Take the Right Catalyst: Palladium-Catalyzed C-C, C-N, and C-O Bond Formation on Chloroarenes

Unreactive chloroarenes have been outwitted: The key to successful C-C, C-N, and C-O bond formation on chloroarenes is the development and optimization of suitable catalysts. Electron-rich alkylphosphanes are mandatory as ligands in these palladium-catalyzed reactions.     

Molecular Structure of Complexes with Bifurcated Hydrogen Bond: I. N-(4-Methyl-2-nitrophenyl)acetamide

According to the results of HF/6-31G* and B3LYP/6-31G* nonempirical calculations, N-(4-methyl- 2-nitrophenyl)acetamide in the synperiplanar and antiperiplanar conformations gives stable complexes with protophilic solvents, which are stabilized by bifurcated (three-center) hydrogen bond. The complexes are characterized by (1) opposite variations of the interatomic distances and angles corresponding to intra- and intermolecular components of the bifurcated hydrogen bond, (2) extension of the intramolecular component and a more pronounced shortening of the intermolecular component with increase in the strength of the three-center H-complex, and (3) nonlinear and nonmonotonic relation between the NH stretching vibration frequency and the energy of complex formation.     

Unparalleled,Enormous Metal–Carbon Bond Strength in PdCH2I+

Thermalized Pd⁺ cations activate methyl iodide by selective cleavage of a C? H bond under formation of PdCH₂I⁺ and an H-atom. This finding implies that the interaction energy between the metal cation and the CH₂I fragment and thus the metal–carbon bond strength exceeds 103 kcal/mol. Theory predicts that the energetically most favorable isomer of this ion exhibits the Pd⁺? CH₂? I structure, which is stabilized by an unprecedented bridging interaction between the two heavy atoms Pd and I.     

取代基对1-甲基尿嘧啶与N-甲基乙酰胺氢键复合物中氢键强度的影响

使用密度泛函理论B3LYP方法和二阶微扰理论MP2方法对由1-甲基尿嘧啶与N-甲基乙酰胺所形成的氢键复合物中的氢键强度进行了理论研究, 探讨了不同取代基取代氢键受体分子1-甲基尿嘧啶中的氢原子对氢键强度的影响和氢键的协同性. 研究表明: 供电子取代基使N－H…O＝C氢键键长r(H…O)缩短, 氢键强度增强; 吸电子取代基使N－H…O＝C氢键键长r(H…O)伸长, 氢键强度减弱. 自然键轨道(NBO)分析表明: 供电子基团使参与形成氢键的氢原子的正电荷增加, 使氧原子的负电荷增加, 使质子供体和受体分子间的电荷转移量增多; 吸电子基团则相反. 供电子基团使N－H…O＝C氢键中氧原子的孤对电子轨道n(O)对N－H的反键轨道σ^*(N－H)的二阶相互作用稳定化能增强, 吸电子基团使这种二阶相互作用稳定化能减弱. 取代基对与其相近的N－H…O＝C氢键影响更大.     

ZrCl4-Catalyzed C-O Bond to C-N Bond Formation: Synthesis of 1,2,3-Triazoles and Their Biological Evaluation

A simple and efficient protocol was developed for the synthesis of aryl azides directly from aryl carbinols using ZrCl₄ as a Lewis acid catalyst. The azides were converted to novel triazoles under click reaction conditions, which were evaluated for their antimicrobial activity against various strains.     

MoP(001)表面苯胺C―N键断裂机理

油品脱氮可以减少燃烧过程中氮氧化物的排放,并且减弱催化剂的中毒现象,过渡金属磷化物因具有高催化活性和优异的稳定性而成为最具应用前景的新型加氢脱氮(HDN)催化剂。本工作基于周期性平板模型,通过密度泛函理论(DFT)计算研究了苯胺在磷化钼(MoP)(001)表面的吸附以及C―N断键机理。结果表明在MoP(001)表面,苯胺吸附以平躺吸附构型为主,有较大的吸附能,C―C键和C―N键均被吸附活化;苯胺C―N键的直接断裂路径主要起始于与共吸附H_2发生反应,产物为苯和氨,吸附的环己胺的C―N键断裂主要路径是环己胺与共吸附的H发生反应脱去氨基,生成产物为环己烯和氨。     

新型P,N-配体的合成及其在钯催化碳-氮键偶联反应中的应用

以三苯基膦为母体骨架,设计合成了在苯环上连有环状仲胺取代基的五种新型P,N-配体(L1～L5),利用核磁共振谱(1H,13C,31p)、红外光谱、高分辨质谱和X射线单晶衍射等对配体进行了表征,并将它们应用于Pd催化的C-N键偶联反应中.结果表明,三(2-吗啉基苯基)膦(L5)与三(二亚苄基丙酮)二钯(Pd2(dba)3...     

Double-layer structure and mechanism of electrode reactions: I. Nitromethane reduction on mercury from aqueous solutions

Kinetic measurements of CH₃NO₂ electroreduction in aqueous solutions of pH values ranging from 1 to 9 were carried out with the polarographic technique under different experimental conditions. In particular, different concentrations of the supporting electrolytes NaClO₄ and NaCl, which are nonspecifically adsorbed at the potentials investigated, or else of the specifically adsorbed electrolyte KI, were employed to change the potential _d at the outer Helmholtz plane and/or the charge density q_i at the inner Helmholtz plane. The effects of these changes between pH 4 and 9 are consistent with a rate-determining protonation step $C{H}_{3}N{O}_2^{?}\stackrel{(+H^{+})}{\to }C{H}_{3}N{O}_{2}H$ taking place within the compact layer. As pH is gradually decreased from 4 to 1, double-layer effects are satisfactorily interpreted by assuming that the control of the overall electrode process passes from the above protonation step to the electron-transfer step CH₃NO₂+e→CH₃NO₂^?, again occurring within the compact layer.     

The Phosphorus Bond,or the Phosphorus-Centered Pnictogen Bond: The Covalently Bound Phosphorus Atom in Molecular Entities and Crystals as a Pnictogen Bond Donor

The phosphorus bond in chemical systems, which is an inter- or intramolecular noncovalent interaction, occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a covalently or coordinately bonded phosphorus atom in a molecular entity and a nucleophile in another, or the same, molecular entity. It is the second member of the family of pnictogen bonds, formed by the second member of the pnictogen family of the periodic table. In this overview, we provide the reader with a snapshot of the nature, and possible occurrences, of phosphorus-centered pnictogen bonding in illustrative chemical crystal systems drawn from the ICSD (Inorganic Crystal Structure Database) and CSD (Cambridge Structural Database) databases, some of which date back to the latter part of the last century. The illustrative systems discussed are expected to assist as a guide to researchers in rationalizing phosphorus-centered pnictogen bonding in the rational design of molecular complexes, crystals, and materials and their subsequent characterization.     

Electrostatics,the Chemical Bond and Molecular Stability

Electrostatic models of the chemical bond are based on the Virial Theorem and hold promise for providing a reliable and accurate method for predicting heats of formation of molecules and free radicals. The Principle of Alternating Polarity which states that those compounds are most stable in which atoms of opposite polarity are bonded is shown to be quantitatively described by electrostatic models. Current fixed partial-charge models account for ΔH of hydrocarbon molecules and radicals. With inclusion of polarization effects, whose energies are small, they also account for the dipole moments in hydrocarbons. A brief account is given of a more general model with significant polarization interaction which is under development and which appears to be able to account for both ΔH and dipole moments of polar molecules.     

Effect of Alkali Metals on the Strength of Oxygen–Catalyst Bond in Co-Containing Perovskites

Modification of the perovskite SrCoO₃ with alkali metal atoms has a considerable influence on the strength of the oxygen–catalyst bond and causes an increase in the weakly bonded oxygen in the modified samples. An approximate correlation has been established between the reactivity of the oxygen in the perovskite and its catalytic activity in the non-stationary condensation of methane to higher hydrocarbons.     

吡咯与一系列小分子之间的双氢键

采用密度泛函理论, 在B3LYP/6-311++G(d, p)水平上对以吡咯为质子供体的一系列双氢键体系进行了详细的研究. 采用AIM理论对双氢键体系进行了电子密度拓扑分析, 讨论了双氢键的成键特征和双氢键形成前后受体和供体H原子的积分净电荷、偶极矩、体积和能量的变化.     

Molecular Recognition in Anion Coordination Chemistry. Structure,Binding Constants and Receptor-Substrate Complementarity of a Series of Anion Cryptates of a Macrobicyclic Receptor Molecule

The crystal structures of four anion cryptates [X^? ? BT -6H⁺] formed by the protonated macrobicyclic receptor BT -6H⁺ with F^?, Cl^?, Br^? and N have been determined. They provide a homogeneous series of anion coordination patterns with the same ligand. The small F^?-ion is tetracoordinated, while Cl^? and Br^? are bound in an octahedron of H-bonds. The non-complementarity between these spherical anions and the ellipsoïdal cavity of BT -6H⁺ is reflected in ligand distortions. Structural complementarity is achieved for the linear triatomic substrate N, which is bound by two pyramidal arrays of three H-bonds, each interacting with a terminal N-atom of N. The formation constants of the complexes formed by BT -6H⁺ with a variety of anions (halides, N, NO, carboxylates, SO, HPO, AMP^2?, ADP^3?, ATP^4?, P₂O) have been determined. Very strong complexations are found, as well as marked electrostatic and structural effects on stability and selectivity; in particular the binding of F^?, Cl^?, Br^?, and N may be analyzed in terms of the crystal structure data. The cryptand BT -6H⁺ is a molecular receptor containing an ellipsoïdal recognition site for linear triatomic substrates of size compatible with the size of the molecular cacity. Further developments of various aspects of anion coordination chemistry are considered.     

系列双磷维生素B1离子盐化合物的合成、结构及分子构象

将Ni(ClO4)2和NH4PF6分别与硫胺素焦磷酸在甲醇体系中反应, 得到了两个新的离子盐型化合物[TPP·ClO4·H2O](1)和[TPP·PF6·CH3OH](2)(TPP为硫胺素焦磷酸酯). 通过元素分析、红外光谱及X射线衍射等方法对它们进行了表征. 结构分析表明, 它们属于离子型化合物, 而且硫胺素焦磷酸与高氯酸根, 六氟磷酸根形成了大量的氢键网络结构. 结合计算结果进一步分析了化合物的活性及电子结构特征.     

多肽中氢键强度的理论研究

用B3LYP/6-31G^*法优化了多肽分子的几何构型,计算了各个构型的电荷分布和氢键酸度,进而对多肽分子中的氢键强度进行了研究.结果表明,多肽分子中氢键的强度同时取决于形成氢键的H…O原子间距R和N-H…O之间的键角β;多肽分子倾向于形成R值小、β值大的大环氢键.3₁₀螺旋结构的多肽分子中的氢键具有协同效应,分子越大,分子中氢键越多,氢键的协同效应越强.     

Weakening and Leveling Effect of Solvent Polarity on Halogen Bond Strength of Diiodoperfluoroalkane with Halide

Weakening and leveling of the halogen bond (XB) between diiodoperfluoroalkane (DIPFA) and halide anions (X^?, X = Cl, Br and I) are imposed by solvent polarity. The solvents involved in this system are classified into three groups according to the acceptor number (AN) and solvent HB acidity (α) and were studied in detail. In non-competitive solvents, the strength of C–I···X^? XB is strongest, decreasing with electrostatic interaction in the order: C–I···Cl^? > C–I···Br^? > C–I···I^?. However, in weakly competitive solvents, the XB strength is largely weakened. Further, in strongly competitive solvents, the XB strength is leveled with no change occurring with X^?. This phenomenon can be attributed to the solvent effect. That is, the solvent can destabilize the DIPFA···X^? XB. This was confirmed by the experiment showing that the XB was destroyed as very small amounts of water was added into the CH₃CN solution of DIPFA and X^?.     

Effect of the Heterocyclic Ligand in Iron Porphyrinate Complex on the Strength of the Bond Between Iron and CO Molecule

The geometry and the electronic structure of iron porphyrinate complexes with various heterocyclic molecules in the fifth coordination position and a CO molecule in the sixth position were studied by density functional theory calculations. In the series of complexes with furan, imidazole, and pyrimidine, the bond between the Fe atom and CO is weakened due to the decrease in the overlap of the corresponding AOs.