用119Sn、121Sb及13C NMR研究无水SnCl4、SbCl5与Lewis碱的相互作用

无水SnCl₄及SbCl₅是典型的Lewis酸,是有机反应中常用的催化剂。它们的溶剂化热效应早已受到人们的关注,然而用NMR方法来研究它们的溶剂化作用至今未见报道。本工作用¹¹⁹Sn、¹²¹Sb及(13)C NMR考察了典型Lewis酸无水SnCl₄、SnCl₅与二十几种Lewis碱的相互作用,直接证实了Lewis酸碱反应为电子的授受过程。     

有机碲化合物的~(125)Te NMR研究

本文测定了三个有机碲盐化合物以及一些碲醚类化合物的~(125)Te NMR谱。得到了这些化合物的~(125)Te化学位移值。主要讨论了影响~(125)Te化学位移的因素。通过实验,我们可以得出如下的结论:与Te相连取代基的电负性增强,~(125)Te化学位移值增大。化合物中,碲的成键性质不同,~(125)Te化学位移值也有所不同。碲盐类化合物的~(125)Te化学位移值受溶液浓度及溶剂性质的影响比较大,浓度加大,~(125)Te化学位移向高场移动,而且变化较明显。溶剂的极性增强,~(125)Te化学位移向低场移动。     

全氟烷基芳基酮的合成

本文用8种取代苯基卤化物,在无水四氢呋喃中制成的格氏试剂与全氟羧酸(R_FCO_2H,R_F=CF_3和n-C_3F_7)按 3:1摩尔比反应,合成了9种全氟烷基芳基酮(1～9),其中6、7、8和9是新化合物。它们的结构用IR、UV、NMR(~1H,~(19)F)及MS加以表征。     

双核锡配合物[Sn_2Cl_6(μ-OH)_2(DMF)_2]·_4 DMF的合成和晶体结构

SnCl_4作为有机合成的重要催化剂受到人们的广泛关注.由于SnCl_4衍生的配位化合物中的锡原子具有四配位和六配位的功能而受到人们的重视.已知DMF能与SnCl_4生成确定的SnCl_4·2DMF配合物.我们曾系统地研究了SnCl_4的水合水解产物及常用有机溶剂的溶剂化产物的~(119)Sn核磁共振谱.在用NMR研究SnCl_4与DMF(N,N-二甲基甲酰胺)的相互作用过程中,我们得到了一个新的产物.测定了它的晶体结构[Sn_2Cl_6(μ-OH)_2(DMF)_2]·4DMF.     

含R_2dtc配体Mo-Cu化合物的动态~(95)Mo NMR

本实验利用动态~(95)Mo NMR监测Mo-Cu系列化合物的形成过程,对反应CuCl+NaR_2dtc+MoO_nS,摩尔比3:3:1,溶剂为DMF;R=Et,n=0(Ⅰ);R=Me,n=0(Ⅱ);R=Et,n=2(Ⅲ)进行了研究,观察到具有不同簇骼的多种中间产物的存在及随反应进程相互转化等现象。     

一些单立方烷化合物MFe_3S_4(S_2CNR_2)_5(M=Mo,W)的~1H NMR研究

本文报道了一些单立方烷化合物MFe_3S_4(S_2CNR_2)_5(M=Mo,W;R_2=Me_2,Et_2,C_4H_8,OC_4H_8,C_5H_(10))的~1H NMR谱研究,结果表明与铁原子相连的配体的α-H产生了相当大的各向同性位移,它随温度升高而减少,基本上服从居里定律。本文还讨论了化合物中的配体间交换反应以及簇骼中金属原子间耦合作用对配体的NMR的影响。     

含氮配体铂配合物—宁辛铂的~1H~,~(13)C和~(195)PtNMR研究

本文测定了具有抗癌活性的含氮配体铂配合物——宁辛铂Pt(C_8H_(18)N_2)(CICH_2COO)_2的~1H,~(13)C及~(195)Pt NMR谱,用DEPT及选择去偶等技术对~1H,~(13)C谱线进行了归属,并用位移理论和经验规律对~(195)Pt NMR化学位移进行了初步探讨,从而进一步确证了该化合物双齿配位的平面正方形结构。     

2,4-二酮-5-咪唑烷基尿的~(15)N和~(13)C核磁共振研究

本实验测定了2.4-二酮-5-咪唑烷基尿的~(15)N和~(13)C NMR谱并确认了谱线归属。根据化学位移及其在脱质子化过程中的变化,讨论了化合物的互变异构平衡及立体构型的转化问题。结果表明,在溶液中此化合物以酮式结构(A)为主要构型。     

手性高烯丙基胺的合成及表征——一个微量不对称合成教学实验

描述了一个以立体化学中非对映选择性为知识重点,以无水无氧操作为操作重点的微量不对称合成实验。(R)-N-叔丁基亚磺酰亚胺在无水无氧环境中,经过锌参与的烯丙基化,在不同的溶剂、添加剂条件下以不同的选择性得到了一对非对映异构体,以较高的产率得到终产物。烷基化反应产物的非对映体比率(dr)通过1H与19F NMR以及手性HPLC确定。总体来说,这一实验所用试剂易得,反应条件温和,速率快,产率高;学生在学习无水无氧操作(Schlenk技术)的同时,还能够熟悉立体化学的基本概念,了解如何通过调节反应溶剂和添加剂实现立体化学结果的逆转,并掌握使用手性HPLC和NMR确定光学活性物质的dr值的方法。     

几种抗菌素的~1H 和~(13)C NMR 谱的研究

测定和解析了氧哌嗪青霉素酸等六种抗菌素的~1H NMR 谱和~(13)C NMR 谱的宽带去偶谱、偏共振谱和全偶合谱以及偶合常数~3J_(HH)和~1J_(CH).除氧哌嗪青霉素酸和羟哌唑头孢菌素酸的~1H NMR 已有报道外,其余尚未见报道.实验用 FX-60Q 脉冲 Fourier 变换核磁共振仪测定(磁场强度14093G,观察频率:~1H NMR谱59.80MHz;~(13)C NMR 谱15.04MHz).样品皆由太原制药厂研究所合成,以氘代二甲基亚     

Diastereoselectivity in the Mukaiyama-Michael Reaction Employing alpha-Acyl beta,gamma-Unsaturated Phosphonates

The unique electronic and structural nature of the alpha-acylphosphonate functional group affords both dimeric and chelated complexes of diethyl crotonyl phosphonate (1; DECP) with stannic chloride (SnCl(4)). The dimeric complex, SnCl(4).(DECP)(2) (5) results from the coordination of two DECP molecules, ligated via the phosphoryl oxygens to the tin atom. The chelated complex, SnCl(4).(DECP) (6), is best represented with both phosphoryl and carbonyl oxygens coordinated to the metal center. Both metal ligated and chelated complexes have unique (13)C (31)P, and (119)Sn NMR spectra. In complex 5, the (13)C NMR resonances attributed to the carbonyl carbons were shifted upfield of free DECP. A monocoordinating Lewis acid, BF(3).OEt(2), produced a similar chemical shift trend in both the (13)C and (31)P NMR spectra of the BF(3).DECP complex. Essentially quantitative yields and moderate diastereomeric excesses favoring anti (or trans) diethyl 6-phenyl-4,5-dimethyl-6-(trimethylsilyloxy)-2-dihydropyranphosphonate (3) and diethyl 5-phenyl-3,4-dimethyl-1,5-dioxopentanephosphonate (4) were obtained from both chelated and dimeric SnCl(4).(DECP)(n) (n = 1, 2) when treated with either diastereomeric (Z)- or (E)-1-phenyl-1-(trimethylsilyloxy)-1-propene 2. Diethyl crotonylphosphonate (1), 3, and 4 were fully characterized.     

Optical basicity scales in protic solvents: water, hydrogen fluoride, ammonia and their mixtures

In an inorganic material, a measure of the Lewis basicity of a solvent is commonly provided by the optical basicity, i.e. the ability of the solvent molecules to donate their electrons to an acidic species. This quantity is known to vary with the polarizability of the Lewis base. In protic solvents, the Lewis definition of basicity is barely used; it is replaced by the more purpose-built Br?nsted-Lowry scale, and its generalized variant proposed by Hammett. In this study, individual molecular polarizabilities were computed from first-principles for a series of protic solvents: pure water, hydrogen fluoride, ammonia and their mixtures. From these calculations optical basicity scales were set up for each Lewis base. It was shown that these scales correlate with the Hammett acidity. It is therefore possible to build a common optical basicity scale, in which any material (protic solvents, inorganic materials) can unambiguously be classified.     

Ab Initio Molecular Dynamics with Explicit Solvent Reveals a Two‐Step Pathway in the Frustrated Lewis Pair Reaction

The role solvent plays in reactions involving frustrated Lewis pairs (FLPs)—for example, the stoichiometric mixture of a bulky Lewis acid and a bulky Lewis base—still remains largely unexplored at the molecular level. For a reaction of the phosphorus/boron FLP and dissolved CO₂ gas, first principles (Born–Oppenheimer) molecular dynamics with explicit solvent reveals a hitherto unknown two‐step reaction pathway—one that complements the concerted (one‐step) mechanism known from the minimum‐energy‐path calculations. The rationalization of the discovered reaction pathway—that is, the stepwise formation of P?C and O?B bonds—is that the environment (typical organic solvents) stabilizes an intermediate which results from nucleophilic attack of the phosphorus Lewis base on CO₂. This finding is significant because presently the concerted reaction‐path paradigm predominates in the rationalization of FLP reactivity. Herein we point out how to attain experimental proof of our results.     

Metal‐Free Hydrogenation Catalyzed by an Air‐Stable Borane: Use of Solvent as a Frustrated Lewis Base

In recent years ‘frustrated Lewis pairs’ (FLPs) have been shown to be effective metal‐free catalysts for the hydrogenation of many unsaturated substrates. Even so, limited functional‐group tolerance restricts the range of solvents in which FLP‐mediated reactions can be performed, with all FLP‐mediated hydrogenations reported to date carried out in non‐donor hydrocarbon or chlorinated solvents. Herein we report that the bulky Lewis acids B(C₆Cl₅)_x(C₆F₅)_3?x (x=0–3) are capable of heterolytic H₂ activation in the strong‐donor solvent THF, in the absence of any additional Lewis base. This allows metal‐free catalytic hydrogenations to be performed in donor solvent media under mild conditions; these systems are particularly effective for the hydrogenation of weakly basic substrates, including the first examples of metal‐free catalytic hydrogenation of furan heterocycles. The air‐stability of the most effective borane, B(C₆Cl₅)(C₆F₅)₂, makes this a practically simple reaction method.     

Formation of 3-aryl-5-nitroisocoumarins from 5-nitroisocoumarins and aromatic acyl chlorides under Friedel-Crafts conditions

Treatment of 5-nitroisocoumarin with aromatic acyl chlorides under Friedel-Crafts conditions gives 3-aryl-5-nitroisocoumarins, rather than the expected 4-acyl-5-nitroisocoumarins. This procedure was optimized for reaction temperature (150 degrees C), solvent (nitrobenzene), and Lewis acid (SnCl4). Reaction of 5-nitroisocoumarin with [13C]-carbonyl benzoyl chloride under the optimum conditions gave 5-nitro-3-phenylisocoumarin in which the 13C is located at the 3-C of the heterocycle, indicating that the benzoyl carbon framework is incorporated intact.     

Aza-Baylis-Hillman reactions of diisopropyl azodicarboxylate or diethyl azodicarboxylate with acrylates and acrylonitrile

It has been found that in the Baylis-Hillman reactions of DIAD or DEAD with acrylates or acrylonitrile, the Lewis base and solvent can significantly affect the reaction rate. Using DABCO as Lewis base in DMF or THF, the corresponding aza-Baylis-Hillman adducts 2 or 3 can be obtained in moderate to good yields.     

A computational study on the capability of borane‐cyclic boryl anion adducts to act as hydrogen atom donors

According to our theoretical approaches, a cyclic boryl anion can act as a Lewis base like its isoelectronic counterpart N‐heterocyclic carbene, reducing the homolytic bond dissociation energy of B? H in BH₃. However, the donating efficiency is affected by the counter cation in both gas phase and nonpolar solvents. Moreover, we also predict the seven‐membered ring boryl anion 5 , although it has not yet synthesized, to be the most efficient reagent to reduce the bond dissociation energy of a B? H bond in BH₃. This study may thus pave another avenue toward Lewis base induced hydrogen atom abstraction in BH₃. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Direct Chemoselective Synthesis of N-3-Substituted Pyrimidinones in a Microwave-Assisted Method

Synthesis of selectively N-3-substituted pyrimidine nucleobases or pyrimidinones has always been a challenge because of poor regioselectivity and chemoselectivity. In this article we demonstrate a single-step, de novo synthesis of selectively N-3-substituted modified pyrimidinones. We have developed a microwave-assisted methodology for direct, chemoselective alkylation, benzylation, and arylation of C-5 and C-6 substituted pyrimidine nucleobases selectively at the N-3 position. The reactions were found to proceed, with high efficiency, without the requirement of solvent and were complete within 10–15 min of irradiation. The efficiency of the method was further improved by addition of a Lewis acid, which not only increases the yield significantly but also accelerates the reaction rate.     

Bifunctional Gyroidal MOFs: Highly Efficient Lewis Base and Lewis Acid Catalysts

A family of gyroidal metal–organic frameworks (STUs) composited with transition metal ions and bi‐imidazolate ligands (BIm) were prepared and applied as both Lewis base and acid catalysts. Benefiting from the intrinsic basicity of the ligands and the Lewis acidic sites of the open metal centres, the STUs materials show excellent catalytic activities as Lewis base for the Knoevenagel condensation reaction between various aldehydes and malononitrile, and as Lewis acid for cyanosilylation reactions. Among these STUs, STU‐4 (Ni(BIm)) shows the best catalytic efficiency (conversions >99 %) in both Knoevenagel condensation and cyanosilylation reactions under mild conditions, providing thus an advanced material for both Lewis base and Lewis acid catalysis.