Theoretical Studies on the Dihydrogen Bonding Between Shortchain Hydrocarbon and Magnesium Hydride

The C--H…H dihydrogen-bonded complexes of methane, ethylene, acetylene, and their derivatives with magnesium hydride were systematically investigated at MP2/aug-cc-PVTZ level. The results confirm that the strength of dihydrogen bonding increases in the following order of proton donors： C（sp3）-H〈C（sp2）-H〈C（sp）-H and chlorine substituents enhance the C-H…H interaction. In the majority of the complexes with a cyclic structure, the Mg-H proton-accepting bond is more sensitive to the surroundings than C-H proton-donating bond. The nature of the electrostatic interaction in these C-H…H dihydrogen bonds was also unveiled by means of the atoms in mo- lecules（AIM） analysis. The natural bond orbital（NBO） analysis suggests that the charge transfer in the cyclic com- plexes is characteristic of dual-channel. The direction of the net charge transfer in the cyclic complexes is contrary to that previously found in dihydrogen bonded systems.     

Transformations of N-arylpropiolamides to indoline-2,3-diones and acids via C≡C triple bond oxidative cleavage and C(sp^2)–H functionalization

A new palladium-catalyzed oxidative conversion of N-arylpropiolamides and H2O to various indoline-2,3-diones and acids through the C≡C triple bond cleavage and C(sp2)–H functionalization is described,which is promoted by a cooperative action of catalytic CuBr2,2,2,6,6-tetramethyl-1-piperidinyloxy(TEMPO)and O2.The method provides a practical tool for transformations of alkynes by means of a C–H functionalization strategy,which enables the formation of one C–C bond and multiple C–O bonds in a single reaction with high substrates compatibility and excellent functional group tolerance.     

Theoretical study of the N—H···O red-shifted andblue-shifted hydrogen bonds

Theoretical calculations are performed to study the nature of the hydrogen bonds in complexes HCHO···HNO, HCOOH···HNO, HCHO···NH3, HCOOH···NH3, HCHO···NH2F and HCOOH···NH2F. The geomet- ric structures and vibrational frequencies of these six complexes at the MP2/6-31 G(d,p), MP2/6-311 G(d,p), B3LYP/6-31 G(d,p) and B3LYP/6-311 G(d,p) levels are calculated by standard and counterpoise-corrected methods, respectively. The results indicate that in complexes HCHO···HNO and HCOOH···HNO the N—H bond is strongly contracted and N—H···O blue-shifted hydrogen bonds are observed. While in complexes HCHO···NH3, HCOOH···NH3, HCHO···NH2F and HCOOH···NH2F, the N—H bond is elongated and N—H···O red-shifted hydrogen bonds are found. From the natural bond orbital analysis it can be seen that the X—H bond length in the X—H···Y hydrogen bond is controlled by a balance of four main factors in the opposite directions: hyperconjugation, electron density redistribu- tion, rehybridization and structural reorganization. Among them hyperconjugation has the effect of elongating the X—H bond, and the other three factors belong to the bond shortening effects. In complexes HCHO···HNO and HCOOH···HNO, the shortening effects dominate which lead to the blue shift of the N—H stretching frequencies. In complexes HCHO···NH3, HCOOH···NH3, HCHO···NH2F and HCOOH···NH2F where elongating effects are dominant, the N—H···O hydrogen bonds are red-shifted.     

An MP2 study on pre-reactive complexes (CH_2)_2O … XY (X,Y = H,F,Cl,Br,I)

The structures, energies, atomic chaiges and IR spectra of complexes (CH2)2O…XY (X, Y = H, F, Cl, Br, and I) have been examined by means of ab initio molecular orbital theory at the second-order level of Moller-Plesset perturbation correction. It is found that the hydrogen bond O…H-X is non-linear. The attraction between X and the H atoms in oxirane ring causes O…H-X bond bending. The hydrogen bond slighdy weakens the bond strength of C-O, and leads the bending and stretching mode of IR to shift to the red. The calculation results show that there is no evidence of a significant extent of proton transfer to give (CH2)2OH …X- in the isolated complexes.     

Unraveling weak interactions in aniline-pyrrole dimer clusters

Weak intermolecular interactions in aniline-pyrrole dimer clusters have been studied by the dispersion-corrected density functional theory(DFT) calculations. Two distinct types of hydrogen bonds are demonstrated with optimized geometric structures and largest interaction energy moduli. Comprehensive spectroscopic analysis is also addressed revealing the orientation-dependent interactions by noting the altered red-shifts of the infrared and Raman activities. Then we employ natural bond orbital(NBO)analysis and atom in molecules(AIM) theory to have determined the origin and relative energetic contributions of the weak interactions in these systems. NBO and AIM calculations confirm the V-shaped dimer cluster is dominated by N.H···N and C.H···π hydrogen bonds, while the J-aggregated isomer is stabilized by N.H···π, n→π* and weak π···π* stacking interactions.The noncovalent interactions are also demonstrated via energy decomposition analysis associated with electrostatic and dispersion contributions.     

Theoretical Study on Dihydrogen Bonds of NH3BH3 with Several Small Molecules

The dihydrogen bonds B-H...H-X （X= the complexes of NH3BH3 with HF, HCl, F, Cl, Br, C, O, N） in the dimer （NH3BH3）2 and HBr, H2CO, H20, and CH3OH were theoretically studied. The results show that formation of the dihydrogen bond leads to elongation and stretch frequency red shift of the BH and XH bonds, except that in the H2CO system, the CH bond blue shifts. For （NH3BH3）2 and the complexes of the halogenides, red shifts of the XH bonds are caused by the intermolecular hyperconjugation σ（BH）→σ^＊ （XH）. For the system of H2CO, a blue shift of the CH bond is caused by a decrease of the intramolecular hyperconjugation n（O→σ^＊ （CH）. In the other two systems, the red shift of OH bond is a secondary effect of the stronger traditional red-shifted H-bonds N-H... O. In all these systems, red shifts of the BH bonds are caused by two factors： negative repolarization and negative rehybridization of the BH bond, and decrease of occupancy on σ（BH） caused by the intermolecular hyperconjugation σ（BH）→σ^＊ （XH）.     

Theoretical Studies on the Hydrogen Bonds of Different Position Action Mechanisms of Thymine with Uracil

In this research, the hydrogen bonds Y···H-X(X = C, N; Y = N, O) of thymine and uracil have been theoretically studied. The results show that hydrogen bond leads to bond length elongation and stretches the frequency red-shift of N-H···Y. Meanwhile, the C-H···O bonds shorten and stretch the frequency blue-shift. They all belong to traditional hydrogen bonds. The intermolecular charge transfer caused by the intermolecular hyperconjugation ρ*(N–H) →n(Y) and intramolecular charge redistribution by intramolecular hyperconjugation ρ(C-H)→ρ*(C-N) play important roles in the formation of hydrogen bonds. According to the judgment standards proposed by Bader and Popelier, these hydrogen bonds have typical electron density topological properties. Electrostatic surface potential(ESP) is a useful physicochemical property of a molecule that provides insights into inter- and intramolecular associations, as well as the prediction of likely sites of electrophilic and nucleophilic metabolic attack.     

Catalytic transformation of cellulose and its derived carbohydrates into chemicals involving C–C bond cleavage

The catalytic transformation of cellulose, the major component of abundant and renewable lignocellulosic biomass, into building-block chemicals is a key to establishing sustainable chemical processes. Cellulose is a polymer of glucose and a lot research effort has been devoted to the conversion of cellulose to six-carbon platform compounds such as glucose and glucose derivatives through C–O bond activation. There also exist considerable studies on the catalytic cleavage of C–C bonds in biomass for the production of high-value chemicals, in particular polyols and organic acids such as ethylene glycol and lactic acid. This review article highlights recent advances in the development of new catalytic systems and new strategies for the selective cleavage of C–C bonds in cellulose and its derived carbohydrates under inert, reductive and oxidative atmospheres to produce C1–C5polyols and organic acids. The key factors that influence the catalytic performance will be clarified to provide insights for the design of more efficient catalysts for the transformation of cellulose with precise cleavage of C–C bonds to high-value chemicals. The reaction mechanisms will also be discussed to understand deeply how the selective cleavage of C–C bonds can be achieved in biomass.     

Copper-catalyzed enantioselective cyanation of benzylic C–H bonds via radical relay

正Direct methods that enable stereoselective functionalization of C(sp~3)–H bonds could facilitate efficient preparation of therapeutics and agrochemicals,and shall have a major effect on the discovery and development of new pharmaceuticals.Although the transformations through C(sp~2)–H bond cleavage have been significantly developed in the past decades,the direct C(sp~3)–H functionalization,especially the asymmetric transformation is still a big challenge.Demon-     

A new class of ion-ion interaction: Z-bond

The hydrogen-bond interactions in ionic liquids have been simply described by the conventional hydrogen-bond model of A–H···B. Coupling with the strong electrostatic force, however, hydrogen bond between the cation and anion shows particular features in the geometric, energetic, electronic, and dynamic aspects, which is inherently different from that of the conventional hydrogen bond. A general model could be expressed as +[A–H···B]-, in which A and B represent heavy atoms and "+" and "–" represent the charges of the cation containing A atom and anion containing B atom, respectively. Because the structure shows a "zig-zag" motif, this coupling interaction is defined here as the Z-bond. The new model could be generally used to describe the interactions in ionic liquids, as well as bio-systems involved in ions, ionic reaction, and ionic materials.     

STUDY ON ELECTRONIC STRUCTURE AND BONDING OF CLUSTER COMPOUND Sc_7Cl_(10)C_2

<正> The electronic structure and bonding of the cluster compound Sc7Cl10C2 have been studied by INDO method. In contract to the weak interaction between metal-metal in the compound Gd10Cl18C4, the bonding between metal atoms (Sc-Sc) in Sc7Cl10C2 is rather strong. The contribution of the orbitals 4s and 4p is larger than that of 3d to the Sc-Sc bond. In the cluster compound, besides Sc-Sc bonding, there are Sc -C and Sc -Cl bonds. The contribution of 3d is larger than that of 4s and 4p to the bond Sc-C. The contribution of 3d is slightly less than that of 4p and 4s to the bond Sc-Cl. Among the three kinds of bonds, the Sc-Cl bond is the weakest, the bond order of the Sc-Sc is close to that of the Sc-C.     

Single Crystal of Lanthanum Hydroxide La(OH)3: Controlled Synthesis by High Pressure Flux Method and Its Growth Mechanism

High pressure synthesis of solid material tends to increase the density,coordination number,symmetry of material and shorten bond length.The solid synthesized at a high pressure and decompressed to ambient pressure often exhibits a metastable "stretched" state,within the high pressure stability field.The crystal grown at a high pressure is of great importance with the development of high pressure technology.Crystal growth is an important factor in the material synthesis.And many methods including gas,solid and solution methods have been used to obtain various single crystals[1].Especially,flux method is an important method for crystal growth,where the components of the desired substance dissolved in a solvent(flux) grow in the process of deposit.Its advantage is that the crystal growth displays natural facets and the disadvantage is that the crystals are relatively small.Up to date,some solid materials have been successfully synthesized by high pressure flux method[2-7].     

Trimer formation of 6-methyl-1,3,5-triazine-2,4-diamine in salt with organic and inorganic acids:analysis of supramolecular architecture

Although the numbers of co-crystals,salts,polymorphs,hydrates,and solvates are growing steadily,trimers that contain both inorganic and organic acids are still very rare in the Cambridge Structural Database(CSD).When 3,5-dihydroxybenzoic acid was crystallized readily with 6-methyl-1,3,5-triazine-2,4-diamine in a 4:3 ratio of ethanol and water by adding a few drops of nitric acid upon slow evaporation in ambient conditions,6-methyl-1,3,5-triazine-2,4-diamine and 3,5-dihydroxybenzoic acid with the nitric acid form of 1:1:1 an inorganic-organic salt formulated as[(C4H8N5+)·(NO3-)·(C7H6O4)].The supramolecular architecture,which is quite elegant and simple,appeared as stacking of a 3D network in adduct.Proton transfer from the HNO3to 6-methyl-1,3,5-triazine-2,4-diamine N acceptor(triazine N)occurred in the organic salt and led to the ionic heterosynthon in the structure.Cooperation among the–COOH,–OH,NO3–,and–NH–functional groups for the observed hydrogen bond synthon was examined in the structure.In adduct,recognition among the constituents is established through N–H···O,O–H···N,and O–H···O hydrogen bonds.The agomelatine molecules are linked through the intermolecular hydrogen bonding interactions(O–H···O)to form a 1D chain.In addition,the nitric acid anions and base cations act as donors and acceptors of hydrogen bonds and interlink,almost to co-planarity,the hydrogen-bonded chains through interchain N–H···O,O–H···N,as well as O–H···O interactions into a 2D sheet structure.Persistent N–H···O interactions were found to play an important role in the formation of the final 3D array.The salt was characterized by elemental analysis,IR,thermogravimetric analysis,and singlecrystal X-ray diffraction,to better understand how intermolecular interactions influence its supramolecular assembly.     

Insights into the Decomposition and Polymerization of Cage Energetic Crystal Octanitrocubane under High Pressure: a DFT-D Study

Dispersion-corrected DFT calculations have been performed to study the crystal structure, initial decomposition mechanism, polymerization mechanism, electronic structure and absorption properties of the most powerful CHNO energetic compound octanitrocubane(ONC) under hydrostatic pressure of 0~200 GPa. Our results show that the lattice parameter c is sensitive to van der Waals interactions and the structure is the stiffest in the a direction. ONC decomposes by the breaking of N–O bond in nitro group at 195 GPa. At 200 GPa, ONC decomposes through the breaking of N–O bond in nitro group and polymerizes through the forming of a new C–O covalent bond between a carbon atom in the cage skeleton and one oxygen atom of nitro group in another ONC molecule. ONC becomes more and more sensitive under high pressure and transforms into a metallic phase in the pressure range of 175~200 GPa. ONC also has higher optical activity and wider absorption range under compression.     

Palladium-catalyzed hydrosilylation of ynones to access silicon-stereogenic silylenones by stereospecific aromatic interaction-assisted Si–H activation

Hydrosilylation is one of the most important reactions in synthetic chemistry and ranks as a fundamental method to access organosilicon compounds in industrial and academic processes. However, the enantioselective construction of chiral-at-silicon compounds via catalytic asymmetric hydrosilylation remained limited and difficult. Here we report a highly enantioselective hydrosilylation of ynones, a type of carbonyl-activated alkynes, using a palladium catalyst with a chiral binaphthyl phosphoramidite ligand. The stereospecific hydrosilylation of ynones affords a series of silicon-stereogenic silylenones with up to 94% yield, 20:1 regioselectivity and 98:2 enantioselectivity. The density functional theory(DFT) calculations were conducted to elucidate the reaction mechanism and origin of high degree of stereoselectivity, in which the powerful potential of aromatic interaction in this reaction is highlighted by the multiple C–H-π interaction and aromatic cavity-oriented enantioselectivitydetermining step during desymmetric functionalization of Si–H bond.     

Unactivated C(sp3)–H functionalization via vinyl cations

Direct functionalization of inert C(sp³)–H bonds is a topic of immense contemporary interest and exceptional value in organic synthesis.The recent research has established a novel and practical protocol which features the engagement of vinyl cation species to functionalize C(sp³)–H bonds.The discussion of the topic is arranged by the strategies to generate the reactive intermediates,including ionization of vinyl triflates,addition of electrophiles to alkynes,tandem cyclization of enynes or diynes,and decomposition ofβ-hydroxy-α-diazo ketones.This review closes with a personal perspective on the dynamic research area of unactivated C(sp³)–H functionalization via vinyl cations.Hopefully,it will provide timely illumination and beneficial guidance for organic chemists who are interested in this area.Meanwhile continued development of the field is strongly anticipated in the future.     

Ratiometric recognition of humidity by a europium-organic framework equipped with quasi-open metal site

Open metal site(OMS) seated in a luminescent lanthanide(Ln) metal center offers an opportunity for rationally tuning the spectroscopic behavior of lanthanide-organic frameworks aiming for a wide range of sensing applications. However, given the spherical nature of common coordination geometries of trivalent lanthanides and the generally strong Ln–O bonds, the lanthanide based OMS is rarely reported and difficult to be functionalized. We report here a unique europium-organic framework containing abundant quasi-OMS that is protected by an abnormal weak Eu–O bond. These quasi-OMSs offer reversible direct binding sites for water molecules probed by X-ray crystallography, leading to sensitive, visible, and ratiometric luminescent sensing toward humidity and water content in organic solvents. The specific recognition of water based on quasi-luminescentOMSs gives rise to a superior water detection limit down to 0.0003% v/v, which is one order of magnitude lower than that of Karl Fischer method.     

Regioselective introduction of vinyl trifluoromethylthioether to remote unactivated C(sp~3)–H bonds via radical translocation cascade

Described herein is an efficient protocol for the regioselective introduction of a vinyl trifluoromethylthioether to remote unactivated C(sp~3)–H bonds. The cascade process involves the vinyl radical-mediated 1,5-hydrogen atom transfer(HAT) and remote vinyl migration. During the transformation, inert C–H and C–C bonds are consecutively cleaved under mild conditions.The reaction features good functional group tolerance, broad substrate scope, and high regio-/stereo-selectivity.     

DFT Study on the Germanium Ion Activated C–H Bond in Methane

Thermal reactions of methane with the main group metal cations Ge~+,GeO~+,GeOH~+ and OGeOH~+ were investigated by state-of-the-art quantum chemical calculations.For GeO~+/CH_4,a H atom in CH_4 abstracted by the O atom in GeO~+ to form GeOH~+ and CH_3˙constitutes the channel mainly.The barrier-free process,combined with a large exothermicity,suggested a fast and efficient reaction in agreement with the experiment.For OGeOH~+ and CH_4,the intermediates and products of the most favorable path were below the reactant asymptote,and the reaction was easy to take place,while for Ge~+ and GeOH~+,the activation of C–H bond in methane was hard to happen under ambient temperature.The results showed,in contrast to the inertness of Ge~+ and Ge OH~+,the GeO~+ and OGeOH~+ can activate the H_3C–H bond.The NBO natural charge and molecular electrostatic potential were used to analyze the four main group metal germanium constructions.The phenomenon suggested that ligands affect the electronic character and tune the chemical features of metal germanium center.     

Spectroscopic Studies of a Three-dimensional,Five-coordinated Copper(Ⅱ） Complex via Hydrogen Bonds:[Cu(PPD)(H2O)2](H2PDA=Pyridine-2,6-dicarboxylic Acid)

A new copper(Ⅱ） complex[Cu(PDA)(H2O)2] was synthesized and its structure was determined.Cu(Ⅱ）is five-coordinated in a tetragonal pyramid geometry.The two coordinating water molecules are different and the two Cu-O bond lengths differ by nearly 0.02nm.The whole crystal is linked to form a three-dimensional network by means of hydrogen bonds.The X-band ESR spectrum shows three different g tensors with a well-resolved hyperfine structure in the gz signal,giving the ESR parameters gx=2.05,gy=2.065 and gz=2.29.The covalency of the coordinate bonds and the deviation from tetragonal pyramid geometry for the complex are discussed based on the ESR spectra.