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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]

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]

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]