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.

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）.

Theoretical Study on the C-H Activation in Decarbonylation of Acetaldehyde by NiL_2(L=SO_3CH_3) Using Density Functional Theory

Density functional theory calculations were carried out to explore the potential energy surface（PES） associated with the gas-phase reaction of Ni L2（L=SO3CH3） with acetone. The geometries and energies of the reactants, intermediates, products and transition states of the triplet ground potential energy surfaces of [Ni, O, C2, H4] were obtained at the B3LYP/6-311＋＋G（d,p） levels in C,H,O atoms and B3LYP/ Lanl2 dz in Ni atom. It was found through our calculations that the decabonylation of acetaldehyde contains four steps including encounter complexation, C-C activation, aldehyde H-shift and nonreactive dissociation. The results revealed that C-C activation induced by Ni L2（L=SO3CH3） led to the decarbonylation of acetaldehyde.

Asymmetric macrocyclization enabled by Rh(Ⅲ)-catalyzed C-H activation:Enantioenriched macrocyclic inhibitor of Zika virus infection

The development of enantioselective C-H macrocyclizations to efficiently access structurally diversified macrocycles is highly desirable,but remain a big challenge.Herein,we reported the first rhodium(Ⅲ)-catalyzed asymmetric intramolecular C-H macrocyclization,enabling the efficient synthesis of structurally diverse enantioenriched macrocycles.This robust enantioselective C-H macrocyclization has a broad functional group tolerance,excellent enantioselectivities(up to 98.5:1.5 e.r.)and a mild reaction condition,releasing CO_(2)as the single by-product.More significantly,the resulting unique enantioenriched19-membered macrocycle 2f was found to demonstrate a potent in vitro anti-Zika virus(ZIKV)activity without obvious cytotoxicity.Further investigation revealed that the anti-ZIKV activity is presumably attributed to an autophagy inhibition in the early stage of viral infection by down-regulating the expression of autophagy related gene Atg12.

Tuning beneficial calcineurin phosphatase activation to counterα-synuclein toxicity in a yeast model of Parkinson’s disease

Calcineurin(CN)is a calcium-and calmodulindependent serine/threonine that has been studied in many model organisms including yeast,filamentous fungi,plants,and mammals.Its biological functions range from ion homeostasis and virulence in lower eukaryotes to T-cell activation in humans by human nuclear factors of activated T-cells.CN is a heterodimeric protein consisting of a catalytic subunit,calcineurin A(Cna1p),which contains an active site with a dinuclear metal center,and a regulatory Ca^(2+) binding subunit called calcineurin B(Cnb1p)required to activate Cna1p.The calcineurin B subunit has been highly conserved through evolution:For example,the mammalian calcineurin B shows 54%identity with calcineurin B from Saccharomyces cerevisiae.

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.

An Efficient Boron Source Activation Strategy for the Low‑Temperature Synthesis of Boron Nitride Nanotubes

Lowering the synthesis temperature of boron nitride nanotubes(BNNTs)is crucial for their development.The primary reason for adopting a high temperature is to enable the effective activation of highmelting-point solid boron.In this study,we developed a novel approach for efficiently activating boron by introducing alkali metal compounds into the conventional MgO–B system.This approach can be adopted to form various low-melting-point AM–Mg–B–O growth systems.These growth systems have improved catalytic capability and reactivity even under low-temperature conditions,facilitating the synthesis of BNNTs at temperatures as low as 850℃.In addition,molecular dynamics simulations based on density functional theory theoretically demonstrate that the systems maintain a liquid state at low temperatures and interact with N atoms to form BN chains.These findings offer novel insights into the design of boron activation and are expected to facilitate research on the low-temperature synthesis of BNNTs.

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.

Effect of external and internal cues on core muscle activation during the Sahrmann five-level core stability test

BACKGROUND Pain in the back or pelvis or fear of back pain may affect the timing or cocontraction of the core muscles.In both static and dynamic movements,the Sahrmann core stability test provides an assessment of core muscle activation and a person's ability to stabilize the lumbopelvic complex.Preparatory cues and images can be used to increase the activation of these muscles.To attain optimal movement patterns,it will be necessary to determine what cueing will give the most effective results for core stability.AIM To investigate the effects of external and internal cues on core muscle activation during the Sahrmann five-level core stability test.METHODS Total 68 participants(21.83±3.47 years)were randomly allocated to an external(n=35)or internal cue group(n=33).Participants performed the Sahrmann fivelevel core stability test without a cue as baseline and the five-level stability exercises with an internal or external cue.External cue group received a pressure biofeedback unit(PBU),and the internal cue group received an audio cue.A Delsys Trigno^(TM)surface electromyography unit was used for muscle activation from the rectus abdominis,external oblique,and transverse abdominis/internal oblique muscles.RESULTS Linear mixed effects model analysis showed that cueing had a significant effect on core muscle activation(P=0.001);however,there was no significant difference between cue types(internal or external)(P=0.130).CONCLUSION Both external and internal cueing have significant effects on core muscle activation during the Sahrmann five-level core stability test and the PBU does not create higher muscle activation than internal cueing.

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.

Mechanistic study of copper-catalyzed intramolecular ortho-C-H activation/carbon-nitrogen and carbon-oxygen cyclizations

Intramolecular ortho-C-H activation and C-N/C-O cyclizations of phenyl amidines and amides have recently been achieved under Cu catalysis. These reactions provide important examples of Cu-catalyzed functionalization of inert C-H bonds, but their mechanisms remain poorly understood. In the present study the several possible mechanisms including electrophilic aro- matic substitution, concerted metalation-deprotonation （CMD）, Friedel-Crafts mechanism, radical mechanism, and proton- coupled electron transfer have been theoretically examined. Cu（II）-assisted CMD mechanism is found to be the most feasible for both C-O and C-N cyclizations. This mechanism includes three steps, i.e. CMD with Cu（II）, oxidation of the Cu（II） inter- mediate, and reductive elimination from Cu（III）. Our calculations show that Cu（II） mediates the C-H activation through an six-membered ring CMD transition state similar to that proposed for many Pd-catalyzed C-H activation reactions. It is also in- teresting to find that the rate-limiting steps are different for C-N and C-O cyclizations： for the former it is concerted metalation-deprotonation with Cu（II）, whereas for the latter it is reductive elimination from Cu（III）. The above conclusions are consistent with the experimental kinetic isotope effects （1.0 and 2.1 for C-O and C-N cyclizations, respectively）, substituent effects, and the reactions under O2-free conditions.

Reductive Coupling of Aryl Halides via C-H Activation of Indene

This paper describes the first case of a reductive coupling reaction with indene,a non-heteroatom olefin used as a reducing agent.The scope of the substrate is wide.The homo-coupling,cross-coupling,and synthesis of 12 and 14-membered rings were realized.The control experiment,indene-product curve and density functional theory calculations showed that the η^(3)-palladium indene intermediate was formed by C-H activation in the presence of cesium carbonate.We speculate that the final product was obtained through a Pd(IV)intermediate or aryl ligand exchange.In addition,we excluded the formation of palladium anion(Pd(0)^(-))intermediates.

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.

Manganese-catalyzed bicyclic annulations of imines and α,β-unsaturated esters via C-H activation

A manganese-catalyzed bicyclic annulation of imines with α,β-unsaturated esters via C–H activation is described, which provides an expedient access to fused β-lactams in one-step operation with high efficiency and good functional group tolerance. Of note, both ketimines and aldimines are amenable to this transformation. Mechanistic studies have identified a five-membered azamanganacycle as the key reaction intermediate.

Direct synthesis of benzoxazinones via Cp*Co(Ⅲ)-catalyzed C-H activation and annulation of sulfoxonium ylides with dioxazolones

A highly novel and direct synthesis of benzoxazinones was developed via Cp*Co(Ⅲ)-catalyzed C-H activation and[3+3]annulation between sulfoxonium ylides and dioxazolones.The reaction is conducted under base-free conditions and tolerates various functional groups.Starting from diverse readily available sulfoxonium ylides and dioxazolones,a variety of benzoxazinones could be synthesized in one step in 32%-75%yields.

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.

Rhodium(Ⅲ)-catalyzed chemodivergent annulations between phenyloxazoles and diazos via C-H activation

Acid-controlled,chemodivergent and redox-neutral annulations for the synthesis of isocoumarins and isoquinolinones have been realized via Rh(Ⅲ)-cataIyzed C—H activation.Diazo compounds act as a carbene precursor,and coupling occurs in one-pot process,where adipic acid and trimethylacetic acid promote chemodivergent cyclizations.

Strategies to achieve effective nitrogen activation

Ammonia serves as a crucial chemical raw material and hydrogen energy carrier.Aqueous electrocatalytic nitrogen reduction reaction(NRR),powered by renewable energy,has attracted tremendous interest during the past few years.Although some achievements have been revealed in aqueous NRR,significant challenges have also been identified.The activity and selectivity are fundamentally limited by nitrogen activation and competitive hydrogen evolution.This review focuses on the hurdles of nitrogen activation and delves into complementary strategies,including materials design and system optimization(reactor,electrolyte,and mediator).Then,it introduces advanced interdisciplinary technologies that have recently emerged for nitrogen activation using high-energy physics such as plasma and triboelectrification.With a better understanding of the corresponding reaction mechanisms in the coming years,these technologies have the potential to be extended in further applications.This review provides further insight into the reaction mechanisms of selectivity and stability of different reaction systems.We then recommend a rigorous and detailed protocol for investigating NRR performance and also highlight several potential research directions in this exciting field,coupling with advanced interdisciplinary applications,in situ/operando characterizations,and theoretical calculations.

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.

Brain-wide activation involved in 15 mA transcranial alternating current stimulation in patients with first-episode major depressive disorder

Background Although 15 mA transcranial alternating current stimulation(tACS)has a therapeutic effect on depression,the activations of brain structures in humans accounting for this tACS configuration remain largely unknown.Aims To investigate which intracranial brain structures are engaged in the tACS at 77.5 Hz and 15 mA,delivered via the forehead and the mastoid electrodes in the human brain.Methods Actual human head models were built using the magnetic resonance imagings of eight outpatient volunteers with drug-naïve,first-episode major depressive disorder and then used to perform the electric field distributions with SimNIBS software.Results The electric field distributions of the sagittal,coronal and axial planes showed that the bilateral frontal lobes,bilateral temporal lobes,hippocampus,cingulate,hypothalamus,thalamus,amygdala,cerebellum and brainstem were visibly stimulated by the 15 mA tACS procedure.Conclusions Brain-wide activation,including the cortex,subcortical structures,cerebellum and brainstem,is involved in the 15 mA tACS intervention for first-episode major depressive disorder.Our results indicate that the simultaneous involvement of multiple brain regions is a possible mechanism for its effectiveness in reducing depressive symptoms.