C-H bond activation of propane on Ga_(2)O_(2)^(2+) in Ga/H-ZSM-5 and its mechanistic implications

Propane dehydrogenation(PDH)on Ga/H-ZSM-5 catalysts is a promising reaction for propylene production,while the detail mechanism remains debatable.Ga_(2)O_(2)^(2+) stabilized by framework Al pairs have been identified as the most active species in Ga/H-ZSM-5 for PDH in our recent work.Here we demonstrate a strong correlation between the PDH activity and a fraction of Ga_(2)O_(2)^(2+) species corresponding to the infrared GaH band of higher wavenumber(GaHHW)in reduced Ga/H-ZSM-5,instead of the overall Ga_(2)O_(2)^(2+) species,by employing five H-ZSM-5 supports sourced differently with comparable Si/Al ratio.This disparity in Ga_(2)O_(2)^(2+) species stems from their differing capacity in completing the catalytic cycle.Spectroscopic results suggest that PDH proceeds via a two-step mechanism:(1)C-H bond activation of propane on H-Ga_(2)O_(2)^(2+) species(rate determining step);(2)β-hydride elimination of adsorbed propyl group,which only occurs on active Ga_(2)O_(2)^(2+) species corresponding to GaHHW.

Oxidative co-dehydrogenation of ethane and propane over h-BN as an effective means for C-H bond activation and mechanistic investigations

Hexagonal boron nitride(h-BN)is a highly selective catalyst for oxidative dehydrogenation of light alkanes to produce the corresponding alkenes.Despite intense recent research effort,many aspects of the reaction mechanism,such as the observed supra-linear reaction order of alkanes,remain unresolved.In this work,we show that the introduction of a low concentration of propane in the feed of ethane oxidative dehydrogenation is able to enhance the C_(2)H_(6) conversion by 47%,indicating a shared reaction intermediate in the activation of ethane and propane.The higher activity of propane makes it the dominant radical generator in the oxidative co-dehydrogenation of ethane and propane(ODEP).This unique feature of the ODEP renders propane an effective probe molecule to deconvolute the two roles of alkanes in the dehydrogenation chemistry,i.e.,radical generator and substrate.Kinetic studies indicate that both the radical generation and the dehydrogenation pathways exhibit a first order kinetics toward the alkane partial pressure,leading to the observed second order kinetics of the overall oxidative dehydrogenation rate.With the steady-state approximation,a radical chain reaction mechanism capable of rationalizing observed reaction behaviors is proposed based on these insights.This work demonstrates the potential of ODEP as a strategy of both activating light alkanes in oxidative dehydrogenation on BN and mechanistic investigations.

Site-specific deposition creates electron-rich Pd atoms for unprecedented C-H activation in aerobic alcohol oxidation

Here,we demonstrate a photochemical strategy to site-specifically deposit Pd atoms on Au nanoparticles.The high-sensitivity low-energy ion scattering spectra combined with the X-ray photoelectron spectra reveal that the surface electronic structure of Pd can be continuously regulated by tailoring the Pd-to-Au molar ratio and the location of Pd atoms in Au Pd nanoparticles.It is revealed that electron-rich Pd atoms are considerably more active than the net Pd atoms in aerobic alcohol oxidation.Remarkably,the catalyst with the most electron-rich Pd sites(binding energy downshift:1.0 e V)exhibits an extremely high turnover frequency(~500000 h-1 vs 12000 h-1 for that with net Pd atoms)for solvent-free selective oxidation of benzyl alcohol,which is,to the best of our knowledge,the highest value ever reported.Kinetic studies reveal that electron-rich Pd atoms can accelerate the oxidation of benzyl alcohol by facilitating C-H cleavage,as indicated by the significant reduction in the activation energy as compared to net Pd atoms.

A Mechanistic Switch in C-H Bond Activation by Elusive Fe^(V)(O)(TAML)Reaction Intermediate:A Theoretical Study

The divergent behavior of C-H bond oxidations of aliphatic substrates compared to those of aromatic substrates shown in Gupta’s experiment was mechanistically studied herein by means of density functional theory calculations.Our calculations reveal that such difference is caused by different reaction mechanisms between two kinds of substrates(the aliphatic cyclohexane,2,3-dimethylbutane and the aromatic toluene,ethylbenzene and cumene).For the aliphatic substrates,C-H oxidation by the oxidant Fe^(V)(O)(TAML)is a hydrogen atom transfer process;whereas for the aromatic substrates,C-H oxidation is a proton-coupled electron transfer(PCET)process with a proton transfer character on the transition state,that is,a proton-coupled electron transfer process holding a proton transfer-like transition state(PCET(PT)).This difference is caused by the strongπ-πinteractions between the tetra-anionic TAML ring and the phenyl ring of the aromatic substrates,which has a“pull”effect to make the electron transfer from substrates to the Fe=O moiety inefficient.

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.

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.

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）.

Catalytic C-H activation-initiated transdiannulation:An oxygen transfer route to ring-fluorinated tricyclic γ-lactones

Catalytic C–H activation-initiated annulation reactions have emerged as a versatile strategy for the efficient construction of diverse ring structural units and complex cyclic molecules in synthetic chemistry.Herein,we describe a new Rh(Ⅲ)-catalyzed C–H activation-initiated transdiannulation reaction of N,Ndimethyl enaminones with gem-difluorocyclopropenes in the presence of H_(2)O,enabling a facile and oxygen transfer access to ring-fluorinated tricyclicγ-lactones with a 6-5 ring-junction tetrasubstituted stereocenter.This approach features bond-forming/annulation efficiency,good functional group tolerance and complete regioselectivity,which may include a complex process consisting of Rh(Ⅲ)-catalyzed C(sp2)–H activation,cyclic alkene insertion,defluorinated ring-opening of gem-difluorocyclopropane,intramolecular oxygen transfer,intramolecular cyclization and oxidative hydration.

基于过硫酸钠氧化的烯丙位C-H键官能团化的研究

设计一种Na_(2)S_(2)O_(8)与金属Cu^(2+)和Co^(2+)催化氧化的交叉脱氢偶联反应,从而实现烯丙位C-H键官能团化的新方法。研究发现,以0.2当量CuSO 4和0.1当量CoCl 2为催化剂,2.0当量Na_(2)S_(2)O_(8)为氧化剂,乙腈为溶剂,80℃下进行环己烯与乙酰丙酮的交叉脱氢偶联反应,可以实现环己烯烯丙位C-H键的直接官能团化,此方法也适用于与环己烯和乙酰丙酮相似结构的化合物,产率41%~56%。该方法成本低、毒性小、操作简单且易于实现烯丙位C-H键的直接官能团化,具有底物及亲核试剂应用的广泛性。

Ru(II)-Catalyzed ortho C-H Allylation of N-Aryl-7-azaindoles with 2-Methylidene Cyclic Carbonate

A Ru(II)-catalyzed ortho allylation reaction of N-aryl-7-azaindole with readily available 2-methylidene cyclic carbonate has been developed.This reaction is an effective pathway for synthesizing 7-azaindole derivatives with a wide scope of substrates and high yields.In addition,the method can be extended to the allylation of other heterocyclic compounds and several cyclic carbonates,highlighting the practicality of this strategy for synthesis.

韭花精油主成分对单增李斯特氏菌的抑菌活性和抑菌机理

以韭花精油两种主成分(烯丙基甲基二硫醚和二甲基三硫醚)为研究对象,通过最小抑菌质量浓度(MIC)、最小杀菌质量浓度(MBC)、细菌细胞形态等研究其对单增李斯特氏菌的抑菌活性和抑菌机理。结果表明:两种主成分的MIC均为1.0 mg/mL,MBC均为2.0 mg/mL,且当其质量浓度为2.0 mg/mL时均会严重损坏单增李斯特氏菌的细胞形态和细胞膜结构;用质量浓度为4.0 mg/mL的烯丙基甲基二硫醚和二甲基三硫醚分别处理单增李斯特氏菌细胞,其β-半乳糖苷酶和蛋白质泄露量均显著上升,ATP酶活性(0.52 U/mg prot和0.55 U/mg prot)均明显低于对照组(3.05 U/mg prot,P<0.05);经两种主成分处理后,单增李斯特氏菌的DNA质量浓度均明显下降。由此可知,两种主成分主要通过破坏细胞膜结构、抑制ATP酶活性、降低DNA质量浓度等实现对单增李斯特氏菌活性的抑制。

烯丙基醚化酚醛亚胺树脂的固化动力学研究

采用差示扫描量热仪测定了不同升温速率下烯丙基醚化酚醛亚胺树脂(APMI-F树脂)的DSC曲线,用非等温热力学的研究方法研究了APMI-F树脂的固化反应动力学。用T-β外推法确定了APMI-F树脂的固化反应的起始温度Ti、峰值温度Tp和终止温度Tf,并将其作为探究APMI-F树脂固化工艺的依据。通过Kissinger法和Starink法求得APMI-F树脂的表观活化能,由Starink法得到不同固化度下的表观活化能,并将其与试验数据对比,以验证固化动力学模型的准确性。研究结果表明:(1)利用外推法确定了APMI-F树脂固化反应的Ti、Tp和Tf分别为161.09、226.81、263.42℃;(2)Starink法求得的平均活化能要高于Kissinger法所得数据;(3)在固化反应过程中,随着固化程度的升高,APMI-F树脂的表观活化能呈现先降低后升高的趋势,固化初期活化能因黏度的降低而降低,随着交联度的提高,链段运动受到限制导致活化能渐渐升高;(4)采用Málek法成功地建立了APMI-F树脂的固化动力学模型,通过与试验数据对比,发现该模型能够很好地描述APMI-F树脂的固化过程。

Derivation of Benzothiadiazine-1,1-dioxide Scaffolds via Transition Metal-Catalyzed C-H Activation/Annulation

Comprehensive Summary Benzothiadiazine-1,1-dioxide scaffold is bioactive framework with wild utility and applications.Synthesis of benzothiadiazine-fused isoquinoline derivatives and spiro benzothiadiazine derivatives through transition metal-catalyzed C—H activation/annulation was reported.3-Phenyl-2H-benzothiadiazine-1,1-dioxide was used as the reaction substrate,and vinylene carbonate and 4-diazopyrazolone were used as the coupling reagents,respectively.This strategy provides straightforward access to complex N-heterocycles in a highly efficient and simple manner.

The marriage of dual-acceptor strategy and C-H activation polymerization:naphthalene diimide-based n-type polymers with adjustable molar mass and decent performance

The development of readily accessible high-mobility n-type semiconducting polymers is in great demand for realizing highperformance p-n junction-based organic electronics.In this study,we demonstrate that with the combination of dual-acceptor strategy and C-H direct arylation polymerization(DAr P),unipolar n-type semiconducting polymers can be conveniently synthesized.By tuning the monomer concentration,three dual-acceptor polymers,namely,poly(naphthalene diimide-alt-dithiophenyl pyrrolopyrrole-dione)(PNDI-DPP),poly(naphthalene diimide-alt-dithiophenyl isoindigo)(PNDI-IID),and poly(naphthalene diimide-alt-dithiophenyl bezothiadiazole)(PNDI-BT)can be obtained via C-H activation with decent number average molecular weight of~10 to 30 kg mol^(-1)and relatively narrow polydispersity index of~2.In addition,these polymers are defect-free in nature as evidenced by the nuclear magnetic resonance.Moreover,we attribute the different molar masses of the three copolymers under the same DAr P condition to the differentα-C-H acidity,which may stem from different electronwithdrawing capability of the hydrogenated acceptor units.Furthermore,the influence of the hydrogenated acceptor monomers on the optical,electrochemical and charge transporting properties is comprehensively studied.Among the three dual-acceptor polymers,PNDI-BT demonstrates the highest electron mobilities of up to 0.6 cm^(2)V^(-1)s^(-1)in unipolar n-type organic transistors because of its relatively planar backbone,larger overlaps of the lowest unoccupied molecular orbital and strong H-aggregation.Note that the transistor performance of PNDI-BT synthesized via C-H activation in this study is at least comparable to the one made by conventional C(sp^(2))-C(sp^(2))Stille or Suzuki cross-coupling polymerization.This study demonstrates the presented protocol can be a useful platform for sustainable and convenient synthesis of high-performance n-type semiconducting polymers.

Mechanistic Study of Palladium-Catalyzed Oxidative C-H/C-H Coupling of Polyfluoroarenes with Simple Arenes

Pd-catalyzed oxidative C-H/C-H coupling reaction is an emerging type of C-H acti- vation reaction, which attracts great interests because both reaction partners do not re- quire pre-functionalization. In the present study, we employed DFT methods to investigate the mechanism of Pd（OAc）2-catalyzed oxidative C-H/C-H coupling of pentafluoroben-zene with benzene. Four possible pathways were examined in the C-H activation part： path A benzene-pentafluorobenzene mechanism （C-H activation of benzene occurs before the C-H activation of pentafluorobenzene）, path B pentafluorobenzene-benzene mechanism （C-H activation of benzene occurs after the C-H activation of pentafluorobenzene）, path C benzene-pentafluorophenylsilver mechanism （C-H activation of benzene and subsequent transmetalation with pentafiuorophenyl silver complex）, path D pentafiuorophenylsilver- benzene mechanism （transmetalation with pentafluorophenyl silver complex and subsequent C-H activation of benzene）. Based on the calculations, the sequences of two C-H activation steps are found to be different in the oxidative couplings of same substrates （i. e. pentafiu- orobenzene and benzene） in different catalytic systems, where the additive Ag salts played a determinant role. In the absence of Ag salts, the energetically favored pathway is path B （i.e. the C-H activation of pentafluorobenzene takes place before the C-H cleavage of benzene）. In contrast, with the aid of Ag salts, the coordination of pentafluorophenylsilver to Pd center could occur easily with a subsequent C-H activation of benzene in the second step, and the second step significantly raises the whole reaction barrier. Alternatively, in the presence of Ag salts, the kinetically preferred mechanism is path C （i. e. the C-H activation of benzene takes place in the first step followed by transmetalation with pentafluorophenyl- silver complex）, which is similar to path A. The calculations are consistent with the H/D exchange experiment and kinetic isotope effects. Thus the present study not only offers a deeper understanding of oxidative C-H/C-H coupling reaction, but also provides helpful insights to further development of more efficient and selective oxidative C-H/C-H coupling reactions.

TBHP氧化烯丙位sp^(3) C-H键制备其官能团化衍生物

目的本文研究以TBHP(70%水溶液)氧化烯丙位sp^(3) C-H键,过渡金属催化实现其C-C官能团化,并成功合成一系列衍生物。方法以0.25倍当量的CuCl、0.1倍当量的CoCl2为催化剂,乙腈为溶剂,2倍当量TBHP为氧化剂,1.5倍当量分子筛为添加剂,在80℃反应条件下,可以有效地促进环己烯烯丙位C—H键的活化进而完成与乙酰丙酮的交叉脱氢偶联(CDC)反应。结果该体系也适用于其他与环己烯结构相似的环状烯烃烯丙位C-H键的官能团化反应,产率在60%~88%。结论该反应具有经济、条件温和等优点。

Proposal of an Amide-Directed Carbocupration Mechanism for Copper-Catalyzed meta-Selective C-H Arylation of Acetanilides by Diaryliodonium Salts

We examined the puzzling mechanism for Cu-catalyzed meta-C-H arylation reaction of anilides by diaryliodonium salts through systematic theoretical analysis. The previously proposed anti-oxy-cupration mechanism featuring anti-1,2- or anti-1,4-addition of cuprate and oxygen to the phenyl ring generating a meta-cuprated intermediate was excluded due to the large activation barriers. Alternatively, a new amide-directed carbocupration mechanism was proposed which involves a critical rate- and regio-determining step of amide-directed addition of the Cu（III）-aryl bond across the phenyl C2=C3 double bond to form an orthocuprated, meta-arylated intermediate. This mechanism is kinetically the most favored among several possible mechanisms such as ortho-or para-cupration/migration mechanism, direct meta C-H bond cleavage mediated by Cu（III） or Cu（I）, and Cu（III）-catalyzed ortho-directed C-H bond activation mechanism this mechanism has been shown to Furthermore, the predicted regioselectivity based on favor the meta-arylation that is consistent with the experimental observations.

Photocatalytic Methane Conversion:Insight into the Mechanism of C(sp^(3))-H Bond Activation

Mild and direct conversion of methane into high value-added products is a desired goal for chemistry,energy,and environment.The active species generated in the photocatalytic reaction system under mild conditions activate the inert C-H bond in methane and promote methane conversion.This review focuses on the developed mechanisms for C(sp^(3))-H bond activation in photocatalytic methane conversion,including radical and active site mechanisms.Particular emphasis is placed on the detailed summary of mechanism,characterization method,and corresponding application in photocatalytic methane conversion.We also discuss the challenges and prospects for future direction on C(sp^(3))-H bond activation mechanism in photocatalytic methane conversion.This review aims to promote the development of photocatalytic methane conversion and provides guidance for the design of high-efficiency photocatalysts.

Theoretical studies and industrial applications of oxidative activation of inert C-H bond by metalloporphyrin-based biomimetic catalysis

High costs and low catalytic efficiency of metalloporphyrins, which are an analogue of cytochrome P450 enzyme, are the bot-tlenecks in the industrialization of biomimetic hydrocarbon oxidation reactions. The basic principle and research technique of physical organic chemistry were applied to the process of biomimetic oxidation of hydrocarbon catalyzed by metalloporphyrins. This biomimetic technology could be adapted to bulk chemicals production by developing the new methods for efficient scale-up synthesis of metalloporphyrins, new pathways for molecular oxygen activation on an industrial scale and new approaches to elevate the catalytic efficiency of metalloporphyrins. This review mainly focuses on research carried out in our group.

π-Extension of Isoindigos(IIDs)through C—H/N—H Activation and Alkyne Annulation

Isoindigo(IID)is widely used as organic dye and conjugated unit in opto-electronic materials.Functionalization of IID to increase its structural complexity is demanding for obtaining diversity properties.Herein,we developed a direct C-H/N-H activation method of IIDs via double alkyne annulations and synthesizedπ-extended IIDs with two pairs of 5/7 membered rings.The structure of theπ-extended IIDs was characterized and confirmed by^(1)H NMR,^(13)C NMR,HRMS and X ray crystal analysis.Their physical properties were characterized by UV-vis absorption,cyclic voltammetry and thermogravimetric analysis.The absorption coefficient of the annulated products enhanced significantly compared with the non-annulated analogue.