二聚体C2H4-nFn···LiH (n=0, 1, 2)中π锂键的性质和弱方向性

采用二级微扰理论(MP2)量子化学研究方法, 对C₂H_4-nF_n···LiH (n=0, 1, 2)二聚体的结构和π锂键性质进行了分析. 结果表明氟原子的取代改变了乙烯分子的π电子云形状, 从而使二聚体体系中的π锂键发生偏移、伸长和弯曲. 通过与类似的π氢键体系C₂H_4-nF_n···HF (n=0, 1, 2)比较, 发现π锂键在二级弱相互作用的影响下, 发生了明显的弯曲, 表现出弱的方向性. 在CCSD(T)/6-311++G(3df, 3pd)理论水平下, 二聚体的相互作用能强弱顺序为: 33.85 kJ·mol^-1 (C₂H₄-LiH)>27.32 kJ·mol^-1 (C₂H₃F-LiH)>21.34 kJ·mol^-1 (cis-C₂H₂F₂-LiH)>20.25 kJ·mol^-1 (g-C₂H₂F₂-LiH), 说明氟取代削减了乙烯分子与LiH之间的相互作用.     

Copper-catalyzed synthesis of α-ketothioamides from ketones

In this paper, the conversion of acetophenone to α-ketothioamide was reported in the presence of CuI as the catalyst and S₈/DMF as the coupling partners. The presence of both KF and NaOH was found to be necessary to achieve the high yield of the product. Propiophenone and butyrophenone also reacted in the presence of phenylboronic acid as an additive. Willgerodt-Kindler products were not observed in these reactions.     

顺式效应的起源: 双取代乙烯衍生物的密度泛函理论研究

一般情况下双取代乙烯衍生物的反式构象要比顺式构象稳定. 但是例外也存在, 例如1,2-二氟乙烯和1,2-二氯乙烯. 这种双取代乙烯衍生物顺式构象的超常稳定性被称之为顺式效应. 该效应的起源和本质目前仍没有定论. 本文以12 个体系(XHC=CHY (X, Y=F, Cl, Br, CN, CH₃, C₂H₆, OCH₃))为例, 对顺式效应的有效性、起源和本质进行系统的密度泛函理论研究, 其中9个体系存在顺式效应, 另外3个为正常体系没有该效应. 采用一系列泛函和基组研究其有效性, 并运用四种分析手段, 如自然键轨道(NBO)、能量分量分析(EDA)、密度泛函活性理论(DFRT)和非共价相互作用(NCI)分析, 剖析该效应的起源和本质. 发现在顺式构象的两个取代基之间存在一种微弱的非共价相互吸引作用. 能量分析表明, 静电效应、立体效应等对顺式效应的存在都起着重要作用, 但是它们均不能单独用来解释顺式效应的起源. 也就是说顺式效应没有一个简单的起源, 它是多种作用合力的结果. 本文采用双变量解释得到比较合理的相关回归系数R²=0.86-0.87,较好地解释了顺式效应的本质和起源.     

CN and CC Bond Formations in the Thermal Reactions of "Bare" Ni(NH(2) )(+) with C(2) H(4) : Mechanistic Insight on the Metal-Mediated Hydroamination of an Unactivated Olefin

Strike! While pure ammonia is out of luck, Ni(NH(2) )(+) gets one strike after another at the "ethylene bowling championship". In fact, Ni(NH(2) )(+) is so effective that no pin, not even at the neighboring lane, is safe from it.     

分子间的非共价相互作用：σ-穴键和π-穴键

第四到第七主族元素以及惰性气体元素可以作为电子受体位点形成分子间吸引性的非共价键合作用。这些电子受体位点,即缺电子密度的位点,大多情况下具有正的分子表面静电势,可以将其分为2类。沿着σ共价键键轴延伸方向原子的外围中心具有正的分子表面静电势的区域称之为σ-穴。而垂直于分子σ-骨架平面具有正的分子表面静电势区域称之为π-穴。σ-穴和π-穴与富电性位点之间吸引性的相互作用分别称之为σ-穴键和π-穴键。σ-穴键倾向于180°,而π-穴键倾向于90°。按照元素周期表族的名称,σ-穴键又分为碳素键、氮素键、氧素键、卤键、惰素键等。可见流行的卤键只是σ-穴键的一个子集。π-穴键分类显得复杂些,可简单分为单原子和多原子π-穴键。     

MM3 parameterization for the B?N dative bond

A number of compounds that contain the B? N dative bond have been found to exhibit intriguing physiological activities. Although there is no proven mechanism for this activity, one hypothesis is that some form of borane transfer reaction occurs. In this scenario, the B? N dative bond within the small molecule, putative pharmacore breaks, and the borane forms a new dative bond with a Lewis base site on some critical protein. For this hypothesis to be investigated further from a computational perspective, an improved MM3 parameter set for tetravalent B? tetravalent N bonds has been developed and is reported here. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 913–922, 2001     

Transition‐metal‐catalyzed aminations and aziridinations of C?H and CC bonds with iminoiodinanes

Catalytic insertion or addition of a metal‐imido/nitrene species, generated from reaction of a transition‐metal catalyst with iminoiodanes, to C? H and C?C bonds offers a convenient and atom economical method for the synthesis of nitrogen‐containing compounds. Following this groundbreaking discovery during the second half of the last century, the field has received an immense amount of attention with a myriad of impressive metal‐mediated methods for the synthesis of amines and aziridines having been developed. This review will cover the significant progress made in improving the efficiency, versatility and stereocontrol of this important reaction. This will include the various iminoiodanes, their in situ formation, and metal catalysts that could be employed and new ligands, both chiral and non‐chiral, which have been designed, as well as the application of this functional group transformation to natural product synthesis and the preparation of bioactive compounds of current therapeutic interest. DOI 10.1002/tcr.201100018     

Lantern-type dinickel complexes: An exploration of possibilities for nickel–nickel bonding with bridging bidentate ligands

Many binuclear nickel complexes have Ni Ni distances suggesting Ni Ni covalent bonds, including lantern-type complexes with bridging bidentate ligands. This DFT study treats tetragonal, trigonal, and digonal lantern-type complexes with the formamidinate, guanidinate, and formate ligands, besides some others. Formal bond orders (ranging from zero to two) are assigned to all the Ni Ni bonds on the basis of MO occupancy considerations. A VB-based electron counting approach assigns plausible resonance structures to the dinickel cores. Model tetragonal complexes with the dimethylformamidinate and the dithioformate ligands have singlet ground states whose non-covalently bonded Ni Ni distances are close to those in their experimentally known counterparts. Trigonal dinickel complexes are unknown, but are predicted to have quartet ground states with Ni Ni bonds of order 0.5. The model digonal complexes are predicted to have triplet ground states, but the predicted Ni Ni bond lengths are longer than those found in their experimentally known counterparts. This could owe to inadequate treatment of electron correlation by DFT in these short Ni Ni bonds with their multiconfigurational character. All the Ni Ni bond distances here are categorized into ranges according to the Ni Ni bond orders of 0, 0.5, 1, 1.5, and 2, no Ni Ni bonds of order higher than two being identified. The Ni Ni bonds of given order in these lantern-type complexes are consistently shorter than the corresponding Ni Ni bonds in dinickel complexes having carbonyl ligands, attributable to the metal metal bond lengthening effect of CO ligands.     

Comparison of the Ability of N-Bases to Engage in Noncovalent Bonds

The lone pair of the N atom is a common electron donor in noncovalent bonds. Quantum calculations examine how various aspects of the base on which the N is located affect the strength and other properties of complexes formed with Lewis acids FH, FBr, F₂Se, and F₃As that respectively encompass hydrogen, halogen, chalcogen, and pnicogen bonds. In most cases the halogen bond is the strongest, followed in order by chalcogen, hydrogen, and pnicogen. The noncovalent bond strength increases in the sp<sp²<sp³ order of hybridization of N. Replacement of H substituents on the base by a methyl group or substituting N by C atom to which the base N is attached, strengthens the bond. The strongest bonds occur for trimethylamine and the weakest for N₂.     

Chemical structures from the analysis of domain-averaged fermi holes. Nature of the Mn-Mn bond in bis(pentacarbonylmanganese)

Because of conflicting and contradictory classification based on traditional AIM characteristics, the nature of the Mn-Mn bond has been and still is the subject of continuing discussions. To overcome the existing inconsistencies in the interpretation of the nature of this bond, the bonding in Mn2(CO)10 has been analyzed and discussed in terms of new recently proposed methodology known as the analysis of domain-averaged Fermi holes. It has been shown that this analysis is able to reconcile the conflicting conclusions of earlier AIM-based studies with traditional anticipations based on simple electron counting rules. According to Fermi hole analysis, the Mn-Mn bond has the character of the more or less ordinary covalent single sigma bond, but the analysis also brings clear evidence in favor of Mn . . . (CO) intramolecular interactions between the metal atom and the ligands bonded to the other metal atom. These interactions could be responsible for the observed decrease of electron density at the bond critical point detected in AIM studies.     

Synthesis and Properties of Phosphorylated and Silylated α-Mercaptocarbonyl Compounds

Abstract

Phosphorylation and silylation of α -mercaptooarbonyl compounds have been investigated. A novel type of 1.4 S-O migration trimethylsilyl and P(III) groups has been discovered. The thiophosphite-thiophosphonate rearrangement when exposed to oxygen as well as heterocyclization with the formation of 1,3,2-oxathiaphospholenes and 1,3,2-oxathiasilalenes were also found. Some regularities of these processes and the properties of heterocycles synthesized have also been brought out.     

Comments on chemical properties reported for diphenyl disulfide and its derivatives: The merit of the phenyl groups

The symmetrical 2,2′-disubstitued derivatives of diphenyl disulfide showing widely spanning rates of electrophilic attack of the HIV-1 nucleocapsid protein p7 zinc fingers have been rationalized, based on the lowest unoccupied molecular orbital (LUMO)-lowering approach, by the substituents' π-effects and the hydrogen bond stabilization effects. In the 2,2′-amide- and 4,4′-N-amide-substituted derivatives, the extent of LUMO lowering has been reduced by the destabilization of lone-pair bond orbital, lp(N), present on the nitrogen atom of N-amide. From the natural bond orbital viewpoint, hydrogen bond stabilization of LUMO is mainly governed by stabilization of the σ*_SS bond orbital.     

Red and blue shifted hydridic bonds

By performing MP2/aug‐cc‐pVTZ ab initio calculations for a large set of dimer systems possessing a R? H hydridic bond involved in diverse types of intermolecular interactions (dihydrogen bonds, hydride halogen bonds, hydride hydrogen bonds, and charge‐assisted hydride hydrogen bonds), we show that this is rather an elongation than a shortening that a hydride bond undergoes on interaction. Contrary to what might have been expected on the basis of studies in uniform electric field, this elongation is accompanied by a blue instead of red shift of the R? H stretching vibration frequency. We propose that the “additional” elongation of the R? H hydridic bond results from the significant charge outflow from the sigma bonding orbital of R? H that weakens this bond. The more standard red shift obtained for stronger complexes is explained by means of the Hermansson's formula and the particularly strong electric field produced by the H‐acceptor molecule. © 2014 Wiley Periodicals, Inc.     

Untersuchungen zur Carbeninsertion in Al–Al-, Ga–Ga- und In–In-Bindungen

Investigations on the Insertion of Carbenes into Al–Al, Ga–Ga, and In–In Bonds Tetrakis[bis(trimethylsilyl)methyl]dialane(4) 1 reacts with methylthiomethyl lithium LiCH₂SMe by the formation of lithium thiomethanolate LiSMe and the insertion of the remaining carbene CH₂ into its Al–Al single bond. A chelating Lewis acid is formed exhibiting a central R₂Al–CH₂–AlR₂ group with two coordinatively unsaturated Al atoms, which coordinate the thiomethanolate anion by Al–S bonds. The product (μ-methylene)(μ-thiomethanolato)bis{bis[bis(trimethylsilyl)methyl]aluminate} ( 4 ) was characterized by a crystal structure determination and has a strongly folded Al₂CS heterocycle in the molecular core. In contrast, the corresponding compounds with Ga–Ga or In–In bonds show on treatment with methylthiomethyl lithium a fragmentation, and the carbene intermediate could not be detected in both isolated products, which were identified as [R₂E(CH₂SMe)₂][Li(TMEDA)] (E = Ga: 5 ; E = In: 6 ) and LiCH(SiMe₃)₂ probably formed by a metal exchange reaction.