附等温线对催化剂的性质进行了表征. 在5.0 MPa和120 ℃条件下, 以1-辛烯的氢甲酰化为模型反应, 对Co-P-B催化剂的活性进行了评价, 并与Co-B及Co-P催化剂进行了比较. 结果表明, 非晶态Co-P-B催化剂对1-辛烯氢甲酰化反应具有良好的活性和选择性. 催化剂中P, B和Co的摩尔比、结构及比表面积等性质影响催化剂的活性和选择性, 添加适量的P有助于提高转化率和选择性. 在Co-P-B(Co摩尔分数为85.4%, P摩尔分数为3.3%)催化剂上, 1-辛烯的转化率为97.2%, C9-醛的选择性达到99.5%.     

[N,N]-二齿镍配合物催化烯烃聚合

烯烃聚合催化剂的设计是烯烃配位聚合领域的一个核心科学问题,通过设计合成精确结构的催化剂可以有效地调控催化聚合性能以及聚合产物的结构.后过渡金属催化剂由于其易调变性、对聚合产物支化结构的可控性及对极性单体的容忍性,在烯烃聚合领域引起了广泛的关注.本文介绍了近年来本课题组在[N,N]-二齿镍烯烃聚合催化剂设计方面的研究进展,包括四元环的中性脒基镍催化剂、五元环的-二亚胺镍催化剂、2-胺基吡啶和-胺基亚胺系列镍催化剂,以及六元环的-二亚胺和苯胺基亚胺镍催化剂在烯烃聚合的应用.通过优化后过渡金属镍催化剂结构,可成功实施烯烃活性聚合.     

亚胺不对称催化还原的量子化学研究

对手性噁唑硼烷催化亚胺不对称还原反应进行了量子化学研究. 对反应中间体和过渡态进行了B3LYP/6-31G(d)全优化. 噁唑硼烷对亚胺还原的催化作用是显著的. 还原反应经历了催化剂-硼烷加合物、催化剂-硼烷-亚胺加合物、催化剂-氨基硼烷加合物的生成, 以及催化剂-氨基硼烷加合物的离解并再生催化剂等过程. 还原反应的速度控制步骤是噁唑硼烷-氨基硼烷加合物的离解. 理论预测的还原产物是与实验吻合的R-手性胺.     

新型Sn改性固体酸催化剂SO42-/TiO2催化1,6-己二醇二丙烯酸酯合成

丙烯酸酯单体包括通用丙烯酸酯和特种丙烯酸酯,不仅是高分子化合物的基本单体,也是化工有机反应的原料.特种丙烯酸酯在工业合成中虽然规模小,产量低,但已经应用到皮革、造纸、纺织、涂料、粘合剂和辐射固化技术等许多领域.辐射固化材料主要包括活性稀释剂、光引发剂、齐聚物和添加剂等.其中,齐聚物的主要成分就是丙烯酸酯单体的聚合物.然而,丙烯酸酯的合成工业难度不在合成路线,而是反应所使用的催化剂.浓硫酸和对甲苯磺酸等液体酸催化剂由于后续反应难分离、腐蚀设备、污染环境和催化剂不易回收等缺点,逐渐被固体酸催化剂所替代.而SO42-/MOx固体酸催化剂虽然没有这些缺点,但是催化剂比表面积较小,热稳定性较差,酸性难以调节.为了合成1,6-己二醇二丙烯酸酯,本文首先对多种催化剂进行了筛选,获得了活性高且稳定好的SO42-/TiO2-SnO2改性催化剂.采用N2吸附-脱附、X射线衍射(XRD)、扫描电镜(SEM)、红外光谱(IR)、吡啶红外、氨程序升温脱附和热重等技术考察了催化剂的结构特征、表面酸强度和热稳定性.通过N2吸附-脱附可知,Sn改性后催化剂的比表面积增加到126m2/g,较改性前有明显提高.XRD结果表明,Sn能较好地分散在催化剂载体表面,且随着Sn的加入,催化剂晶粒尺寸逐渐减小.SEM照片进一步证实了N2吸附-脱附和XRD结果.催化剂表面酸性通过吡啶红外和氨程序升温脱附测定.由IR图谱可知,固体酸催化剂SO42-/TiO2-SnO2中SO42-和金属原子的连接方式发生变化,更趋于螯合双齿配位结合.通过吡啶红外可以看出,当Sn添加量为6％时,改性催化剂的酸性位由未改性催化剂的59 μmol/g增加到167 μmol/g.氨程序升温脱附.结果表明,多次使用后催化剂的酸分布几乎不变,但酸量有所下降,这可能与催化剂表面硫源的损失有关.另外,通过热重对催化剂的热稳定性进行了分析,由于高温条件下孔结构容易坍塌导致硫源损失,因此第二个失重峰归属为SO42-的脱除峰.Sn改性后的催化剂中SO42-的脱除峰后移100℃左右,且失重量为5O42-/TiO2的2倍多,说明SO42-/TiO2-SnO2催化剂有更好的热稳定性和更多的酸性位.以1,6-己二醇和丙烯酸酯化反应中1,6-己二醇转化率和1,6-己二醇二丙烯酸酯收率为指标评价了催化剂的催化活性.主要研究了催化剂中Sn含量的影响,并对酯化反应条件进行了优化.结果表明,最适宜的Sn含量为6％,最优的反应条件为:酸/醇比3.5,催化剂添加量7％,酯化温度130℃,酯化时间3h.最后考察了改性催化剂的稳定性.结果表明,催化剂使用10次后,1,6-己二醇转化率仍可达81％以上,固体酸催化剂SO42-/TiO2-SnO2有良好的稳定性.     

Fluorogenic probes for aldol reactions: tuning of fluorescence using π-conjugation systems

Fluorogenic aldehydes or probes for monitoring of the progress of aldol reactions have been developed. Fluorescence of benzaldehydes conjugated with aryl groups via a double or triple bond and of their aldol products was evaluated in aqueous solutions. Based on the fluorescence, fluorogenic aldol reaction substrates and retro-aldol reaction substrates were identified. Use of the probe system with optimal fluorescence properties for aldol reactions was demonstrated in assays with purified protein catalysts and with overproduced crude protein catalysts in cell lysates.     

Proline and benzylpenicillin derivatives grafted into mesoporous MCM-41: Novel organic-inorganic hybrid catalysts for direct aldol reaction

New organic-inorganic hybrid catalysts were synthesized by covalent grafting of proline and benzylpenicillin derivatives into mesoporous MCM-41. These catalysts were extensively characterized using FT-IR,¹³C CP MAS solid stateNMR, XRD and TEM techniques. These were used as catalysts for direct, asymmetric aldol reaction between acetone and activated aromatic aldehydes. In the reaction of 4-nitro and 4-fluoro benzaldehyde, the aldol products were obtained in 36% and 59%ee respectively. The catalysts were reusable with neither significant drop in enantioselectivity nor loss of mesostructure. An attempt was made to substantiate the proposed ’enamine’ mechanism for direct aldol reaction by trapping the intermediate between proline-MCM-41 and acetone. Dedicated to Professor C N R Rao on his 70th birthday     

Direct asymmetric aldol reactions inspired by two types of natural aldolases: water-compatible organocatalysts and Zn(II) complexes

In this article the utility of water-compatible amino-acid-based catalysts was explored in the development of diastereo- and enantioselective direct aldol reactions of a broad range of substrates. Chiral C(2)-symmetrical proline- and valine-based amides and their Zn(II) complexes were designed for use as efficient and flexible chiral catalysts for enantioselective aldol reactions in water, on water, and in the presence of water. The presence of 5 mol % of the prolinamide-based catalyst affords asymmetric intermolecular aldol reactions between unmodified ketones and various aldehydes to give anti products with excellent enantioselectivities. We also demonstrate aldol reactions of more demanding substrates with high affinity to water (i.e., acetone and formaldehyde). Newly designed serine-based organocatalyst promoted aldol reaction of hydroxyacetone leading to syn-diols. For presented catalytic systems organic solvent-free conditions are also acceptable, making the elaborated methodology interesting from a green chemistry perspectives.     

Bronsted acid catalysis of achiral enamine for regio- and enantioselective nitroso aldol synthesis

Two types of chiral Br?nsted acid catalysts have been shown to catalyze regio- and enantioselective nitroso aldol synthesis between nitrosobenzene and achiral enamine. The combination of Br?nsted acidity and amine moiety of enamine realizes complete regioselectivity with high enantioselectivity. After a survey of Br?nsted acid catalysts, 1-naphthyl glycolic acid is found to be optimal in the O-nitroso aldol pathway, while 1-naphthyl TADDOL is the best catalyst for the N-nitroso aldol pathway. This is based on our finding on the control of regioselectivity by changing the amine moiety of enamine and the choice of Br?nsted acidity.     

Development of protein, peptide, and small molecule catalysts using catalysis-based selection strategies

We have developed peptide catalysts and antibody catalysts that catalyze aldol, retro-aldol, and Michael reactions via an enamine mechanism using reaction-based selections with 1,3-diketone derivatives. Nucleophilic amino groups of the catalysts were covalently trapped during the selections. We have also developed fluorogenic substrates that are useful for real-time monitoring of the progress of bond-forming reactions, such as aldol reactions, by an increase in fluorescence. These fluorogenic substrates have been used to monitor peptide-catalyzed, antibody-catalyzed, enzyme-catalyzed, and small molecule-catalyzed reactions. Catalysis-based screening using fluorogenic substrates will accelerate rapid identification of superior catalysts and reaction conditions.     

Elongation of β-hydroxyenones by cross-metathesis

Enantioenriched aldol products derived from enones are notoriously difficult to prepare due to their sensitivity to retro-aldolisation, elimination and the requirement of a large excess of the enone donor for their preparation. However, some success has been obtained for the preparation of aldol products derived from methylvinylketone and pentenone using zinc-dinuclear catalysts or catalytic antibodies. Herein, we describe how simple first-generation hydroxyenones can be easily elongated by alkene exchange with structurally diverse olefinic partners in the presence of Ru-based metathesis catalysts allowing for the preparation of aldol products difficult to access by direct aldolisation. The data suggest that even though unprotected aldols are suitable for these cross-metathesis reactions, silyl-protected β-hydroxyenones generally afforded the desired elongated products in much higher chemical yields.     

Novel chiral gallium Lewis acid catalysts with semi-crown ligands for aqueous asymmetric Mukaiyama aldol reactions

Asymmetric Mukaiyama aldol reactions in aqueous media (water-ethanol = 9:1) were catalyzed by chiral gallium catalysts with semi-crown ligands to give aldol products with good yields, syn-diastereoselectivities and enantioselectivities.     

Acetylphosphonate as a surrogate of acetate or acetamide in organocatalyzed enantioselective aldol reactions

Highly enantioselective aldol reactions of acetylphosphonates and activated carbonyl compounds was realized with cinchona alkaloid derived catalysts, in which the acetylphosphonate was directly used as an enolate precursor for the first time. The aldol product obtained was converted in situ to its corresponding ester or amide through methanolysis or aminolysis. The overall process may be viewed as formal highly enantioselective acetate or acetamide aldol reactions, which are very difficult to achieve directly with organocatalytic methods.     

N-heterocyclic carbene-catalyzed Mukaiyama aldol reactions

N-Heterocyclic carbenes were shown to be highly effective catalysts to promote Mukaiyama aldol reactions. In the presence of only 0.5 mol % of N-heterocyclic carbene (5), various aldehydes and 2,2,2-trifluoroacetophenone underwent Mukaiyama aldol reactions in THF with trimethylsilyl ketene acetal (2) at 23 degrees C as well as with trimethylsilyl enol ether (7) at 0 degrees C to afford aldol adducts in good yields. These conditions are extremely mild and operationally simple and tolerate various functional groups. [reaction: see text]     

Zinc-prolinamide complex catalyzed direct asymmetric aldol reactions in the presence of water

An efficient direct asymmetric aldol reaction with zinc triflate and prolinamides as combined catalysts is reported. A series of chiral prolinamides have been designed and used in the direct aldol reaction resulting in the desired products with excellent yields (up to 94% yield) and high enantioselectivities (up to 96% ee). Water was found to play a significant role in the formation of the aldol products, which suggests a new strategy in the design of new organic catalysts.