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.

Discovery of species with adaptive aromaticity, being aromatic in both the lowest‐lying singlet and triplet states (S0 and T1), is a significant challenge because cyclic conjugated complexes are commonly aromatic in one state only according to Hückel's and Baird's rules. On other hand, the carbone ligands containing two lone pair electrons at the carbon(0) atom have attracted considerable attention from both theoretical and experimental chemists recently. Here, we carry out density functional theory (DFT) calculations on osmapentalene and osmapyridinium complexes with carbone ligands to examine their aromaticity in both the S0 and T1 states. It is found that these complexes can possess adaptive aromaticity, supported by various aromaticity indices including the harmonic oscillator model of aromaticity (HOMA), nucleus‐independent chemical shift (NICS), anisotropy of the induced current density (ACID), electron density of delocalized bonds (EDDB), and the change of heat of hydrogenation (∆∆H). Our findings expand the scope of the concept of adaptive aromaticity, inviting experimental chemists' verification to enrich aromatic organometallic chemistry.

The conversion of dinitrogen to more useful and reactive molecules has been the focus of intense research by chemists. In contrast to reductive N2 fixation, direct oxidation of N2 by O2 to nitric oxide under mild conditions via a thermochemical process is extremely challenging. Herein, we report the first example of N2 and O2 activation and coupling under thermochemical conditions through the remarkable ability of Y2BO+ to react with one N2 and two O2 molecules. Detailed mechanistic studies using mass spectrometry and quantum chemical calculations revealed that the N2 activation by Y2BO+ is facilitated by the double aromatic character of the Y2BON2 + intermediate. Subsequent oxidation with O2 releases NO in a dearomatization process driven by the formation of stronger Y–O bonds over the Y–N bonds. Our findings represent the first example of N2 and O2 activation and coupling under thermochemical conditions at room temperature, providing a novel strategy for small-molecule activation.