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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]

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]

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]

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]

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]