Although the carbene-catalyzed N2 fixation process had been investigated by scientists for decades prior to borylene species, the interest in the carbene-mediated N2 activation process has drawn less attention than that of borylene species in the past few years, especially unique σ0π2 carbenes. Herein, we demonstrate the important role of unique σ0π2 carbenes in the 1,1-hydroboration and bis-carbene functionalization of N2 using density functional theory calculations.

Activation of dinitrogen (N2) under mild conditions has been a particularly challenging project for decades, owing to the highly strong N≡N triple bond. In recent years, the main group species have emerged as a prominent strategy in the field of dinitrogen activation, but the reported examples remain particularly rare compared with transition metal complexes. Herein, we performed a comprehensive density functional theory (DFT) calculation of N2 activation by boron radical cations.

Ring contraction of metallacyclobutadiene to metallacyclopropene is rare because of the increasing strain from a four-membered ring to a three-membered one. Here we demonstrate a new series of reactions of metallabenzocyclobutadiene to metallabenzocyclopropene via density functional theory calculations. The results suggest that these reactions are thermodynamically favorable ranging from −17.4 to −29.4 kcal mol–1, and a low reaction barrier (10.3 kcal mol–1) is achieved when the metal center is Ru and the ligands are one cyanide and one chloride.

Aromaticity is a fundamental concept in organic chemistry. Hyperconjugative aromaticity, also known as hyperconjugation-induced aromaticity, has evolved from its origin from main group substituents to transition metal analogues, establishing itself as an important category of aromaticity. Additionally, aromatic compounds comprising two sp3-carbon atoms have recently been reported both experimentally and computationally. However, what is the maximum number of sp3-hybridized atoms needed to maintain hyperconjugative aromaticity?

Although main group species have emerged in the field of dinitrogen activation in recent years, the reported examples are particularly rare in comparison with transition metal complexes due to their significant challenges. Herein, we demonstrate a [4 + 2] cycloaddition reaction of N2 (with an activation energy as low as 12.5 kcal mol–1) initiated by an inorganic benzene via density functional theory calculations. Such N2 activation is supported by the elongated nitrogen–nitrogen bond distance (dNN), decreased vibration frequency (νNN), and weakened Wiberg bond index (WBINN).

Although the main group species in the s and p blocks have begun to gain prominence in the field of dinitrogen (N2) activation in recent years, reports of carbene-mediated N2 activation remain particularly rare, especially for carbenes with a σ0π2 electronic configuration. Herein, we demonstrate examples of N2 activation initiated by a carbene with a σ0π2 electronic configuration and consequent N2 hydroboration reaction (with a reaction barrier as low as 19.9 kcal/mol) via density functional theory calculations.

Complexes with aromaticity in both the lowest singlet state (S0) and the lowest triplet state (T1) (denoted as adaptive aromaticity) are rare because according to Hückel’s and Baird’s rules, a species could be aromatic in either the S0 or T1 state in most cases. Thus, it is particularly challenging to design species with adaptive aromaticity. Previous reports on adaptive aromaticity were mainly focused on 16e metallapentalenes.

The 18-electron rule states that metal complexes with 18 valence electron metal centers are thermodynamically stable because nine valence orbitals of transition metals including one s orbital, three p orbitals, and five d orbitals can collectively accommodate 18 electrons, achieving the same electron configuration as the noble gas in the period. Thus, 20-electron compounds are extremely rare due to a violation of such a rule.

Due to the high bond dissociation energy (945 kJ mol–1) and the large highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gap (10.8 eV), dinitrogen activation under mild conditions is extremely challenging. On the other hand, the conventional Haber–Bosch ammonia synthesis under harsh conditions consumes more than 1% of the world’s annual energy supply. Thus, it is important and urgent to develop an alternative approach for dinitrogen activation under mild conditions.

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.