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The Ni-catalyzed reactions of benzamides with bicyclic alkenes were explored using DFT calculations.

We propose an intramolecular synergistic counteracting strategy of fluorescence resonance energy transfer and the inner filter effect for accurate photoactivation monitoring, to eliminate the influence of the biological microenvironment.

Metalloporphyrin- and phosphonium-functionalized porous organic polymers (POPs) were fabricated successfully via a post-synthesis modification strategy, which were demonstrated to be efficient heterogeneous catalysts for CO2 conversion.

The Ni-catalyzed reactions of benzamides with bicyclic alkenes were explored using DFT calculations. An unprecedented "N-H deprotonation circumvented" catalytic mechanism was proposed, over the more common N-H/C-H activation mechanism, in which (i) the circumvention of N-H deprotonation ensures the presence of N-H⋯O hydrogen bond interaction, thereby stabilizing the critical

Li-rich layered oxides with high capacity are expected to be the next generation of cathode materials. However, the irreversible and sluggish anionic redox reaction leads to the O2 loss in the surface as well as the capacity and voltage fading. In the present study, a simple gas-solid treatment with ferrous oxalate has been proposed to uniformly coat a thin spinel phase layer with oxygen vacancy and simultaneously realize Fe-ion substitution in the surface. The integration of oxygen vacancy and spinel phase suppresses irreversible O2 release, prevents electrolyte corrosion, and promotes Li-ion diffusion. In addition, the surface doping of Fe-ion can further stabilize the structure. Accordingly, the treated Feox-2 % cathode exhibits superior capacity retention of 86.4 % and 85.5 % at 1 C and 2 C to that (75.3 % and 75.0 %) of the pristine sample after 300 cycles, respectively. Then, the voltage fading is significantly suppressed to 0.0011 V per cycle at 2 C especially. The encouraging results may play a significant role in paving the practical application of Li-rich layered oxides cathode.

The continuous growth of the solid-electrolyte interface (SEI) and material crushing are the fundamental issues that hinder the application of Ge anodes in lithium-ion batteries. Solving Ge deformation crushing during discharge/charge cycles is challenging using conventional carbon coating modification methods. Due to the chemical stability and high melting point of carbon (3500 °C), Ge/carbon hybridization at the atomic level is challenging. By selecting a suitable carbon source and introducing an active medium, we have achieved the Ge/carbon doping at the atom-level, and this Ge/carbon anode shows excellent electrochemical performance. The reversible capacity is maintained at 1127 mAh g-1 after 1000 cycles (2 A g-1 (2-71 cycles), 4 A g-1 (72-1000 cycles)) with a retention of 84 % compared to the second cycle. The thickness of the SEI is only 17.4 nm after 1000 cycles. The excellent electrochemical performance and stable SEI fully reflect the application potential of this material.

Nickel-rich layered transition metal oxides are considered as promising cathode candidates to construct next-generation lithium-ion batteries to satisfy the demands of electrical vehicles, because of the high energy density, low cost, and environment friendliness. However, some problems related to rate capability, structure stability, and safety still hamper their commercial application. In this Review, beginning with the relationships between the physicochemical properties and electrochemical performance, the underlying mechanisms of the capacity/voltage fade and the unstable structure of Ni-rich cathodes are deeply analyzed. Furthermore, the recent research progress of Ni-rich oxide cathode materials through element doping, surface modification, and structure tuning are summarized. Finally, this review concludes by discussing new insights to expand the field of Ni-rich oxides and promote practical applications.

Recycling and reusing spent graphite have become urgent tasks, with massive numbers of lithium-ion batteries (LIBs) from hybrid electric vehicles (HEVs)/electric vehicles (EVs) retired every year. Meanwhile, interlayer designs based on carbon materials have attracted widespread attention to suppress the polysulfide shuttle effect in high-energy-density lithium–sulfur (Li–S) batteries. Nevertheless, designing simple and low-cost carbon-derived interlayers still remains a great challenge. Spent graphite possesses a porous structure, defects, and polar functional groups that were formed in situ, which can significantly confine polysulfides through a combination of physical and chemical adsorption. Meanwhile, transition metals introduced due to the dissolution of cathode active materials can also anchor polysulfides via S–TM bonding, as well as improving electrical conductivity and boosting polysulfide conversion kinetics. Herein, spent graphite recycled from waste LIBs was employed for the first time as a functional interlayer for Li–S batteries based on its intrinsic properties. The spent-graphite-derived interlayer exhibited remarkably enhanced trapping and catalytic performance toward polysulfides. A high discharge capacity of 968 mA h g−1 with a low decay rate of 0.08% per cycle over 500 cycles at 1 C can be obtained. The present work not only provides a promising strategy for the design of interlayers, but it also shows a high-value application of spent graphite.

Reducing the interfacial resistance between solid electrolytes and electrodes is critical for developing high-energy density solid-state batteries. In the present study, a simple strategy of designing an integrated cathode and solid electrolyte (ICSE) to avoid a contact interface is proposed and successfully fulfilled with the help of UV curving. Firstly, a porous polymer film (PVDF-HFP/PVDF) was formed on the surface of the porous LiFePO4 electrode via PVP dissolution. Secondly, curable monomers, including PEGDA/PETMP/TFEMA, were filled into the porous membrane via infiltration and concentration. Lastly, the ICSE was obtained via curing with ultraviolet light. The as-prepared LiFePO4//ICSE//Li solid battery displays excellent electrochemical performance with a high reversible capacity of 153 mA h g-1 and a capacity of over 140 mA h g-1 was retained after 150 cycles at 0.1C and 25 °C. This ICSE strategy may effectively contribute to the practical application of all-solid-state batteries.

Au(I)-catalyzed selective reactions of Et- and tBu-substituted propiolates (1a and 1a′) with 1,2-benzisoxazole(2a) provide a new strategy for purposefully access to desired bioactive heterocycles. ...

A palladium(II)-catalyzed direct 2-arylation of indoles by tetraarylstannanes with oxygen (balloon) as the oxidant at room temperature has been developed. Various tetraarylstannanes can be employed as aryl sources for 2-arylation of indoles in up to 89% yield, providing a practical and efficient catalytic protocol for accessing 2-arylindoles.

Iridium-catalyzed oxidative o-alkenylation of benzylamines with acrylates was enabled by the directing group pentafluorobenzoyl (PFB). Density functional theory calculations were performed to explore the detailed reaction mechanism. The calculated results reveal that N-deprotonation prior to C–H activation is favored over direct C–H activation. Moreover, C–H activation is reversible and not the rate-determining step, which has been supported by the experimental observation. The regio- and stereoselectivity of ethyl acrylate insertion are controlled by the steric effect and the carbon atom with a larger orbital coefficient of the π* antibonding orbital in the nucleophilic attack, respectively. The migratory insertion of ethyl acrylate is computationally found to be rate-determining for the whole catalytic cycle. Finally, the seven-membered ring intermediate IM11 undergoes a sequential N-protonation and β-H elimination with the assistance of AcOH, rather than β-H elimination and reductive elimination proposed experimentally, to afford the o-alkenylated product. IM11 is unable to directly cyclize through C–N reductive elimination because both sp3-hybridized N and C atoms are unfavorable for N–C reductive elimination. The origin of the directing group PFB preventing the product and intermediates undergoing aza-Michael addition has been explained.

The Ni(0)-catalyzed coupling of benzimidazole with 1,1-disubstituted allenes represents a new strategy for achieving controllable C–H allylations, alkenylations and dienylations. To understand the detailed mechanisms and origins of the switchable selectivities, density functional theory (DFT) calculations were conducted. The results using a tBu-substituted allene demonstrate that the formation of the allylated product involves a Ni-catalyzed C–H activation mechanism through ligand-to-ligand-hydrogen transfer (LLHT) under base-free conditions. In contrast, a Ni/NaOtBu co-promoted C–H activation mechanism is newly proposed in the presence of NaOtBu, which is remarkably different from the previously reported literature. The novel mechanism emphasizes that NaOtBu abstracts the Ni-activated heterocyclic (ipso-C)H atom followed by turnover limiting Ni slippage, and subsequently the allylated product is generated after alkene insertion and protonation. The strong electrostatic attraction between Ni and heterocyclic ipso-C in the Ni slippage pre-intermediate is critical for facilitating the Ni slippage. Once formed, the allylated product, assisted by NaOtBu, further evolves into a more stable alkenylated isomer. Employing a (tert-butyldimethylsilyl)-ether substituted allene as the substrate, the NaOtBu-induced chemoselectivity for dienylation vs. alkenylation was also probed and it was found that the O(tBu)–H⋯O(Si) hydrogen bonding interaction in the C–O(Si) cleavage pre-intermediate remarkably weakens the adjacent C–O(Si) σ-bond, thereby resulting in an exclusive C–O(Si) cleaved dienylation product. Further theoretical predictions suggest that the chemoselectivity might be reversed by replacing tBu in NaOtBu by the withdrawing C(CF3)3 group.

The mechanism of ruthenium-catalyzed [4 + 1] annulation of benzamide and propargyl alcohol has been investigated by density functional theory calculations. The reaction undergoes N–H and C–H deprotonations by a concerted metalation-deprotonation mechanism to afford a 5-membered ruthenacyclic species, which then undergoes ring expansion by alkyne insertion to deliver a 7-membered ring intermediate. Our study focused on how the successive hydrogen migrations take place that remains unclear. The 1,2-proton migration and 1,3-proton transfer from O to C are successively finished by using acetate anion as a shuttle (a stepwise process). In contrast to the experimental proposal that the reaction experiences a Ru(II)–Ru(0)–Ru(II) transformation, our study unveiled a Ru(II)–Ru(IV)–Ru(II) transformation in the reaction. In addition, our calculations suggested that the EtO–N bond cleavage rather than the C–H activation is likely to be the rate-determining step for the entire reaction, which is not in contradiction w...

The unexpected oxyamination reaction of O, ω-unsaturated alkoxyamines was found experimentally. The mechanistic issues were studied by DFT calculations. It is suggested that the reaction undergoes [3 + 2] cyclic addition, O N bond cleavage, C N reductive elimination, and the Rh N unit protonation, generating the product and regenerating the active catalyst. The nitrene Rh(V) species containing a Rh C bond rather than a Rh O bond was suggested to be involved in the reaction mechanism. Why the substrate A with X = O but not X = C undergoes oxyamination reaction was rationalized based on the suggested reaction mechanism.

The gold(iii)-catalyzed annulations of alkynes with anthranils were evaluated using DFT calculations. A unified rationale for the Br-migration on α-imino gold(iii)-carbene was proposed, from which an unprecedented "N-donation/abstraction substitution" mechanism was established using the substituted anthranils, while direct C-H nucleophilic attack was involved with the unsubstituted anthranils. The controlling factors guiding the site-selectivity were uncovered. These computational studies provide insight for developing new α-imino gold(iii)-carbene mediated reactions.

Density functional theory (DFT) calculations have been performed to unravel the detailed mechanism of the CpRe(CO)3-catalyzed coupling reaction of CO2 with chloromethyloxirane (R). The mechanisms proposed in previous literature have been examined. However, the computed results seem not to completely rationalize the experimental findings. Alternatively, by performing an exhaustive search on the potential energy surface, we presented a novel CO-assisted mechanism, which provides an effective access to the catalytic coupling. The newly established mechanism involves the C O bond cleavage of R from the less hindered side, release of one CO ligand, CO2 insertion, re-coordination of the dissociated CO ligand, another CO ligand shift, reductive elimination with simultaneous migration of carbonyl substituent, resulting in P and regeneration of CpRe(CO)2. Two CO ligands attached to CpRe(CO)2 play significant roles in lowering the key CO2 insertion and reductive elimination: (i) One CO ligand dissociation prior to CO2 insertion contributes to reduce the electron density on the Re metal, facilitating the CO2 O atom nucleophilic attack. (ii) After performing the migration, another initially inactive CO ligand serves as a carbonyl substituent, which lowers the energy penalty for later reductive elimination through the resultant extra π-interaction and the smaller ring tension energy involved in TS. The theoretical results provide insight into the mechanism of the important coupling reaction and rationalize well the experimental observations.

Density functional theory (DFT) calculations have been performed to study the Pd-catalyzed C-H functionalization of (E)-N-methoxy cinnamamide (E1), which selectively provides the α-C-H activation products (EP as minor product and its C═C rotation isomer ZP' as major product). Three crucial issues are solved: (i) The detailed mechanism leading to ZP' is one issue. The computational analyses of the mechanisms proposed in previously experimental and theoretical literature do not seem to be consistent with the experimental findings due to the high barriers involved. Alternatively, we present a novel oxidation/reduction-promoted mechanism featuring the Pd(0) → Pd(II) → Pd(0) transformation. The newly proposed mechanism involves the initial coordination of the active catalyst PdL2 (L = t-BuCN) with the C═C bond in EP, followed by the oxidative cyclization/reductive decyclization-assisted C═C double-bond rotation processes resulting in ZP' and regeneration of PdL2. (ii) The origin of the product E/Z selectivity is the second issue. On the basis of the calculated results, it is found that, at the initial stage of the reaction, EP is certainly completely generated, while no ZP' formation occurred. Once E1 is used up, EP immediately acts as the partner of the new catalytic cycle and sluggishly evolves into ZP'. A small amount of generated ZP' would reversibly transform to EP due to the higher barrier involved. (iii) The intrinsic reasons for the regioselectivity are the third issue. The calculated results indicate that the regioselectivity for α-C-H activation is mainly attributed to the stronger electrostatic attraction between the α-C and the metal center.

Density functional theory (DFT) calculations have been conducted to unravel the mechanisms and chemoselectivities of Au-catalyzed diazo-based couplings with phenyl unsaturated aliphatic alcohols: the propargyl alcohol Ba resulting in the [4 + 1]-cycloaddition product P4a and the allyl alcohol Db giving the [2,3]-σ rearrangement species P5b. P4a formation involves a catalyst interaction with phenyldiazoacetate, N2 release, a hydroxyl O nucleophilic attack of Ba, a [1,4]-H shift, coordination isomerization, 5-endo-dig cyclization, a [4,1]-H shift and a H2O-assisted [1,3]-H shift. After the [4,1]-H shift, the slightly less favorable five-membered ring-opening possibly follows to afford trace P5a ([2,3]-σ rearrangement product), which would be kept in solution due to subsequent irreversible evolution. In addition, the Ba-involved chemoselectivity was probed and explained as follows: (i) both large H(hydroxyl)⋯C(carbene) electrostatic repulsion and strong three-membered ring strain involved in the TS make the formation of the O–H insertion product P1a difficult and (ii) the nucleophilic attack from the C2 atom of Ba brings about a structural twisting and thus increases the energy penalty forming the cyclopropenation product P2a. On the other hand, compared with the sp-C2 atom of Ba, the sp2-C2 atom of Db greatly facilitates the five-membered ring-opening step because of the presence of an extra pπ–pπ orbital overlap and eventually provides P5b exclusively.

High catalytic performance of a single-atom transition metal ion (TMx+) anchored on the two-dimensional (2D) C2N lattice is predicted for HCOOH dehydrogenation. Considering the Co2+, Cu2+ and Ni2+ non-noble metal ions supported by C2N, we use density functional theory to demonstrate dehydrogenation energy barriers as low as those for pure Pt and Pd catalysts. The high catalytic performance is ascribed to the reaction occurring through a dual-active center composed of TMx+ and a nearby N atom of C2N. Specifically, C2N–Co2+ in the low spin state (S = 1/2) greatly promotes HCOOH dehydrogenation by decreasing the barrier of the rate-determining step to only 0.30 eV, mainly due to the strong ability of TMx+ to extract charges from HCOOH and C2N. The obtained mechanistic insights help the rational design of single-atom based transition metal ion catalysts supported by 2D materials.

The mechanisms and chemo- and regioselectivities of divergent (Ni(cod)2/PCy3)-mediated/-catalyzed C(sp3)–F bond activation of 2-trifluoromethyl-1-alkenes (1) with alkynes (2) were investigated by density functional theory (DFT) calculations. The nickel-mediated/-catalyzed reaction involves sequential ligand exchange, alkene coordination, oxidative cyclization (1 + Ni(0) + 2), and first β-F(C(sp3)) elimination to give a common and requisite alkenylnickel(II) species, which bifurcates into either stoichiometric defluorinative [3 + 2] cycloaddition product 3 or catalytic defluorinative coupling products (nonmethylated 5, monomethylated 8, or trimethylated 9) depending on the absence and presence of additional reagents (Et3SiH, ZnMe2, and AlMe3). The Et3SiH-induced formation of 5 is found to be a result of facile metathesis relative to the 5-endo insertion leading to 3. Because of the presence of an F→Zn/Al interaction, ZnMe2/AlMe3 brings the methyl into defluorinative coupling products. In the stoichiometric...

A fabrication strategy for biphasic gels is reported, which incorporates high-internal-phase emulsions. Closely packed micro-inclusions within the elastic hydrogel matrix greatly improve the mechanical properties of the materials. The materials exhibit excellent switchable mechanics and shape-memory performance because of the switchable micro- inclusions that are incorporated into the hydrogel matrix. The produced materials demonstrated a self-healing capacity that originates from the noncovalent effect of the biphasic heteronetwork. The aforementioned characteristics suggest that the biphasic gels may serve as ideal composite gel materials with validity in a variety of applications, such as soft actuators, flexible devices, and biological materials.

Benzene ring functionalization provides useful alternatives to access indole derivatives and has received much attention in recent years. In this work, the mechanism of Pt(II)-catalyzed cyclization/alkynylation of benziodoxole with pyrrole homopropargylic ethers to generate C5-alkenylated indole derivatives has been studied with the aid of density functional theory (DFT) calculations. We found that five-membered-ring cyclization/six-membered-ring cyclization is competitive in the formation of an indole skeleton. The following aromatization stage prefers the reaction sequence bicarbonate-assisted deprotonation at the C3a position, H2CO3-promoted methoxy elimination at the C7 position, and bicarbonate-assisted deprotonation at the C6 position. In the last alkynylation stage, the oxidative substitution mechanism assisted by H2CO3 is found to be favored over the previously proposed 1,2-iodo shift and oxidative addition. The overall rate-determining step is oxidative substitution. Additionally, an interesting ...

Density functional theory (DFT) calculations have been performed to unravel the mechanism of Lewis-acid-induced Ni(cod)2-catalyzed selective coupling reactions of one diketene and two alkynes. Complex mixtures (unsymmetrical phenylacetic acid P1, symmetrical phenylacetic acid P2 and (3E)-4-ethyl-5-methylene-3-heptenoic acid P3) were obtained in the absence of Et2Al(OEt). P1 formation involves C(sp2)-O oxidative addition of diketene, twice alkyne insertion, intramolecular C═C insertion, acidolysis, and β-H elimination. For P2/P3 formation, the common key issue related to the C═C double bond cleavage of the substrate diketene was explored and found that it was accomplished via a four-membered-ring-closure/four-membered-ring-opening process. And then, P2 was produced via the second alkyne insertion while P3 was accessed by a stoichiometric reaction with HCl. The Et2Al(OEt)-induced chemoselectivity was also probed. It is found that the Ni–O (from Al reagent) bonding facilitates the second alkyne insertion, an...

Terminal alkenes were selectively cleaved into ketones and aldehydes catalyzed by a binuclear copper catalyst bearing a simple salicylate ligand with O2 as the oxidant. The reaction was carried out under an atmosphere of O2 (balloon) with 0.5 mol% of catalyst and could be performed on a gram scale, providing a convenient and practical method for the cleavage of terminal alkenes into carbonyl compounds.

We report on a dual ratiometric two-photon fluorescent probe for in situ sensing of mitochondrial CE activity and pH. Using the probe it is possible to visualize the CE-mediated acidification of hepatoma cells and hepatic tissues during medication with antipyretic anti-inflammatory drugs.

Gold-catalyzed cyclization of 2-alkynyl-N-propargylanilines provides a step-economic method for the construction of three-dimensional indolines. In this article, the M06 functional of density functional theory was employed to gain deeper insights into the reaction mechanism and the associated intriguing experimental observations. The reaction was found to first undergo Au(I)-induced cyclization to form an indole intermediate, 1,3-propargyl migration, and substitution with the substrate 2-alkynyl-N-propargylaniline (R1) to generate the intermediate product P1, an allene species. Subsequently, Au(I)-catalyzed conversion of P1 into the final product P2, an indoline compound, occurs first through direct cyclization rather than via the previously proposed four-membered carbocycle intermediate. Thereafter, water-assisted oxygen heterocycle formation and proton transfer generate the final product. The calculated activation free energies indicate that P1 formation is 5.9 times slower than P2 formation, in accordance with the fact that P1 formation is rate-limiting. Futhermore, the intriguing experimental phenomenon that P2 can be accessed only after almost all the substrate R1 converts to P1 although P1 formation is rate-limiting was rationalized by employing an energetic span model. We found the initial facile cyclization to form a highly stable indole intermediate in the formation of P1 is the key to the intriguing experimental phenomenon.

With the aid of density functional theory (DFT) calculations, the Pd-catalyzed reactions of aryl iodide with unsymmetrical alkyne leading to two products containing C(sp 3 )−I bond ( P3 and P4 ) and one product containing a three-membered carbocyclic unit ( P5 ), have been studied theoretically. It is found that both the alkyne insertion and the subsequent C C bond insertion involved in the reaction are the major thermodynamic driving forces. The alkyne insertion instead of the C(sp 3 )−I reductive elimination is predicted to be rate-determinant. Similar barrier heights calculated for the two insertion modes of unsymmetrical internal alkyne ( TS 3-4 and TS 3′-4′ ) lead to the products P3 (47.2%) and P4 + P5 (48.8%) having similar product yields. The intriguing formation of the product containing a three-membered carbocyclic unit ( P5 ) was investigated in details. The second alkene insertion is found to be kinetically more favored than the C(sp 3 )−I reductive elimination, leading to product P5 (39.0%) more productive than P4 (9.8%). The remarkably thermodynamically favored β−H elimination is the key factor enabling formation of P5 . Why significant bulky phosphine ligand such as P(t-Bu) 3 instead of small one such as P(Me) 3 was employed experimentally have also been rationalized based on our calculation results.

Pd-catalyzed decarboxylative Heck-type coupling of 3-chlorobenzo[b]thiophene-2-carboxylic acids with styrenes have been developed as an efficient strategy for the construction of functionalized benzo[b]thiophenes. Theoretical analysis shows that AgCl generated during the reaction, instead of Pd, π-coordinates with the carboxyl O atom, making easy the rate-determining CO2 dissociation. The divergent reactivities of the Cl-substituted and H-substituted 3-benzo[b]thiophene-2-carboxylic acids are mainly due to the presence of the Cl substituent, which reduces the adjacent π-π interplay, thereby significantly contributing to decarboxylation. Therefore, the presence of both AgCl and the Cl substituent are of key importance in ensuring the occurrence of the reaction under the given conditions.

The reaction features combination of C H activation and ring opening of cyclopropanol was studied with the aid of DFT calculations. With the reaction of N-pyrimidylindoline and 1-benzylcyclopropanol as an example to accomplish the alkylation, we found the order of C H activation/ring opening is difficult to occur. Instead, the order of ring opening/C H activation is predicted to be more reasonable, which circumvents the N→Rh bond breaking. Two catalytic cycles were suggested. The first cycle relates to the catalytic oxidation of cyclopropanol by Cu(II) to generate an intermediate product, the vinyl ketone. The mechanism mainly involves prior ring opening of cyclopropanol and β-H elimination. The second cycle relates to the product formation from the resultant intermediate product, in which the C H activation of N-pyrimidylindoline, C C bond insertion of the intermediate product and protonation are included. The insights gained in this study are expected to be pertinent in other reaction systems involving combination of C H activation and ring opening.

A theoretical and computational study was performed on the nitrene-participating three-component carboamination of dienes. The reaction proceeds mainly through C–H activation, olefin insertion, metal nitrenoid formation, and selective C N coupling. The role of solvent effect enables the extrusion of carbon dioxide to generate the key metal nitrenoid being not concerted but stepwise. The Rh = N was indicated by HOMO-LUMO interactions that the backdonation is dominant and hence showing the electron withdrawing behavior of nitrene. Regioselectivity for C C bond formation, E-type product, and 1,4-carboamination was discussed.

Density functional theory (DFT) calculations were used to explore the Au(I)-catalyzed selective [4 + 1] annulations of cyclopropyl- and H-substituted 1,4-diyn-3-ols with isoxazole. The results indicated that after the N-nucleophilic attack of isoxazole, instead of obtaining the α–hydroxy gold carbene intermediate proposed experimentally, a concerted three-step forward product by isoxazole O[sbnd]N cleavage, 1,2-phenylalkyne shift and the hydroxyl H shift was identified as the key intermediate, for the reaction proceeding either via an Au-assisted C[dbnd]C double-bond rotation to produce the Z-isomeric enone or via two different Au-assisted C[dbnd]C rotations to furnish the E-configured enone depending on the substituents used. Further theoretical investigations indicated that the chemoselective step is the nucleophilic cyclization but not the C[dbnd]C double-bond rotation. The chemoselective preference for the Z-configured product using the cyclopropyl substitutent was attributed to two factors: i) the additional O[tbnd]H[sbnd]N hydrogen bonding interaction stabilizes the rate-determining cyclization TS leading to the Z-product, and ii) further Z-E product-isomerization is blocked due to significant structural deformation being involved. In contrast, using the H substituent results in a reversed chemoselectivity with exclusive formation of the E-configured enone, which is closely related to the smaller entropy effects involved.

By carrying out density functional theoretical calculations, we have performed a detailed mechanistic study of the Au(I)-catalyzed cycloisomerization of 1,6-enylnyl ester in a dry and wet dichloromethane solvent corresponding to hydrogenation and hydrolysis processes, respectively. The hydrogenation and hydrolysis mechanisms proposed in the previous literature starting from an enol ketal intermediate without the involvement of an Au(I) catalyst are found to involve high barriers and thus contradict the observed experimental findings. Alternatively, based on the theoretical calculations, a novel hydrogenation mechanism (i.e., Au-induced H-shift followed by enol intermediate self-promoted H-shift) and a hydrolysis mechanism (i.e., Au-stabilized H-shift/C-O binding with subsequent H2O-assisted H-shift) from an Au-enol ketal adduct corroborate the experimental observations. The calculated results indicate that under unchanged wet conditions, the formation of a hydrolysis product is not involved in the intermediacy of the hydrogenation product. However, if the initial dry environment is provided, a hydrogenation product will be afforded. And then it will relentlessly evolve into a hydrolysis product in the subsequent wet conditions. The present theoretical results not only rationalize the experimental observations well but provide new insight into the mechanisms of the significant water-mediated cycloisomerization reaction.

N-Aryl tetrahydroisoquinolines were oxidised to dihydroisoquinolones through the relay catalysis of a binuclear paddle-wheel copper complex and a vitamin B1 analogue with oxygen as oxidant. Mechanistic studies revealed that the copper catalyst oxidises amines to the corresponding iminium salts, which are then oxygenated to lactam products by catalysis of the vitamin B1 analogue.

The reaction mechanism for the palladium(II)-catalyzed cross-coupling of N-tosyl hydrazone S1 with alkene S2 has been studied with the help of density functional calculations. The acetate present in the catalyst was found to directly participate in the reaction. The tBuO– group that was added in excess into the reaction system plays an important role in forming the new C═C double bond. In addition, we clarified how water plays an assisting role to promote the catalytic reaction studied.

Reaction mechanisms of the Ni(COD)(2)-catalyzed [2 + 2 + 2] cycloaddition of unsymmetric diynes and CO2 have been theoretically studied by using the density functional theory calculations. Three major steps are included, oxidative coupling of CO2 with Et-substituted C=C bond, the second C=C bond insertion and reductive elimination of the product from the Ni center, in which the C=C bond insertion was found to be rate-determinant. The steric arrangement of the N,P-bidentate ligand was demonstrated to be influential on reaction barriers. Based on the mechanistic study, the regioselectivity of the catalytic reaction was elucidated. In addition, we also explained why the mechanisms involving oxidative coupling of both the C=C bonds are unavailable. (C) 2014 Elsevier B.V. All rights reserved.

The Pd-catalyzed reactions of α-diazocarbonyl compounds with allylic esters have been comprehensively studied with the aid of DFT calculations. The reaction can be divided into two catalytic processes. The first process is Pd-catalyzed allylic ester decarboxylation leading to formation of the intermediate product 1,4-enyne (P1). In this process, the ester oxidative addition proceeds via an ion-pair mechanism rather than a concerted mechanism. The decarboxylative step from the oxidative addition product (4) proceeds via an (η2-C≡C)→Pd-coordinated ion-pair intermediate (9). The rate-determining step for this catalytic process is found to be the 1,4-enyne reductive elimination step. The second process is the Pd-catalyzed reaction between 1,4-enyne (P1) and the diazo substrate, leading to the final product. In this process, the coupling between 1,4-enyne (P1) and the metal carbene generated from the reaction of PdL2 with the diazo substrate forms a four-membered metallacyclic intermediate, from which β-phenyl...

Pd-catalyzed decarboxylative Heck-type coupling of 3-chlorobenzo[b]thiophene-2-carboxylic acids with styrenes have been developed as an efficient strategy for the construction of functionalized benzo[b]thiophenes. Theoretical analysis shows that AgCl generated during the reaction, instead of Pd, π-coordinates with the carboxyl O atom, making easy the rate-determining CO2 dissociation. The divergent reactivities of the Cl-substituted and H-substituted 3-benzo[b]thiophene-2-carboxylic acids are mainly due to the presence of the Cl substituent, which reduces the adjacent π–π interplay, thereby significantly contributing to decarboxylation. Therefore, the presence of both AgCl and the Cl substituent are of key importance in ensuring the occurrence of the reaction under the given conditions.

The Au-catalyzed [2 + 2 + 2] cycloadditions of ynamides with two discrete nitriles were theoretically studied with the aid of DFT calculations. The reaction under consideration is found to start from binding of the catalyst with the ynamide rather than with the nitrile. The Au(I)–ynamide species (1) can effectively induce dimerization of two nitrile molecules while the catalyst only cannot. The Au(I)–ynamide species (1) is revealed to be more reactive than the Au(I)–nitrile species (2). Also, the regioselectivity and the influence of EWG vs. EDG involved in the reaction were also rationalized.

With the aid of DFT calculations, the FeBr3-catalyzed skeletal rearrangements of 2-cyclohexanal,2-p-C6H4OMe-propylaldehyde (1A) and 2-phenyl,2-p-C6H4OMe-propylaldehyde (1B) were investigated theoretically. As compared to mono-FeBr3 as a catalyst, the bis-FeBr3 serving as a catalyst is found to be not only enhancing the catalytic efficiency but also improving the product selectivity. For the reaction starting from 1A, the [1,2]-group shift (first step) is rate-determining, and why the Cy shift is the most favored is rationalized in comparison with the p-C6H4OMe and Me shifts. For the reaction starting from 1B, the [1,2]-H shift (second step) is rate-determining although the [1,2]-p-C6H4OMe shift is favored over the [1,2]-phenyl shift. In contrast to the experimental proposal, the newly established H2O/Br(-) joint-assisted H-shift mechanism explains the partial α-H source of the [1,2]-Cy shift product. In addition, we discussed the inherent mechanism that explains why both the [1,2]-p-C6H4OMe and [1,2]-p-C6H4CF3 shifts are more facile than the [1,2]-phenyl shift although the substituents -OMe and -CF3 have opposite electronic behaviors.

An effective room-temperature Stille cross-coupling of aryl ureas with tetraarylstannanes via palladium-catalyzed C–H bond activation is reported, providing a mild method for direct arylation of aromatic C–H bonds.

By carrying out density functional theory (DFT) calculations, we have performed a detailed mechanism study on the Pt(II)-catalyzed [3+2] cycloaddition reactions of two propargyl ether derivatives, 2-(3-methoxyprop-1-ynyl) aniline derivative ( 1A ) and phenol derivative ( 2A ), with n -butyl vinyl ether. The calculated results show that the two reactions proceed according to similar elementary step mechanism. For both the two reactions, the elimination of the methoxy group is the rate-determining step. The present results provide a theoretical validation for the mechanism proposed by Iwasawa et al.

To understand the mechanism of allene formation through the rearrangement of cyclopropenes catalyzed by PtCl2, we have performed a detailed density functional theory calculation study on a representative substrate, 1-(trimethylsilyl)-2-(phenylethyl)cyclopropene. Three reaction pathways proposed in the original study have been examined; however the calculated results seem not to completely rationalize the experimental findings. Alternatively, by performing an exhaustive search on the potential energy surface, we present a novel mechanism of PtCl2, which is fixed appropriately on the cyclopropene/allene to form the linear Cl–Pt–Cl disposition, a vital configuration for catalyzing the rearrangement of cyclopropene. The newly proposed mechanism involves an SN2-type C–C bond activation of the cyclopropene by PtCl2 fixed on a cyclopropene molecule via the d−π interaction between the metal center and the substrate to form the product precursor PtCl2-allene with the metal center coordinated to the external C═C bo...

By performing density functional theory calculations, we have studied the CO pathway and non-CO pathway of methanol oxidation on the PtAu(111) bimetallic surface. CO is shown to possess larger adsorption energy on the PtAu(111) surface than that on the pure Pt(111) surface, and the non-CO pathway on the bimetallic surface is found to be energetically more favorable than the CO pathway. These calculated results propose that the improved electrocatalytic activity of PtAu bimetallic catalysts for methanol oxidation should be attributed to the alternation in the major reaction pathway from the CO pathway on the pure Pt surface to the non-CO pathway on the PtAu bimetallic surface rather than the easier removal of CO on PtAu catalysts than on pure Pt catalysts.

By carrying out density functional theory calculations, we have performed a detailed mechanism study for the cycloisomerization reaction of 4-phenyl-hexa-1,5-enyne catalyzed by homogeneous gold to better understand the observed different catalytic activity of several catalysts, including (PPh(3))AuBF(4), (PPh(3))AuCl, AuCl(3), and AuCl. In all situations, the reaction is found to involve two major steps: the initial nucleophilic addition of the alkynyl onto the alkene group and the subsequent 1,2-H migration. It is found that the potential energy surface profiles of systems are very different when different catalysts are used. For (PMe(3))AuBF(4)- and (PMe(3))AuCl-mediated systems, the nucleophilic addition is the rate-determining step, and the calculated free energy barriers are 15.2 and 41.9 kcal/mol, respectively. In contrast, for AuCl(3)- and AuCl-mediated systems, the reactions are controlled by the dissociations of catalysts from the product-like intermediates, and the calculated dissociation energies are 18.1 and 21.7 kcal/mol, respectively, which are larger than both the corresponding free energy barriers of the nucleophilic addition and the H-migration processes (8.5 and 7.3 kcal/mol for the AuCl(3)-mediated reaction, and 16.9 and 11.3 kcal/mol for the AuCl-mediated reaction). These results can rationalize the early experimental observations that the reactant conversion rates are 100, 0, and 50% when using (PPh(3))AuBF(4), (PPh(3))AuCl, and AuCl(3) as catalysts, respectively. The present study indicates that both the ligand and counterion of homogeneous Au catalysts importantly influence their catalytic activities, whereas the oxidation state of Au is not a crucial factor controlling the reactivity.