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.

Insight into the photoexcitation effect on the catalytic activation of H_(2) and C-H bonds on TiO_(2)(110)surface

Semiconductor photocatalysis holds great promise for breaking the inert chemical bonds under mild condition;however,the photoexcitation-induced modulation mechanism has not been well understood at the atomic level.Herein,by performing the DFT+U calculations,we quantitatively compare H_(2) activation on rutile TiO_(2)(110)under thermo-versus photo-catalytic condition.It is found that H2 dissociation prefers to occur via the heterolytic cleavage mode in thermocatalysis,but changes to the homolytic cleavage mode and gets evidently promoted in the presence of photoexcited hole(h^(+)).The origin can be ascribed to the generation of highly oxidative lattice O-radical(O_(br)^(·−))with a localized unoccupied O-2p state.More importantly,we identify that this photo-induced promotion effect can be practicable to another kind of important chemical bond,i.e.,C-H bond in light hydrocarbons including alkane,alkene and aromatics;an exception is the C(sp^(1))-H in alkyne(HC≡CH),which encounters inhibition effect from photoexcitation.By quantitative analysis,the origins behind these results are attributed to the interplay between two factors:C-H bond energy(E_(bond))and the acidity.Owing to the relatively high E_(bond) and acidity,it favors the C(sp^(1))-H bond to proceed with the heterolytic cleavage mode in both thermo-and photo-catalysis,and the photoexcited O_(br)^(·−)is adverse to receiving the transferred proton.By contrast,for the other hydrocarbons with moderate/low E_(bond),the O_(br)^(·−)would enable to change their activation mode to a more favored homolytic one and evidently decrease the C-H activation barrier.This work may provide a general picture for understanding the photocatalytic R-H(R=H,C)bond activation over the semiconductor catalyst.

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.

ATR-FTIR Analysis on Aliphatic Hydrocarbon Bond(C-H)For­mation and Carboxyl Content during the Ageing of DC Air Plasma Treated Cotton Cellulose and Its Impact on Hydrophilicity

The surface of the cotton fabric was modified using a direct current(DC)air plasma treatment and hence enhances its hydrophilicity.The Box-Behnken approach(design expert software)was used to optimise the input process parameters.The sample prepared under optimized condition is subjected to ATR-FTIR and Field Emission Scanning Electron Microscopy(FESEM)studies in order to determine the changes in hydrogen bond energies(EH),Total Crystallinity Index(TCI),Hydrogen Bond Intensity(HBI),Lateral Order Index(LOI),functionalization,lattice parameters(a,b,c&β),degree of crystallinity(in%)and surface etching.The ageing of this sample has been studied by comparing the values of carboxyl content and AC-C/AC-O-C ratio calculated using data extracted from ATR-FTIR spectra of the sample recorded periodically for one month.

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.

C-H…X-C bonds in alkyl halides drive reverse selectivities in confined spaces

Binding of non-activated alkyl halides(2-20)in water-soluble cavitand(1)through supramolecular forces is here reported,with emphasis on the role of size and polarizability of the halogen atom in the formation of intramolecular C-H hydrogen bonds in confined spaces.Rare reverse affinity in water(RI<RBr<RCl)is surprisingly observed for the more water-soluble short alkyl halides in dynamic open-ended containers.Competitive bindings and theoretical calculations confirm the unusual selectivity and the presence of C-H hydrogen bonds in non-activated systems for the first time,pointing out the importance and effect of subtle forces on molecular recognition in confined spaces.

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）.

Light-induced phosphine-catalyzed asymmetric functionalization of benzylic C–H bonds

Despite rapid development in the past two decades,there are still some unsolved synthetic challenges in the field of phosphine catalysis.In this report,through photo-induced activation of ortho-alkyl aromatic ketones,we achieved highly enantioselective functionalization of substrates bearing a benzylic C–H bond.In the presence of amino acid-derived bifunctional phosphine catalysts,a range of benzylic allylation products were obtained in good yields and with excellent enantioselectivities.The strategy disclosed herein offers new insight into the activation and functionalization of pronucleophiles containing less acidic C–H bonds in the domain of phosphine catalysis and beyond.

Polyoxometalate-encapsulated metal-organic frameworks with diverse cages for the C-H bond oxidation of alkylbenzenes

Exploring new heterogeneous catalysts to achieve efficient C-H bond oxidation is momentous in industrial chemical production.Herein,three Fe-incorporated polyoxometalate-encapsulated metal-organic frameworks(POM@MOFs),[Fe(H_(2)O)_(3)(dtb)][Fe(dtb)_(2)][HBW_(12)O_(40)]-12H_(2)O(1),[Fe(H_(2)O)2(dtb)]_(2)[Fe(dtb)_(2)(Hdtb)][SiW^(Ⅵ)_(9)W^(Ⅴ)_(3)O_(40)]·16H_(2)O(2),[Fe(H_(2)O)_(2)]_(4)(dtb)_(5)[PMo^(Ⅵ)_(11)Mo^(Ⅴ)O_(40)]_(2)·18H_(2)O(3),(dtb=1,4-di[4H-1,2,4-triazol-4-yl]-benzene),were hydrothermally synthesized for catalytic C-H bond oxidation.They exhibited three-dimensional(3-D)POM-based metal-organic host-guest frameworks with diverse cages.In compound 1,cationic metal-organic frameworks constructed by binuclear[Fe_(2)(dtb)_(6)(H_(2)O)_(2)]^(4+)clusters and dtb ligands present a pcu alpha-Po primitive cubic topological net and abundant twisted quadrangular prism-shaped cages,in which the monoprotonated[HBW_(12)O_(40)]^(4-)polyoxoanions are encapsulated.In compound 2,two-dimensional(2-D)cationic metal-organic layers constructed by trinuclear[Fe_(3)(dtb)_(6)(H_(2)O)_(4)]^(6+)clusters and dtb ligands display a sql/Shubnikov tetragonal plane net topology,in which the rhomboid-shaped metal-organic windows in adjacent parallel-arranged 2-D layers are enclosed to form an open parallelepiped cage.The[SiW^(Ⅵ)_(9)W^(Ⅴ)_(3)O_(40)]^(7-)poly-oxoanions locate in the parallelepiped cages between 2-D bilayers.In compound 3,the 3-D cationic metal-organic frameworks constructed by binuclear[Fe_(2)(dtb)_(3)(H_(2)O)_(4)]^(4+)clusters and dtb ligands possess a bnn hexagonal BN topology,in which the hexagonal prismatic metal-organic cages accommodate four[PMo^(Ⅵ)_(11)Mo^(Ⅴ)O_(40)]^(4-)poly-oxoanions.Employing diphenylmethane(DPM)oxidation as C-H bond oxidation model reaction,compounds 1-3 displayed distinct catalytic activities owing to the synergistic effect of polynuclear Fe nodes and poly-oxoanions.Among them,[PMo^(Ⅵ)_(11)Mo^(Ⅴ)O_(40)]^(4-)-contained compound 3 exhibited higher catalytic activity than polyoxotungstate-based compounds 1-2 with 99%DPM conversion and 99%benzophenone(BP)selectivity within 6 h as well as good recyclability and structural stability.

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.

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.

The mechanism of hydrogen abstraction by high valence transition metal oxo compounds

We present here a systematic theoretical study to explore the underlying mechanisms of the H abstraction reaction from methane. Various abstracting agents have been modeled, using oxygen radicals and a set of high valence metal oxo compounds. Our calculations demonstrate that although H abstraction from CH3-H by metal oxoes can be satisfactorily fitted into the Polanyi correlation on the basis of oxygen radicals, the mechanisms behind are significantly different. The frontier orbital analyses show that there are three electrons and three active orbitals (3e, 3o) involved in H abstraction by oxygen radicals; whereas an additional orbital of pi(M-O)* is involved in H abstraction by M = O, resulting in a (4e, 4o) interaction. In terms of valence bond state correlation diagram, we find that H abstraction by a metal oxo may benefit from the contribution of ionic resonance structures, which could compensate the penalty of opening the M-O pbond. We believe that these findings can help to design more effective catalysts for the activation of light alkanes. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B. V. and Science Press. All rights reserved.

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.

Vicarious Michael Addition

C-H bond can undergo vicarious Michael addition reaction （VMA） with doubleactivated double bond in the absence of strong base and catalyst under mild conditions. Intramolecular H-bonding, electron-withdrawing inductive effect, and steric hindrance at aposition of nucleophile facilitates C-H addition over N-H addition. By using VMA, high branching multiplicity, novel branching pattern, controllable density and distribution of functional groups can be envisioned for novel dendrimer synthesis.

STUDY OF RAY IRRADIATION ON DIAMOND-LIKE CARBON FILMS

Diamond-like carbon (DLC) films have been deposited on glass substrates usingradio-frequency (rf) plasma deposition method. Gamma -ray, ultraviolet (UV) ray were used toirradiate the DLC films. Raman spectroscopy and infrared (IR) spectroscopy were use to characterizethe changing characteristics of SP^3 C-H bond and hydrogen content in the films due to theirradiations. The results show that, the damage degrees induced by the UV ray on the SP^3 C-H bondsare much stronger than that by the gamma -ray. When the irradiation dose of gamma -ray reaches 1 OX10^4 Gy, the SP^3 C-H bond reduces about 50 percent in number. The square electrical resistance ofthe films is reduced due to the irradiation of UV ray and this is caused by severe oxidation of thefilms. By using the results on optical gap of the films and the fully constrained network theory,the hydrogen content in the as-deposited films is estimated to be l0-25at. percent.

Synthesis, Structure and Properties of Benzo[1,2-f:5,4-f＇]- diquinoline Derivatives： A Remarkably Strong Intramolecular C-H...O Hydrogen Bond

A series of benzo[1,2-f：5,4-f＇]diquinoline derivatives were synthesized starting from 2,7-diaminoanthracene, and their structures were determined by NMR, MS spectra and X-ray analysis. They showed a remarkably strong intramolecular C--H...O hydrogen bond, which resulted in an unexpected downfield chemical shift of the aromatic proton in CDCl3. Moreover, a significant fluorescent change of molecule lb in the presence of trifluoroacetic acid （TFA） was also observed.

Syntheses,Characterization and Crystal Structures of Dithiocarbamate-based Mononuclear Palladium(Ⅱ) Complexes

By employing the dithiocarbamate salt （K（PPDC）, where PPDC = 4？-pyridyl-1-pipe-razine-4-dithiocarbamate） as the functional ligand and di-palladium complexes [（N^N）2Pd2（NO3ˉ）2]（NO3ˉ）2 （N^N = 2,2＇-bipyridine, bpy; 4,4＇-dimethylbipyridine, dmbpy） as corner, two novel single metal complexes with Pd（II） centers have been obtained. These organic-metal complexes were characterized by NMR, ESI-MS, elemental analysis, Uv-vis spectra and single-crystal X-ray diffraction analysis. Compound 1？（PF6）2 （[（bpy）Pd（PPDC）]·（PF6）2） crystallizes in triclinic, space group P , a = 8.3968（5）, b = 11.5565（7）, c = 18.2234（11）, α = 97.505（1）, β = 91.424（1）, γ = 106.146（1）o, C22H24N6S2P2F12Pd, Mr = 832.93, V = 1680.58（18） ？3, Z = 2, Dc = 1.646 Mg/m3, μ（MoKα） = 0.863 mm-1, F（000） = 828, the final R = 0.0455 and wR = 0.1390 for 6981 observed reflections with I 〉 2σ（I）. Similarly, compound 2？（PF6）2 （[（dmbpy）Pd（PPDC）]·（PF6）2） also crystallizes in triclinic, space group P , a = 13.9467（3）, b = 14.8390（2）, c = 17.0632（3） ？, α = 81.8680（10）, β = 87.051（2）, γ = 83.4590（10）o, C22H25N5S2P2F12Pd, Mr = 819.93, V = 3470.81（11） ？3, Z = 4, Dc = 1.569 Mg/m3, μ（CuKα） = 7.115 mm-1, F（000） = 1632, the final R = 0.0606 and wR = 0.1637 for 12835 observed reflections with I 〉 2σ（I）. Crystallography reveals that each metal center coordinates with two N atoms from bpy and two S atoms from PPDC in the square coordination mode. In the crystal structure of complex 1, a weak Pd……Pd interaction can be observed. Interestingly, it was also found that the mononuclear moieties of complex 2 could be packed into a 3-D porous framework via multiple intermolecular C–F……H hydrogen-boding interactions which extended in the a, b, and c axes with PF6ˉ anions frozen inside.

New progress in theoretical studies on palladium-catalyzed C-C bond-forming reaction mechanisms

This review reports a series of mechanistic studies on Pd-catalyzed C-C cross-coupling reactions via density functional theory(DFT) calculations.A brief introduction of fundamental steps involved in these reactions is given,including oxidative addition,transmetallation and reductive elimination.We aim to provide an important review of recent progress on theoretical studies of palladium-catalyzed carbon-carbon cross-coupling reactions,including the C-C bond formation via C-H bond activation,decarboxylation,Pd(Ⅱ)/Pd(Ⅳ) catalytic cycle and double palladiums catalysis.

Neutral C–H bond vs. electron pair of N(sp^2): A binding site effect study of macrocycle anion receptor

To evaluate the effect of neutral C–H bond or electron pair of nitrogen atom with sp2hybridization（N（sp2）） involving into the same chemical environment for anion binding, two analogous tetracationic imidazolium macrocycles, namely cyclo[2]（2,6-bis-（1H-imidazol-1-yl）pyridine） [2]（1,3-dimethylenebenzene）（14＋）, and cyclo[2]（2,6-bis-（1H-imidazol-1-yl）pyridine）[2]（2,6-di methylenepyridine）（24＋）were studied in detail as small inorganic anion receptors. The guest anions with different shapes are Cl,N3, NO3, and H2PO4. The host–guest interactions were characterized via1 H NMR spectroscopy,electrospray ionization mass spectrometry（ESI-MS） and single crystal X-ray crystallography. The results implied that macrocyclic hosts with similar backbone but two distinct binding sites（14＋with neutral C–H vs. 24＋with N（sp2）） vary markedly in their response to anions, including the binding modes and association constants. The finding will serve to the construction of new anion receptors, even improve insights into the anion binding process in biology.

A density functional theory study of methane activation on MgO supported Ni_(9)M_(1) cluster:role of M on C-H activation

Methane activation is a pivotal step in the application of natural gas converting into high-value added chemicals via methane steam/dry reforming reactions.Ni element was found to be the most widely used catalyst.In present work,methane activation on MgO supported Ni–M(M=Fe,Co,Cu,Pd,Pt)cluster was explored through detailed density functional theory calculations,compared to pure Ni cluster.CH_(4)adsorption on Cu promoted Ni cluster requires overcoming an energy of 0.07 eV,indicating that it is slightly endothermic and unfavored to occur,while the adsorption energies of other promoters M(M=Fe,Co,Pd and Pt)are all higher than that of pure Ni cluster.The role of M on the first C–H bond cleavage of CH_(4)was investigated.Doping elements of the same period in Ni cluster,such as Fe,Co and Cu,for C–H bond activation follows the trend of the decrease of metal atom radius.As a result,Ni–Fe shows the best ability for C–H bond cleavage.In addition,doping the elements of the same family,like Pd and Pt,for CH_(4)activation is according to the increase of metal atom radius.Consequently,C–H bond activation demands a lower energy barrier on Ni–Pt cluster.To illustrate the adsorptive dissociation behaviors of CH_(4)at different Ni–M clusters,the Mulliken atomic charge was analyzed.In general,the electron gain of CH_(4)binding at different Ni–M clusters follows the sequence of Ni–Cu(–0.02 e)<Ni(–0.04 e)<Ni–Pd(–0.08 e)<Ni–Pt(–0.09 e)<Ni–Co(–0.10 e)<Ni–Fe(–0.12 e),and the binding strength between catalysts and CH_(4)raises with the CH_(4)electron gain increasing.This work provides insights into understanding the role of promoter metal M on thermal-catalytic activation of CH_(4)over Ni/MgO catalysts,and is useful to interpret the reaction at an atomic scale.