Nature of Alkali- and Coinage-Metal Bonds versus Hydrogen Bonds

We have quantum chemically studied the structure and nature of alkali- and coinage-metal bonds (M-bonds) versus that of hydrogen bonds between A−M and B⁻ in archetypal [A−M⋅⋅⋅B]⁻ model systems (A, B=F, Cl and M=H, Li, Na, Cu, Ag, Au), using relativistic density functional theory at ZORA-BP86-D3/TZ2P. We find that coinage-metal bonds are stronger than alkali-metal bonds which are stronger than the corresponding hydrogen bonds. Our main purpose is to understand how and why the structure, stability and nature of such bonds are affected if the monovalent central atom H of hydrogen bonds is replaced by an isoelectronic alkali- or coinage-metal atom. To this end, we have analyzed the bonds between A−M and B⁻ using the activation strain model, quantitative Kohn-Sham molecular orbital (MO) theory, energy decomposition analysis (EDA), and Voronoi deformation density (VDD) analysis of the charge distribution.     

非经典多重键

在难以形成经典多重键的重原子（第三周期以下）之间可以形成一种非经典多重键。由于构成双键的两部分（即两个分子片）的基态分别是单线态,这种电子结构导致非经典双键由两个配位键构成,非经典三键则是在此基础上再加上一个π键。这种多重键的强度和键级较经典多重键为低。与两个配位键的电子结构相对应,含有非经典多重键的分子具有反式弯曲的几何构型。     

Catalysis with Chalcogen Bonds

Herein, we introduce catalysts that operate with chalcogen bonds. Compared to conventional hydrogen bonds, chalcogen bonds are similar in strength but more directional and hydrophobic, thus ideal for precision catalysis in apolar solvents. For the transfer hydrogenation of quinolines and imines, rate enhancements well beyond a factor of 1000 are obtained with chalcogen bonds. Better activities with deeper σ holes and wider bite angles, chloride inhibition and correlation with computed anion binding energies are consistent with operational chalcogen bonds. Comparable to classics, such as 2,2′‐bipyrroles or 2,2′‐bipyridines, dithieno[3,2‐b;2′,3′‐d]thiophenes (DTTs), particularly their diimides, but also wide‐angle cyclopentadithiazole‐4‐ones are identified as privileged motifs to stabilize transition states in the focal point of the σ holes on their two co‐facial endocyclic sulfur atoms.     

Properties of Sulfur-Sulfur Bonds

SS bonds are extraordinarily flexible and have properties that are observed only on isolated occasions for other homonuclear bonds: the bond lengths very between 1.8 and 3.0Å, the bond angles between 90 and 180° and the dihedral angles between 0 and 180°; the bond energies amount to up to 430 kJ/mol. The SS stretching frequencies can appear over the range 177–820 cm^?1 and force constants of 1.4 to 6.3 mdyne/Å have been calculated. This variability is illustrated with examples containing isolated and cumulated SS bonds.     

Conversion of Triple Bonds into Single Bonds in a Domino Carbopalladation with Norbornene

A domino carbopalladation reaction of haloalkynes is presented. Remarkably, the four‐time carbopalladation process converts the carbon‐carbon triple bonds of haloalkynes stepwise into carbon–carbon double bonds, and finally to carbon‐carbon single bonds. Features of this reaction are that the carbon‐carbon double bonds of stable vinyl palladium intermediates are transformed into carbon‐carbon single bonds with the generation of unstable alkyl palladium intermediates. The subsequently formed π‐allylpalladium species are independently trapped by N ‐tosylhydrazones, boronic acids, and B₂pin₂ in a highly diastereoselective manner, delivering the corresponding polycyclic and twisted products with a bicyclo[3.2.1]oct‐2‐en‐3‐yl)tricyclo[3.2.1.0^2,4]octane core skeleton in moderate to good yields via C−C and C−B bond formations. Significantly, the dual roles of norbornenes, ring construction and ring expansion, and the identification of electron‐rich tri(2‐furyl)phosphine as the ligand are found to be critical for the success of these transformations.     

The Balance between Hydrogen Bonds,Halogen Bonds,and Chalcogen Bonds in the Crystal Structures of a Series of 1,3,4-Chalcogenadiazoles

In order to explore how specific atom-to-atom replacements change the electrostatic potentials on 1,3,4-chalcogenadiazole derivatives, and to deliberately alter the balance between intermolecular interactions, four target molecules were synthesized and characterized. DFT calculations indicated that the atom-to-atom substitution of Br with I, and S with Se enhanced the σ-hole potentials, thus increasing the structure directing ability of halogen bonds and chalcogen bonds as compared to intermolecular hydrogen bonding. The delicate balance between these intermolecular forces was further underlined by the formation of two polymorphs of 5-(4-iodophenyl)-1,3,4-thiadiazol-2-amine; Form I displayed all three interactions while Form II only showed hydrogen and chalcogen bonding. The results emphasize that the deliberate alterations of the electrostatic potential on polarizable atoms can cause specific and deliberate changes to the main synthons and subsequent assemblies in the structures of this family of compounds.     

Planar Complexes Containing Metal-Metal Bonds

Planar complexes, and particularly those of platinum, can form structures containing linear chains of heavy metal atoms with metal-metal distances as short as 3.1 Å. The bonding in these chains can be strengthened by partial oxidation, and the bond lengths can be reduced to 2.8 Å in this way. Model structures for the novel nonstoichiometric products, such as K₂[Pt(CN)₄]Cl_0·32 · 2.6 H₂O, are considered. The bonding is also discussed on the basis of a one-dimensional band model.     

Hydride‐Triel Bonds

In this article, we present the results of our comprehensive studies of 72 dimers of the type (X = Si, Ge; Y = B, Al, Ga; R^X = H, Cl, Me; R^Y = H, F, Cl, Me) and featuring hydride‐triel bonds (i.e., charge‐inverted hydrogen bonds). Influence of X and Y atoms as well as R^X and R^Y substituents on various properties of these dimers is investigated in detail. In particular the strength of the H⋯Y hydride‐triel bonds is paid a close attention and it is shown that hydride‐triel bonds can be strong enough to considerably determine structure and properties of molecular systems. In addition, properties of the investigated dimers are largely governed by the charge transfer from the Lewis base to the Lewis acid, which is particularly important if more bulky and polarizable R^Y and Y atoms are present in the molecule. Several excellent linear (R² close to 1) and exponential correlations between pairs of diverse parameters are presented. Few instances are discussed where somewhat unexpected bond paths exist between two atoms featuring partial negative charges (e.g., between hydride hydrogen and halogen and between lateral sides of two halogens) showing that in some cases a bond path prefers to link two closely spaced electron‐rich atoms instead of two atoms that are expected to form a bond. © 2018 Wiley Periodicals, Inc.     

基于钯催化的C—H选择性官能团化构建C—C键*

近几十年来,钯催化C—H键的选择性官能团化反应已成为有机合成中构建C—C键的重要策略,基本可以分为三类反应模式：C—H键与芳基或烷基卤化物（或拟卤化物）的交叉偶联反应、C—H键之间的交叉脱氢偶联反应、C—H键与金属有机化合物的交叉偶联反应。本文综述了该领域的最新研究进展,介绍了各类反应的特点、优势及在合成中的应用,提出了今后研究和发展的重点及方向。     

Noncovalent Bonds between Tetrel Atoms

The pairing of TFH₃ with a TH₂CH₃⁻ anion, where T represents tetrel atoms C, Si, Ge, Sn, Pb, results in a strong direct interaction between the two T atoms. The interaction energy is sensitive to the nature of the two T atoms but can be as large as 90 kcal/mol. The noncovalent bond strength rises quickly as the basic T atom of the anion becomes smaller, or as the Lewis acid T grows larger, although there is less sensitivity to the latter atom. The electrostatic component makes up some 55–70 % of the total attraction energy. This term is well accounted for by simple combination of the maximum and minimum values of the molecular electrostatic potential of the Lewis acid and base units, respectively. The complexation induces a rearrangement in the TFH₃ molecule from tetrahedral to trigonal pyramidal. The associated deformation energy reduces the exothermicity of the complexation reaction. Electron density shift patterns reveal a density loss on the basic T atom, along with accompanying increases on the acidic T and its attached F atom.     

Molecular Versus Supramolecular Chemistry: The Rotational Barriers About Covalent Bonds and Hydrogen Bonds

The barrier about the C—C bond in 1,1,1-trifluoroethane amounts to 13–14 kJ mol-1 while that about the hydrogen bond in the trifluoromethane/ammonia complex is almost null.     

New Cyclotriphosphazenes with P-CAr Bonds

Abstract

We describe some new cyclotriphosphazenes in which the phosphorus substituents are either free rotating aromatic or heteroaromatic groups, or rigid spirobiaryl units.     

Lithium Bonds in Lithium Batteries

Lithium bonds are analogous to hydrogen bonds and are therefore expected to exhibit similar characteristics and functions. Additionally, the metallic nature and large atomic radius of Li bestow the Li bond with special features. As one of the most important applications of the element, Li batteries afford emerging opportunities for the exploration of Li bond chemistry. Herein, the historical development and concept of the Li bond are reviewed, in addition to the application of Li bonds in Li batteries. In this way, a comprehensive understanding of the Li bond in Li batteries and an outlook on its future developments is presented.     

Strength of Intramolecular Hydrogen Bonds

The concept of resonance-assisted hydrogen bonds(RAHBs)highlights the synergistic interplay between theπ-resonance and hydrogen bonding interactions.This concept has been well-accepted in academia and is widely used in practice.However,it has been argued that the seemingly enhanced intramolecular hydrogen bonding(IMHB)in unsaturated compounds may simply be a result of the constraints imposed by theσ-skeleton framework.Thus,it is crucial to estimate the strength of IMHBs.In this work,we used two approaches to probe the resonance effect and estimate the strength of the IMHBs in the two exemplary cases of the enol forms of acetylacetone and o-hydroxyacetophenone.One approach is the block-localized wavefunction(BLW)method,which is a variant of the ab initio valence bond(VB)theory.Using this approach,it is possible to derive the geometries and energetics with resonance shut down.The other approach is Edmiston’s truncated localized molecular orbital(TLMO)technique,which monitors the energy changes by removing the delocalization tails from localized molecular orbitals.The integrated BLW and TLMO studies confirmed that the hydrogen bonding in these two molecules is indeed enhanced byπ-resonance,and that this enhancement is not a result ofσconstraints.     

晶体化学中的次级键

应用现代实验技术精确测定分子和晶体的微观结构是 2 0世纪自然科学的一项伟大成就。主要基于晶体结构数据归纳出来的 4套半径数据 ,即离子半径、共价半径、金属原子半径和范德华半径构成了结构化学的支柱。人们利用其各自具有的恒定性和加和性研究物质的结构以及结构与性能的关系 ,已经取得了丰硕的成果。　　离子键、共价键和金属键是化学键的极限类型。不同化学键型之间的过渡所形成的相对于极限键型的偏离被称为键型的变异 ,但是化学键与范德华引力是原子间作用力的不同层次。除后者无须电子云重迭因而没有方向性和饱和性外 ,其作用能要…     

原子间的另一种作用力——氢键

从氢键定义的延伸、键能大小及其共价性质的表现，认为氢键内容的发展已经可以将之称为"原子间的另一种作用力"。在此基础上，尝试推动氢键教学内容的改革，这样不但可以丰富基础无机化学中"氢键"的内容，而且可以有效增进学生从基础课教学提高科学研究的意识。     

Understanding Regium Bonds and their Competition with Hydrogen Bonds in Au2:HX Complexes

A theoretical study of the regium and hydrogen bonds (RB and HB, respectively) in Au₂:HX complexes has been carried out by means of CCSD(T) calculations. The theoretical study shows as overall outcome that in all cases the complexes exhibiting RB are more stable that those with HB. The binding energies for RB complexes range between −24 and −180 kJ ⋅ mol^−1, whereas those of the HB complexes are between −6 and −19 kJ ⋅ mol⁻¹. DFT-SAPT also indicated that HB complexes are governed by electrostatics, but RB complexes present larger contribution of the induction term to the total attractive forces. ¹⁹⁷Au chemical shifts have been calculated using the relativistic ZORA Hamiltonian.