Palladium-Catalyzed Formal [4＋2] Cycloaddition of Benzoic and Acrylic Acids with 1,3-Dienes via C-H Bond Activation： Efficient Access to 3,4-Dihydroisocoumarin and 5,6-Dihydrocoumalins

We report a palladium-catalyzed formal intermolecular [4＋2] cycloaddition of benzoic and acrylic acids with 1,3-dienes including the stock chemicals 1,3-butadiene and isoprene leading to synthetically useful 3,4-dihydroisocoumarins and 5,6-dihydrocoumalins. Stepwise C-H bond cleavage and annulation are likely involved in the reaction pathway. The synthetic potential of the methodology was demonstrated by two short derivatizations and total synthesis of natural product Clausamine B.

Direct C-H Bond Activation of Benzoxazole and Benzothiazole with Aryl Bromides Catalyzed by Palladium（Ⅱ）-N-heterocyclic Carbene Complexes

Herein, we report that a series of novel palladium（II）-NHC complexes （NHC=N-heterocyclic carbene） were synthesized. The structures of all novel complexes were characterized by ^1H NMR, ^13C NMR, FT-IR spectroscopy and elemental analysis techniques. These palladium（ll）-NHC complexes were tested as efficient catalysts in the direct C-H bond activation of benzoxazole and benzothiazole with aryl bromides in the presence of 1 mol% catalyst loading at 150 ℃ for 4 h. Under the given conditions, various aryl bromides were successfully applied as the arylating reagents to achieve the 2-arylbenzoxazoles and 2-arylbenzothiazoles in acceptable to high yields.

Palladium-catalyzed late-stage mono-aroylation of the fully substituted pyrazoles via aromatic C-H bond activation

The palladium-catalyzed late-stage aroylation of 4-methyl-1,5-diaryl-lH-pyrazole-3-carboxylates has been developed via direct and exclusive mono-Csp^2-H bond activation with broad substrate scope and good functional group tolerance. A dual-core dimeric palladacycle is confirmed by X-ray single crystal crystallography, and probably serves as an active species in the catalytic cycle.

Recent advances in the diversification of chromones and flavones by direct C-H bond activation or functionalization

Chromone and flavone are both central backbones of natural products and clinical medicines.Synthesis of diversely functionalized chromones and flavones constitutes significant research contents of the modern synthetic science because abundant molecular libraries of such types are crucial in providing candidate compounds for the discovery of new pharmaceuticals and functional materials.The direct C—H bond activation or functionalization on these heterocyclic backbones provides highly powerful tools for the rapid accesses to densely functionalized chromone and flavone derivatives.Considering the importance of the functionalized chromone and flavone compounds as well as the notable advances in the synthesis of such products by direct C—H activation or functionalization,we review herein the research advances in the C—H bond activation and functionalization reactions of chro mone and flavones,in hope of showing the current states and promise of the research domain.

Photocatalytic C-H Bonds Activation:Ambient Carbonylation of Cyclohexane by Co(acac)_2 Under Ultraviolet Irradiation

A high turnover number was achieved in the photocatalytic carbonylation of C - H bonds of cyclohexane catalyzed by Co (acac)2 under ambient conditions (1 atm,25℃) to give mainly cyclohexanecarboxaldehyde.

Catalytic Benzylation Reactions: From C-H Bond Activation to C-N Bond Activation

Transition-metal mediated activation of inert chemical bonds is an ongoing topic in homogeneous catalysis.In view of the abundance and accessibility of alkylarenes and benzylamines,the use of them as benzyl source in catalytic benzylation reactions via benzylic C-H and C-N bond activation is highly desirable.Indeed,compared with the traditional approaches with benzyl halide as the substrates,benzylation reactions via C-H and C-N bond cleavage provide more efficient,atom-economic strategies to access myriads of synthetically important molecules.In this account,our group's efforts on catalytic benzylation reactions via directed C-H activation,nondirected C-H activation and C-N bond activation are summarized.

Synthesizing active and durable cubic ceria catalysts(<6 nm)for fast dehydrogenation of bio-polyols to carboxylic acids coproducing green H_(2)

Dehydrogenation is considered as one of the most important industrial applications for renewable energy.Cubic ceria-based catalysts are known to display promising dehydrogenation performances in this area.Large particle size(>20 nm)and less surface defects,however,hinder further application of ceria materials.Herein,an alternative strategy involving lactic acid(LA)assisted hydrothermal method was developed to synthesize active,selective and durable cubic ceria of<6 nm for dehydrogenation reactions.Detailed studies of growth mechanism revealed that,the carboxyl and hydroxyl groups in LA molecule synergistically manipulate the morphological evolution of ceria precursors.Carboxyl groups determine the cubic shape and particle size,while hydroxyl groups promote compositional transformation of ceria precursors into CeO_(2) phases.Moreover,enhanced oxygen vacancies(Vo)on the surface of CeO_(2) were obtained owing to continuous removal of O species under reductive atmosphere.Cubic CeO_(2) catalysts synthesized by the LA-assisted method,immobilized with bimetallic PtCo clusters,exhibit a record high activity(TOF:29,241 h^(-1))and Vo-dependent synergism for dehydrogenation of bio-derived polyols at 200℃.We also found that quenching Vo defects at air atmosphere causes activity loss of PtCo/CeO_(2) catalysts.To regenerate Vo defects,a simple strategy was developed by irradiating deactivated catalysts using hernia lamp.The outcome of this work will provide new insights into manufacturing durable catalyst materials for aqueous phase dehydrogenation applications.

Competition between C-C and C-H Activation in Reactions of Neutral Nickel Atom with Cycloalkanes （n = 3-7）

A theoretical investigation of the reaction mechanisms for C-H and C-C bond activation processes in the reaction of Ni with cycloalkanes C,,H2. （n = 3-7） is carried out. For the Ni ＋ CnH2, （n = 3, 4） reactions, the major and minor reaction channels involve C-C and C-H bond activations, respectively, whereas Ni atom prefers the attacking of C-H bond over the C-C bond in CnH2n （n = 5=7）. The results are in good agreement with the experimental study. In all cases, intermediates and transition states along the reaction paths of interest are characterized, It is found that both the C-H and C-C bond activation processes are proposed to proceed in a one-step manner via one transition state. The overall C-H and C-C bond activation processes are exothermic and involve low energy barriers, thus transition metal atom Ni is a good mediator for the activity of cycloalkanes CnH2n （n = 3 -7）.

分子筛限域单位点钴体系催化芳香族化合物C-H键自调节高效氧化

通过芳香族化合物的碳-氢键活化与选择氧化,可以将廉价芳香烃类原料转化为高附加值含氧产品,因此,该反应在基础研究和工业生产中均受到广泛关注.传统的苯乙酮生产工艺存在毒性底物使用、催化剂回收困难、反应条件苛刻以及产物收率低等问题.通过大量的研究探索,科研人员进一步改进其生产工艺,利用环烷酸钴作为均相催化剂,实现了无溶剂条件下分子氧直接选择氧化乙苯生成苯乙酮.相比均相催化,多相催化在催化剂回收和产物分离方面具有优势,更适合工业化生产.因此,开发用于乙苯选择氧化制苯乙酮的高效稳定多相催化体系非常重要,但具有较大挑战.本文采用原位配体保护的水热合成法将钴配合物(钴-二乙烯三胺)封装在Y型分子筛中,并经进一步焙烧去除配体成功制得Co@Y分子筛催化剂.在无溶剂、无添加剂的条件下,单位点Co作为Co@Y分子筛催化剂的活性位点可催化乙苯选择氧化生成苯乙酮.X射线粉末衍射、透射电镜、紫外可见光吸收光谱和固体核磁共振谱等结果表明,该单位点Co(Co^(2+))通过与骨架氧原子作用稳定限域在Y型分子筛中.为明确Co@Y分子筛催化剂中单位点Co在乙苯氧化反应中所起的重要作用,本文还对比了不同后合成方法所制备的Y分子筛(Co/Y,Co-Y)催化剂及工业环烷酸钴催化剂的催化性能.结果表明,在相同反应条件下,Co@Y分子筛催化剂表现出最高的催化性能,也说明在乙苯氧化反应过程中Co@Y分子筛催化剂的单位点Co有别于上述其他催化剂的活性位点.此外,在Co@Y催化剂热过滤实验中未检测出Co物种浸出,表明Co@Y分子筛催化乙苯氧化反应为多相催化过程,并且在多次循环测试后,Co@Y催化剂结构和反应活性均未发生明显变化.这两项实验均表明Co@Y催化剂具有高稳定性.值得注意的是,在乙苯氧化反应过程中观察到自加速现象,为此进行了对比实验(添加苯甲醛或1-苯乙醇的对比实验)和反应动力学分析.结果表明,痕量苯甲醛或1-苯乙醇的加入会显著改变Co@Y催化剂在乙苯氧化反应中的催化行为,痕量苯甲醛的加入可将反应表观活化能从69.7降至53.7 kJ/mol.本文也通过第一性原理密度泛函理论(DFT)计算系统研究了Co@Y分子筛催化剂单位点Co处乙苯选择氧化反应机理及反应过程中自加速现象产生的原因.DFT计算结果结合上述对比实验和反应动力学分析结果表明,加入痕量苯甲醛或者1-苯乙醇后部分乙苯会直接氧化生成苯乙酮,而非通过乙苯→1-苯乙醇→苯乙酮的途径生成苯乙酮.DFT计算结果也阐明反应过程中自加速现象的产生源于单位点Co处活性氧物种(O^(*))的生成.该活性氧物种在乙苯、苯甲醛和1-苯乙醇的氧化途径中均能自发生成,并且该物种类似“引发剂”促使后续更多链式反应的发生,在乙苯氧化反应过程中具有非常重要的作用.综上所述,本文为理解芳香族化合物碳-氢键选择氧化实验现象与催化作用机制提供了有益见解,可为理性设计开发更高效的催化剂提供新思路.

Density Functional Studies of the Reaction of Ytterbium Monocation with Fluoromethane:C-F Bond Activation and Electron-Transfer Reactivity

The potential energy surface and reaction mechanism corresponding to the reaction of ytterbium monocation with fluoromethane, which represents a prototype of the activation of C-F bond in fluorohydrocarbons by bare lanthanide cations, have been investigated for the first time by using density functional theory. A direct fluorine abstraction mechanism was revealed, and the related thermochemistry data were determined. The electron-transfer reactivity of the reaction was analyzed using the two-state model, and a strongly avoided crossing behavior on the transition state region was shown. The present results support the reaction mechanism inferred from early experimental data and the related thermochemistry data can provide a guide for further experimental researches.

An Extended Cu(Ⅱ) Complex Structure Sustained by Hydrogen Bonding and C-H…π Interactions

The title complex [Cu（L1）（L2）（H2O）]·H2O（1,HL1 = N-（imino（pyridin-2-yl）me-thyl）picolinamidine）,HL2 = salicylic acid） has been obtained by volatilization method with L1 prepared from 2,4,6-tripyridyl-1,3,5-triazine in situ.1 was fully characterized by single-crystal X-ray diffraction,elemental analysis and FT-IR.This complex exhibits a three-dimensional frame-work constructed through hydrogen bonding and C-H···π stacking interactions.The cyclic voltametric behavior of complex 1 was also investigated.1 belongs to the monoclinic system,space group P21/c with a = 15.112（5）,b = 7.115（2）,c = 19.899（6） ,β = 112.32°,V = 1979.4（11） 3,Mr = 460.94,Dc = 1.540 g/cm3,F（000） = 948,μ = 1.146 mm-1,Z = 4,the final R = 0.0612 and wR = 0.1813 for 2510 observed reflections with I 2σ（I）.

The Effect of Elevated Temperature on Bond Performance of Alkali-activated GGBFS Paste

The main reaction products were investigated by analysis of microstructure of alkali-activated ground granulated blast furnace slag （GGBFS） paste. An experimental research was performed on bond performance of alkali-activated GGBFS paste as a construction adhesive after exposure to 20-500℃. Through XRD analysis, a few calcium silicate hydrate, hydrotalcite and tetracalcium aluminate hydrate were determined as end products, and they were filled and packed each other at room temperature. In addition, akermanite dramatically increased at 800 ~C and above. The two key parameters, the ultimate load Pu.T and effective bond length Le, were determined using test data of carbon fiber-reinforced polymer （CFRP）-to-concrete bonded joints at elevated temperature. The experimental results indicate that the ultimate load Pu.T remains relatively stable initially and then decreases with increasing temperature. The effective bond length Le increases with increasing temperature except at 300℃. The proposed temperature-dependent effective bond length formula is shown to closely represent the test data.

Biphasical Force-Dependent CD40 L Ligation-Induced Activation of Integrin α5β1 under Flows

As a key regulator of immune response,CD40 L is usually associated with chronic disease-related inflammation,autoimmune diseases and malignant diseases.Receptor recognition of platelet CD40 L is the initial event that mediates platelet aggregation and leukocyte immune response.Unlike soluble CD40 L,the interaction between transmembrane platelet CD40 L and its receptors occurs within the cell junction surface,usually,in a physiological and pathological high blood flow shear stress environment.This two-dimensional reaction kinetics should be a mechano-chemical coupling process.In addition to its classical receptor CD40,CD40 L also binds to receptorα5β1,CD40 L can bind to the resting state of integrinα5β1,but the mechanical regulation mechanism of integrinα5β1 activation under fluid shear stress remains unclear.We assume that the force can promote CD40 L-inducedα5β1 activation.To check this hypothesis,we performed flow chamber experiment to investigate interaction of CD40 L andα5β1.In experiments,the bottom of the flow chamber is functionalized by a suitable concentration of CD40 L,and the fiber spheres of 6μm diameter was coated withα5β1.The selection of CD40 L concentration was based on the observation that as many tether events ofα5β1-coated spheres as possible were observed rather than stable adhesion events of these spheres.Theα5β1-coated sphere suspension was poured over the CD40 L-coated substrates in the flow chamber under different shear rates.A high-speed camera was used to observe and record tether events of fiber spheres at a rate of 100 frames per second.According to our affinity state transition model for integrin,the data were analyzed to obtain the rate of integrin activation and its mechanical regulation characteristics.Our results demonstrated that the interaction betweenα5β1 and CD40 L is biphasic force-dependent,showing mechano-chemical regulation mechanism of'Catch-slip bond'transition.The affinity jumping model was well fitted with the data obtained from flow chamber experiment at various wall shear stresses.We found that,CD40 L ligation-induced jumping ofα5β1 affinity state from low to medium(or high)one will occur within 0.5-1.0 second,resulting in prolonging of bond lifetimes.And,frequency distribution of the tether events number with tether lifetime under each force,exhibits obvious doublet peaks,one within 0.5-1 s and second within 1.5-2.5 s,indicating theα5β1 affinity state transform from low to high one.The probability distribution of the tether lifetime under different shear forces are not linear,and exists a turning point,which shows that the rate ofα5β1 dissociation from CD40 L is fast first,and then become slow,showing a force-induced conformation transformation of the integrinα5β1 from low affinity state to high affinity one.Our findings suggest that,the continuous force stimulation will quickly cause the affinity state change of integrinα5β1. The dissociation rate of theα5β1/CD40 L complex decreases first and then increases with wall shear stress,exhibiting a'Catch-slip bond'transformation of interaction betweenα5β1-CD40 L.This mechanical regulation mechanism exists in interaction of CD40 L not only toα5β1 at low affinity state but also to one at high affinity state.Our results should be useful in understanding the mechanical regulation mechanism of a5β1-CD40 L interaction-mediated cellular immune response and inflammatory processes.

High Activated Mineral Admixture Slurry Made by Wet-discharged Fly-ash Promoted by Matrix Bonding Component

The mineral admixture slurry was made by wet-discharged fly-ash （WDFA） promoted by matrix bonding component （MBC）, and the strengths, hydration products change （XRD, SEM） of cement paste made by the slurry were studied. The results indicate that in the process of wet-milling preparation, there is a prime proportion （70︰30） between wet-discharged fly-ash and matrix bonding component in the slurry. The physical activation of wet-milling and chemical activation of modified agents accelerate the hydration of cement including the cement and mineral which has not hydrated completely in the matrix bonding component. And the hydrated part of matrix bonding component can play the function of inducing crystallization, which can accelerate secondary hydration reaction of fly-ash.

STUDIES OF QUANTUM CHEMISTRY CALCULATION ON VALENCE-BOND STRUCTURE AND HYDRATION ACTIVTY OF C_(12)A_7

The structure, chemical bonds and hydra-tion activity of C12A were studied by SCC-DV-Xa method of computational quantum chemistry. The calculated results show that Ca-O bond will be first broken off when C12A hydrates, the reactivity of Al(2)O4 tetrahedron is superior to that of Al(1)O4 tet, thedron and the rupture of the Al-O-Al chain composed of two types of AlO4 tetrahedra under the action of water lies in the very weak Al(2)-O(2) bonds. the Al-O bond strength of C12A7 is between C3A and C11A7·CaF2.

Study on Synthesis and Herbicidal Activity of Heterocyclic Compounds Containing P-P Bond

N,N′-diphenylurea reacted with phosphorus trichloride and phenyl dichlorophosphane giving the heterocyclic compounds 1 and 2 with a direct phosphorus-phosphorus bond (P-P bond), respectively. The new compounds were characterized by elementary analysis, NMR and IR spectra. The results of preliminary bioassay showed that these heterocycles possess selective herbicidal activity at 1.5 kg/hm2.

单原子合金对烷基C-H键活化调控的理论研究

单原子合金是指活性金属原子分散在Cu、Ag或Au载体上所构成的催化剂,近年来已成为单原子催化研究中的一颗“新星”.单原子合金上孤立活性位点与载体金属的电子结构不同,具有奇异的电子结构,故通常表现出独特的催化行为。目前尚缺乏一种可靠的单原子合金催化特性描述符.本文系统地考察了甲烷、丙烷和乙苯在15种Rh、Ir、Ni、Pd和Pt掺杂Cu(111)、Ag(111)和Au(111)单原子合金上初始C-H键活化.密度泛函计算表明,烷基C-H键的活化能垒与d带中心和H原子吸附相关较差,而与反应能之间相关性较好.理论分析表明,C原子在顶位的吸附与C-H活化过渡态之间存在着轨道相互作用的相似性,不仅涉及到对d,2轨道给予,也涉及day/dy≥轨道的元反馈.据此,C原子吸附能与甲烷、丙烷和乙苯C-H键活化能也具有很强的相关性(R2>0.9).

Theoretical verification of intermolecular hydrogen bond induced thermally activated delayed fluorescence in SOBF-OMe

Thermally activated delayed fluorescence(TADF)molecules have attracted great attention as high efficient luminescent materials.Most of TADF molecules possess small energy gap between the first singlet excited state(S_(1))and the first triplet excited state(T_(1))to favor the up-conversion from T_(1)to S_(1).In this paper,a new TADF generation mechanism is revealed based on theoretical simulation.By systematic study of the light-emitting properties of SOBF-OMe in both toluene and in aggregation state,we find that the single SOBF-OMe could not realize TADF emission due to large energy gap as well as small up-conversion rates between S_(1)and T_(1).Through analysis of dimers,we find that dimers with intermolecular hydrogen bond(H-bond)are responsible for the generation of TADF,since smaller energy gap between S_(1)and T_(1)is found and the emission wavelength is in good agreement with experimental counterpart.The emission properties of SOBF-H are also studied for comparison,which reflect the important role of H-bond.Our theoretical results agree ith experimental results well and confirm the mechanism of H-bond induced TADF.

Investigation of Intermolecular C-H···Halogen Hydrogen Bonded Supramolecular Assemblies in Three Copper(Ⅰ) Complexes Formed by 3,3'-Dimethoxy-6,6'-dimethyl-2,2'-bipyridine Ligand

Three new crystalline compounds 1-3 were successfully obtained by the reactions of 3,3＇-dimethoxy-6,6＇-dimethyl-2,2＇-bipyridine ligand（dmbp） with the corresponding Cu（Ⅰ） salts.Crystal data for 1：orthorhombic Pbca,a = 18.5858（12）,b = 8.1821（5）,c = 20.6066（13） ,V = 3133.7（3） 3,Z = 8,Dc = 1.843 g/cm3,F（000） = 1696,μ = 3.366 mm-1,the final R = 0.0223 and wR = 0.0542.Crystal data for 2：Orthorhombic Pbca,a = 18.7883（16）,b = 8.3249（7）,c = 19.0294（17） ,V = 2976.4（4） 3,Z = 8,Dc = 1.731 g/cm3,F（000） = 1552,μ = 4.154 mm-1,the final R = 0.0279 and wR = 0.0680.Crystal data for 3：monoclinic P21/c,a = 13.812（10）,b = 9.910（7）,c = 23.444（17） ,β = 104.3350（10）°,V = 3090（4） 3,Z = 4,Dc = 1.476 g/cm3,F（000） = 1408,μ = 1.588 mm-1,the final R = 0.0479 and wR = 0.1081.The results of X-ray crystallographic analysis revealed that C14H16ICuN2O2（1） and C14H16BrCuN2O2（2） are isostructural compounds with the dimers connected by C-H···halogen hydrogen bonds to generate a three-dimensional（3D） supramolecular network in 1 and a two-dimensional（2D） sheet structure in 2,respectively,while the mononuclear complex C28H32Cl2Cu2N4O4（3） is ionic.In 3,the [Cu（dmbp）2]＋ cations and [ClCuCl]-anions are connected by C-H···Cl hydrogen bonds to form a one-dimensional（1D） chain along the a axis.Therefore,in the three complexes,the C-H···halogen hydrogen bonds dominate their crystal structures.Additionally,The UV luminescent properties of complexes 1-3 were investigated.

A FACILE SYNTHESIS OF 2-TRIFLUOROMETHYLPYRROLE VIA 1,3-DIPOLAR CYCLOADDITION REACTION OF 2-TRIFLUOROMETHYLOXAZOLONE AND THE ACTIVATED CARBON-CARBON MULTIPLE BOND

The 1.3-dipolar cycloaddition reaction of 2-trifluoromethyl- oxazolone and the activated carbon-carbon multiple bond was studied and gave a convenient way to synthesize 2-trifluoromethylpyrrole derivatives.