Molecular nitrogen (N2), an abundant component of the atmosphere, is appealing for industrial value‐added products. However, its intrinsic inertness limits its activation to mainly metallic species. Environmental concerns and harsh reaction conditions have resulted in a demand for alternate nonmetallic and nontoxic routes to activate and functionalize N2 at ambient conditions. Comprehensive density functional theory (DFT) calculations are performed on N2 activation by boron species, specifically for the experimentally more accessible tricoordinated boron compounds. Subsequently designed frustrated Lewis pairs (FLPs) combining screened N‐heterocyclic carbene with boron moieties can make N2 activation both kinetically and thermodynamically favorable, displaying high potential for metal‐free N2 activation. The significant thermodynamic stability of the products stabilized by aromaticity and low activation barriers could be a breakthrough for the development of FLP chemistry on metal‐free N2 activation.

Carbon dioxide (CO 2 ,acommon combustion pollutant) releasing continuously into the atmosphere is primarily responsible for the rising atmospheric temperature. Therefore, CO 2 sequestration has been an indispensable area of research for the past severald ecades. On the other hand, the concept of aromaticity is often employed in designing chemical reactions and metal-free frustratedL ewis pairs (FLPs) have proved ideal reagents to achieveC O 2 reduction. However,c onsidering FLP and aromaticity together is less developed in CO 2 capture. Here we report theoretical investigationsonthe aromaticity-promoted CO 2 activation,involving heterocyclopentadiene-bridged P/N-FLPs. The calculations revealt hat furan-and pyrrole-bridged P/N-FLPs can make CO 2 capture both thermodynamically and kinetically favorable (with activation energies of 5.4-7.7 kcal mol À1 )d ue to the aromatic stabilization of the transition states and products.O ur findings could open an avenue to the design of novel FLPs for CO 2 capture.

Activation of the strongest triplet bond in molecular nitrogen (N 2 ) under mild conditions is particularly challenging. Recently, its fixation and reduction were achieved by highly reactive dicoordinated borylene species at ambient conditions, ripping the limits of harsh reaction conditions by metallic species. Less reactive species with a facile preparation could be desirable for nextgeneration N 2 activation. Now density functional theory calculations reveal that tricoordinated boranes could be a potential candidate of N 2 activation/ functionalization. As composites of an intramolecular frustrated Lewis pair (FLP), optimal and realistic boranes are screened out to activate N 2 in a significantly favorable manner (both thermodynamically and kinetically). The significant thermodynamic stabilities of the FLP−N 2 adducts as well as the low activation barriers could be particularly interesting for the development of boranebased FLP chemistry applied in N 2 activation.

Activation of atmospherically abundant dinitrogen (N2) by metal-free species under mild reaction conditions has been one of the most challenging areas in chemistry for decades. Very recent but limited progress in N2 activation by boron species, including two-coordinated borylene and methyleneborane and three-coordinated borole and borane, has been made toward metal-free N2 activation. Here, we systematically probe an experimentally viable frustrated Lewis pair (FLP) containing two moieties (methyleneborane and carbene) for N2 activation via density functional theory (DFT) calculations, which has proven to be an efficient approach for N2 activation in a thermodynamically and kinetically favorable manner. Aromaticity is found to play a crucial role in stabilization of the product. This study could be a valuable alternative for the development of metal-free N2 activation chemistry, highlighting great potential of FLP for N2 activation and functionalization.

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.

Quantum chemical calculations with the M06-2X, B3LYP, and B3LYP-D2 density functional theory methods were performed in order to examine the formation of Brook-type silabenzenes 4a−n through [1,3]-trimethylsilyl (TMS) and [1,3]-triisopropylsilyl (TIPS) shifts from a tetrahedral silicon atom to an adjacent carbonyl oxygen of cyclic conjugated acylsilane precursors. All Brook-type silabenzenes, having a 2-trialkylsiloxy substituent, are at lower relative energies than their precursors. The free energy of activation at the M06-2X/6-311+G(d,p) level for the thermal [1,3]-silyl shifts leading to the smallest Brook-type silabenzene (4a) is 30.2 kcal/mol, and it is 27.5 kcal/mol for a silabenzene (4l) with TIPS, OTIPS, and tert-butyl substituents. The geometries and nucleus-independent chemical shifts (NICS) of the Brooktype silabenzenes indicate aromatic character. The [4 + 2], [2 + 2], and [4 + 4] cycloaddition dimers were also studied. At the M06-2X/6-311+G(d)//M06-2X/6-31G(d) and B3LYP-D2/6-31G(d) levels, i.e., two DFT methods which accurately describe nonbonded dispersive interactions, most Brook-type silabenzene dimers studied herein are lower in energy than two silabenzenes. The activation energies for dimerization of 4l to either of two [4 + 2] cycloadducts (25.7 and 29.6 kcal/mol with M06-2X/6-31G(d)) suggest that this silabenzene potentially can exist as a monomer at ambient temperature. However, the transition state structures for the dimerization of 4l reveal where further bulk should be added, leading to silabenzene 4n, a species for which dimerization is endothermic or only slightly exothermic.

Metallaaromatics have attracted considerable attention in recent years because they can display properties of both organic and organometallic species. However, it remains unclear whether Clar's rule could be applied to organometallic chemistry despite its proposal in 1950s. Here, we investigate the relative stabilities of 49 organic and organometallic species by density functional theory (DFT) calculations. The results indicate that the nonmetal-bridged isomers are more stable than the metalbridgehead ones, and the kinked isomers are more stable than its linear isomers, extending Clar's rule to organometallic chemistry and aryne chemistry. Our findings provide useful information for experimental chemists to realize more metallaaromatics, as some predicted osmatricycles are thermodynamically more stable than the experimentally isolated ones.

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.