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For decades, N2 activation and functionalization have required the use of transition metal complexes. Thus, it is one of the most challenging projects to activate the abundant dinitrogen through metal‐free systems under mild conditions. Here, we demonstrate a proof‐of‐concept study on the catalytic hydrogenation of dinitrogen (with activation energy as low as 15.3 kcal mol−1) initiated by a dual Lewis acid (DLA) via density functional theory (DFT) calculations. In addition, such a DLA could be also used to activate a series of small molecules including carbon dioxide, formaldehyde, N‐ethylenemethylamine, and acetonitrile. It is found that aromaticity plays an important role in stabilizing intermediates and products. Our findings provide an alternative approach to N2 activation and functionalization, highlighting a great potential of DLA for small molecule activation. [ABSTRACT FROM AUTHOR]

As the strongest triple bond in nature, the N≡N triple bond activation has always been a challenging project in chemistry. On the other hand, since the award of the Nobel Prize in Chemistry in 1950, the Diels‐Alder reaction has served as a powerful and widely applied tool in the synthesis of natural products and new materials. However, the application of the Diels‐Alder reaction to dinitrogen activation remains less developed. Here we first demonstrate that a transition‐metal‐involved [4+2] Diels‐Alder cycloaddition reaction could be used to activate dinitrogen without an additional reductant by density functional theory calculations. Further study reveals that such a dinitrogen activation by 1‐metalla‐1,3‐dienes screened out from a series of transition metal complexes (38 species) according to the effects of metal center, ligand, and substituents can become favorable both thermodynamically (with an exergonicity of 28.2 kcal mol−1) and kinetically (with an activation energy as low as 13.8 kcal mol−1). Our findings highlight an important application of the Diels‐Alder reaction in dinitrogen activation, inviting experimental chemists' verification. [ABSTRACT FROM AUTHOR]

Molecular nitrogen (N2) is abundant in the atmosphere and, found in many biomolecules, an essential element of life. The Haber–Bosch process, developed over 100 years ago, requires relatively harsh conditions to activate N2 on the iron surface and generate ammonia for use as fertilizer or to produce other chemicals, leading to consumption of more than 2 % of the world's annual energy supply. Thus, developing "green" approaches for N2 activation under mild conditions is particularly important and urgent. Here we demonstrate that a metal‐free N2 activation could be favorable both thermodynamically and kinetically (with an activation energy as low as 9.1 kcal mol−1) by using a carbon‐boron formal frustrated Lewis pair, which is supported by high‐level coupled cluster calculations. Mechanistic studies reveal that aromaticity plays a crucial role in stabilizing both the transition state and the product. Our findings highlight the importance of a combination of an N‐heterocyclic carbene with a methyleneborane unit in metal‐free N2 activation, providing conceptual guidance for experimental realization. [ABSTRACT FROM AUTHOR]

Dinitrogen (N2) activation is particularly challenging under ambient conditions because of its large highest occupied molecular orbital‐lowest unoccupied molecular orbital (HOMO‐LUMO) gap (10.8 eV) and high bond dissociation energy (945 kJ mol−1) of the N≡N triple bond, attracting considerable attention from both experimental and theoretical chemists. However, most effort has focused on metallic systems. In contrast, nitrogen activation by frustrated Lewis pairs (FLPs) has been initiated recently via theoretical calculations. Here we perform density functional theory (DFT) calculations to screen a series of experimentally viable FLPs for small‐molecule activation including N2, O2, CO, CO2, CS2, H2O and CH4. In addition, aromaticity is found to play an important role in most of these small‐molecule activation. The particularly thermodynamic stabilities of the activation products and low reaction barriers could be a step forward for the development of FLP towards small‐molecule activation including N2, inviting experimental chemists' verification. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculations were carried out to investigate the 1,2-migration in metallasilabenzenes. The results suggested that the chloride migration of metallabenzenes is unfavorable due to the loss of aromaticity in the nonaromatic analogues. In sharp contrast, such a migration in metallasilabenzenes is favorable due to the reluctance of silicon to participate in π bonding. The migration of hydride and methyl group from the metal center to the silicon atom in metallasilabenzenes is computed to be also feasible. In addition, the π donor ligand and the third row transition metal can stabilize metallasilabenzenes. Thus, such a migration becomes less favorable thermodynamically and kinetically. These findings could be very helpful for synthetic chemists to realize the first metallasilabenzene. [ABSTRACT FROM AUTHOR]

CO2 capture has attracted increasing attention owing to its contribution to global warming and climate change as a greenhouse gas. As an alternative strategy to transition-metal-based chemistry and , frustrated Lewis pairs have been developed to sequester CO2 efficiently under mild conditions. However, the mechanism of CO2 sequestration with amidophosphoranes remains unclear. Herein, we present a thorough density functional theory study on a series of amidophosphoranes. Our results reveal that the interplay of the ring strain and the trans influence determines the reactivities, thus opening a new avenue to the design of frustrated Lewis pairs for CO2 capture. [ABSTRACT FROM AUTHOR]

Based on Hückel's and Baird's rules, species are aromatic either in the lowest singlet state (S0) or the lowest triplet state (T1) only. Thus, species with adaptive aromaticity (with aromaticity in both the S0 and T1 states) is particularly rare. On the other hand, σ‐aromaticity in the T1 state has been underdeveloped, let alone adaptive σ‐aromaticity. Herein, via various aromaticity indices including NICS, ACID and EDDB, we demonstrate adaptive σ‐aromaticity in an unsaturated three‐membered ring, which is a traditional area dominated by π‐aromaticity. The origin of adaptive σ‐aromaticity could be attributed to the excitation mode of the T1 state formed from out‐of‐plane π molecular orbital to the π* orbitals. Thus the σ‐aromaticity of the three‐membered ring in the S0 state could hold in the T1 state. Our findings extend the concept of adaptive σ‐aromaticity into three‐membered rings and could be useful to further develop the concept of both σ‐aromaticity and adaptive aromaticity. [ABSTRACT FROM AUTHOR]

Discovery of species with adaptive aromaticity (being aromatic in both the lowest singlet and triplet states) is particularly challenging as cyclic species are generally aromatic either in the ground state or in the excited state only, according to Hückel's and Baird's rules. Inspired by the recent realization of cyclo[18]carbon, here we demonstrate that cyclo[10]carbon possesses adaptive aromaticity by screening cyclo[n]carbon (n=8−24), which is supported by nucleus‐independent chemical shift (NICS), anisotropy of the current‐induced density (ACID), π contribution of electron localization function (ELFπ) and electron density of delocalized bonds (EDDB) analyses. Further study reveals that the lowest triplet state of cyclo[10]carbon is formed by in‐plane ππ* excitation. Thus, the major contribution to the aromaticity from out‐of‐plane π molecular orbitals does not change significantly in the lowest singlet state. Our findings highlight a crucial role of out‐of‐plane π orbitals in maintaining aromaticity for both the lowest singlet and triplet states as well as the aromaticity dependence on the number of the carbon in cyclo[n]carbon. [ABSTRACT FROM AUTHOR]

Transfer hydrogenation of azobenzene with ammonia borane mediated by pincer bismuth complex 1 was systematically investigated through density functional theory calculations. An unusual metal‐ligand cooperation mechanism was disclosed, in which the saturation/regeneration of the C=N functional group on the pincer ligand plays an essential role. The reaction is initiated by the hydrogenation of the C=N bond (saturation) with ammonia borane to afford 3CN, which is the rate‐determining step with Gibbs energy barrier (ΔG≠) and Gibbs reaction energy (ΔG) of 25.6 and −7.3 kcal/mol, respectively. 3CN is then converted to a Bi−H intermediate through a water‐bridged pathway, which is followed up with the transfer hydrogenation of azobenzene to produce the final product N,N′‐diphenylhydrazine and regenerate the catalyst. Finally, the catalyst could be improved by substituting the phenyl group for the tert‐butyl group on the pincer ligand, where the ΔG≠ value (rate‐determining step) decreases to 24.0 kcal/mol. [ABSTRACT FROM AUTHOR]

The BN-doped organic analogues are interesting as aliphatic amineboranes for hydrogen storage, precursors for aromatic borazines and adsorbent cage azaboranes. However, BN-doped aliphatic polyenes remained undeveloped. Herein, we perform theoretical calculations on two mono BN-doped aliphatic lower polyenes, 1,3-butadiene and 1,3,5-hexatriene. A general rule is proposed, i.e., isomers with terminal nitrogen and directly BN-connected, N−B(R), in particular, are of significant thermodynamic stability as compared with their inverse analogues (where boron is at the terminal position). The N−B(R) type isomers are found to be the most stable ones in both polyenes. Isomers with terminal B and N are of intermediate stability. Highly destabilized isomers are those with one terminal methylene group and one terminal heteroatom in the butadiene series, and two terminal methylene groups in the hexatriene series. Rules established here may lead researchers to synthesize isomers with particular thermodynamic stability. [ABSTRACT FROM AUTHOR]

Dinitrogen (N2) activation is particularly challenging due to the significantly strong N≡N bond, let alone the catenation of two N2 molecules. Recent experimental study shows that cyclic (alkyl)(amino)carbene (CAAC)‐stabilized borylenes are able to tackle N2 activation and coupling below room temperature. Here we carry out density functional theory calculations to explore the corresponding reaction mechanisms. The results indicate that the reaction barrier for the dinitrogen activation by the first borylene is slightly higher than that by the second borylene. In addition, replacing the CAAC moiety of the borylenes with cyclic diaminocarbenes (CDACs) could make such dinitrogen activation and coupling more favorable thermodynamically. The reaction mechanisms of the intramolecular C−H bond activation of borylene have also been discussed, which is found to be favorable both thermodynamically and kinetically in comparison with N2 activation. Thus, adequate attention should be paid to the design of borylenes aiming at N2 activation. In addition, our calculations suggest that the CDAC moiety of the borylene could lead to a different product in terms of intramolecular C−H bond activation. All these findings could be useful for the development of dinitrogen activation as well as C−H bond activation by main group species. [ABSTRACT FROM AUTHOR]

Aromaticity, one of the most important concepts in organic chemistry, has attracted considerable interest from both experimentalists and theoreticians. It remains unclear which NICS index is best to evaluate the triplet-state aromaticity. Here, we carry out thorough density functional theory (DFT) calculations to examine this issue. Our results indicate that among the various computationally available NICS indices, NICS(1) zz is the best for the triplet state. The correlations can be improved from 0.840 to 0.938 when only neutral species are considered, demonstrating the significant effect of the charge on the triplet-state aromaticity. In addition, calculations suggest that five-membered cyclic species with 'hyperconjugative' aromaticity (and antiaromaticity) in the S0 state will become antiaromatic (and aromatic) in the T1 state, indicating an important role of hyperconjugation. Finally, a moderate correlation (r2=0.708) is identified between the NICS(1) zz values and spin distributions. [ABSTRACT FROM AUTHOR]

Due to consumption of more than 2% of the world's annual energy supply by Haber–Bosch process and the strongest triple bond (N≡N) in nature, directly coupling N2 with small molecules is particularly important and challenging, let alone in a catalytic fashion. Here we first demonstrate that a NNN‐type pincer phosphorus complex could act as a catalyst to couple dinitrogen with a series of small molecules including carbon dioxide, formaldehyde, N‐ethylidenemethylamine, and acetonitrile in the presence of diborane(4) under a mild condition by theoretical calculations. N2 fixation proceeds via a stepwise mechanism involving initial N2 activation by diborane(4), followed by intramolecular isomerization to a key intermediate (zwitterion). Such a zwitterion can be used to couple a series of small molecules with activation barriers of 23.5–25.2 kcal mol−1. All these findings could be particularly useful for main group chemistry aimed at N2 activation. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2, a common combustion pollutant) releasing continuously into the atmosphere is primarily responsible for the rising atmospheric temperature. Therefore, CO2 sequestration has been an indispensable area of research for the past several decades. On the other hand, the concept of aromaticity is often employed in designing chemical reactions and metal‐free frustrated Lewis pairs (FLPs) have proved ideal reagents to achieve CO2 reduction. However, considering FLP and aromaticity together is less developed in CO2 capture. Here we report theoretical investigations on the aromaticity‐promoted CO2 activation, involving heterocyclopentadiene‐bridged P/N‐FLPs. The calculations reveal that furan‐ and pyrrole‐bridged P/N‐FLPs can make CO2 capture both thermodynamically and kinetically favorable (with activation energies of 5.4–7.7 kcal mol−1) due to the aromatic stabilization of the transition states and products. Our findings could open an avenue to the design of novel FLPs for CO2 capture. [ABSTRACT FROM AUTHOR]

Benzene, the prototype of aromatics, has six equivalent C−C bonds (1.397 Å), which are intermediate between a C−C double bond and a C−C single bond. For over 80 years, chemists have spent much effort on freezing a localized structure to obtain a distorted bond‐length alternating benzene ring in the ground state, leading to various localized trisannelated benzene rings. However, most of the central benzene rings are still aromatic or nonaromatic. Here we report an antiaromatic benzene ring caused by hyperconjugation. Specifically, symmetric annulation of 5,5‐difluorocyclopentadiene results in an antiaromatic benzene ring, which is supported by various aromaticity indices, including nucleus‐independent chemical shift, anisotropy of the induced current density, π‐separated electron‐localization function and heat of hydrogenation. Our findings highlight a strong power of hyperconjugation, a "weak" interaction in organic chemistry, paving the way for designing and realizing more novel (anti)aromatics. [ABSTRACT FROM AUTHOR]

Unusual 1,2‐migration reactions of N‐heterocyclic carbene (NHC) on transition metals were investigated using density functional theory calculations. Our results reveal that the electronic properties, ring strain of the four‐membered ring, and aromaticity of NHC play crucial roles in the thermodynamics of such a 1,2‐migration. Further studies show that changing the methylene on the metal center in the reactant with a more electronegative group (NH or O) will lead to the formation of products with nitrogen coordinating to the metal center, whereas other groups (BH, CF2, and SiH2) will make such a 1,2‐migration reverse. In addition, the reversed rearrangement of 1,2‐boron, silyl migration could be thermodynamically and kinetically favorable. [ABSTRACT FROM AUTHOR]

The [1,5]‐migration reaction has attracted considerable attention from experimentalists and theoreticians for decades. Although it has been extensively investigated in various systems, studies on pyrrolium derivatives are underdeveloped. Herein, a theoretical study on the reaction mechanism of [1,5]‐migration in both pyrrolium and pyrrole derivatives is presented. The results reveal lower activation barriers in [1,5]‐migration of electropositive groups (AuPMe3 and SnH3) in pyrrolium derivatives, although the bond dissociation energies of the Au−N bond (98.8 kcal mol−1) and Sn−N bond (81.7 kcal mol−1) are larger than that of the N−F bond (57.6 kcal mol−1). The unexpectedly lower activation barriers (4.5 and 4.9 kcal mol−1 for AuPMe3 and SnH3, respectively) for [1,5]‐migration of electropositive groups, in comparison with the [1,5]‐fluorine shift, can be attributed to aromaticity stabilizing the transition states, as revealed by significantly negative nucleus‐independent chemical shift (NICS) values. Further studies indicate that charge distribution and frontier molecular orbitals also play some roles in [1,5]‐migration of pyrrolium derivatives. [ABSTRACT FROM AUTHOR]

Fluorine is the most electronegative element in the periodic table. Thus, activation of the carbon–fluorine (C−F) bond, the strongest single bond to carbon, has attracted considerable interest from both experimentalists and theoreticians. In comparison with numerous approaches to activate C−F bonds, the aromaticity‐promoted method is less developed. Herein, we demonstrate that the C−F bond activation could be achieved by a facile tautomerization, benefitting from aromaticity, which can stabilize both the transition states and products. Our findings highlight an important application of aromaticity in the C−F bond activation, providing experimentalists with an alternative approach to activate C−F bonds. [ABSTRACT FROM AUTHOR]

Aromaticity is one of the most fundamental and fascinating chemical topics, attracting both experimental and theoretical chemists owing to its many manifestations. Both σ‐ and π‐aromaticity can be classified depending on the character of the cyclic electron delocalization. In general, σ‐aromaticity stabilizes fully saturated rings with σ‐electron delocalization whereas the traditional π‐aromaticity describes the π‐conjugation in fully unsaturated rings. Here, we demonstrate a strong correlation between nucleus‐independent chemical shift (NICS) values and extra cyclic resonance energies (ECREs), which are used to evaluate the σ‐aromaticity in an unsaturated three‐membered ring (3MR) of cyclopropene, which were computed by molecular orbital (MO) theory and valence bond (VB) theory, respectively. Further study shows that the fully unsaturated ring in methylenecyclopropene and its metallic analogy is σ‐aromatic. Our findings revolutionize the fundamental knowledge of the concept of σ‐aromaticity, thus opening an avenue to design σ‐aromaticity in other fully unsaturated systems, which are traditionally reserved as the domain of π‐aromaticity. σ‐Aromaticity dominating in a fully unsaturated ring is reported, revolutionizing the fundamental scope of the concept of σ‐aromaticity, thus opening an avenue to design σ‐aromaticity in other fully unsaturated systems, which were traditionally reserved as the domain of π‐aromaticity. [ABSTRACT FROM AUTHOR]

Abstract: Hyperconjugation, a weak interaction in organic chemistry, can have a strong effect on aromaticity, leading to the concept of hyperconjugative aromaticity, which was first proposed by Mulliken in 1939. However, most studies are limited to main group chemistry. Here we report the most aromatic and antiaromatic pyrrolium ring by maximizing the hyperconjugation caused by transition metal fragments and the push–pull effect. Our calculations reveal that the origin of the outperformance of transition metal substituents over main group ones on hyperconjugative aromaticity could be attributed to their higher highest occupied molecular orbitals (HOMOs). Among the group 11 transition metals, a silver substituent results in the best performance. All these findings highlight the magic of the transition metal (silver) and could be particularly helpful for the design of other aromatic and antiaromatic counterparts based on a nonaromatic parent species. [ABSTRACT FROM AUTHOR]

The enhancement of microbial activity and electrocatalysis through the design of new anode materials is essential to develop microbial fuel cells (MFCs) with longer lifetimes and higher output. In this research, a novel anode material, graphene/Fe3O4 (G/Fe3O4) composite, has been designed for Shewanella-inoculated MFCs. Because the Shewanella species could bind to Fe3O4 with high affinity and their growth could be supported by Fe3O4, the bacterial cells attached quickly onto the anode surface and their long-term activity improved. As a result, MFCs with reduced startup time and improved stability were obtained. Additionally, the introduction of graphene not only provided a large surface area for bacterial attachment, but also offered high electrical conductivity to facilitate extracellular electron transfer (EET). The results showed that the current and power densities of a G/Fe3O4 anode were much higher than those of each individual component as an anode. [ABSTRACT FROM AUTHOR]

A general rule towards thermodynamic stabilities of mono BN ‐ doped lower polyenes is proposed based on high ‐ level calculations, which could help experimentalists to synthesize isomers with particular thermodynamic stability. Specifically, isomers with terminal nitrogen and direct B−N bond (illustrated on the bottom) are found to be the most stable ones whereas highly destabilized isomers (illustrated on the top) are those with one terminal methylene group and one terminal heteroatom. More information can be found in the Full Paper by Jun Zhu et al. on page   605 in Issue 5, 2017 (DOI: 10.1002/asia.201601753). [ABSTRACT FROM AUTHOR]

The article offers information on the 10-year history of the Asian Core Program on Cutting-Edge Organic Chemistry in Asia (ACP-CEOCA). Topics discussed include the brief history of the program, its aims and objectives from October 2005 to March 2015, and its influence to the chemistry-related community in Thailand. Information on the ACP in Malaysia, Mainland China, and Singapore is also given.

A convergent protecting group-free total synthesis route of camptothecin and 10-hydroxycamptothecin has been developed in this work. Cascade oxidation of 3-(hydroxymethyl)furan-2(5 H)-one and in situ intermolecular oxa Diels-Alder reaction with vinyl ether was developed and applied to construct the E-ring, and TMSCl-promoted cascade closure of the D-ring delivered the whole skeleton of the alkaloids in the total synthesis. The new short syntheses were advantageous with regard to step economy, low cost, easily available starting materials and reagents, and convenient operations. [ABSTRACT FROM AUTHOR]

Enantioselective total syntheses of lycopodium alkaloids lycoposerramine-V and 5- epi-lycoposerramine-V have been accomplished. Features of the newly established total synthesis include: 1) introduction of the first chiral center with a scalable desymmetrization reaction of an meso-anhydride; 2) chemoselective functionalization of a bis-Weinreb-amide with Grignard addition; and 3) construction of the multifunctionalized cyclohexanone with a stereoselective intramolecular Michael addition. [ABSTRACT FROM AUTHOR]

Theoretical calculations reveal that five ‐ membered cyclic species with “hyperconjugative” aromaticity (and antiaromaticity) in the S0 state will become antiaromatic (and aromatic) in the T1 state (aromaticity is denoted by a delocalized large semicircle in the picture), in line with Baird's rule. In addition, NICS criterion and charge effects on triplet state aromaticity are also discussed. More information can be found in the Full Paper by Jun Zhu et   al. on page   234 in Issue 2, 2016 (DOI:10.1002/asia.201500897). [ABSTRACT FROM AUTHOR]

Spectator or actor? Density functional theory calculations were performed to examine the role of the base in the nickel ‐ catalyzed cross ‐ coupling of aryl phosphates with arylboronic acids. Potassium phosphate was found to not act as a spectator base but was involved in the transmetalation step, as shown by a lower barrier than that of a base ‐ free process, owing to the activation of the carbonboron bond by the base. Further experimental observations support the theoretical findings. [ABSTRACT FROM AUTHOR]

Anchoring groups are extremely important in controlling the performance of dye-sensitized solar cells (DSCs). The design and characterization of sensitizers with new anchoring groups, in particular non-carboxylic acid groups, has become a recent focus of DSC research. Herein, new donorπacceptor zincporphyrin dyes with a pyridine ring as an anchoring group have been designed and synthesized for applications in DSCs. Photophysical and electrochemical investigations demonstrated that the pyridine ring worked effectively as an anchoring group for the porphyrin sensitizers. DSCs that were based on these new porphyrins showed an overall power-conversion efficiency of about 4.0 % under full sunlight (AM 1.5G, 100 mW cm−2). [ABSTRACT FROM AUTHOR]

σ‐Aromaticity dominating in a fully unsaturated ring (the three‐membered ring of methylenecyclopropene and its metallic analog) is reported, revolutionizing the fundamental scope of the concept of σ‐aromaticity, thus opening an avenue to design σ‐aromaticity in other fully unsaturated systems (illustrated by the upper right of a Tai Chi circle), which are traditionally reserved for the domain of π‐aromaticity. More information can be found in the Full Paper by Jun Zhu et al. on page 3691 in Issue 23, 2018 (DOI: 10.1002/asia.201801279). [ABSTRACT FROM AUTHOR]