Inorg. Chem.

Design of Borole- and Silylene-Based Frustrated Lewis Pairs for Dinitrogen Activation Promoted by Aromaticity: A Combined DFT and Machine Learning Study

In recent years, while main-group elements from the s- and p-block have emerged in the field of N2 activation, silylenes─despite their remarkable successes in the activation of diverse small molecules─remain unreported for N2 activation. Herein, we design “silylene-borole” frustrated Lewis pairs (FLPs) by combining silylene moieties with boron components and conduct comprehensive density functional theory (DFT) calculations to thoroughly investigate their potential for N2 activation.

Predicting Dinitrogen Activation and Coupling with Carbon Dioxide and Other Small Molecules by Methyleneborane: A Combined DFT and Machine Learning Study

The capture of carbon dioxide is extremely important due to the increasingly severe greenhouse effect, and the conversion of dinitrogen into high-value N–C compounds is of great significance. Here, we predict through density functional theory calculations that the coupling of dinitrogen with carbon dioxide by methyleneborane becomes favorable both thermodynamically and kinetically. Machine learning analysis suggests that increasing the HOMO–LUMO gap or the charge on the boron atom or decreasing the charge of the nitrogen atom will reduce the reaction energies.

Predicting σ0π2 Carbene-Mediated Hydroboration and Bis-carbene Functionalization of Dinitrogen

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.

Predicting Dinitrogen Activation by Boron Radical Cations

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.

Probing σ-Aromaticity-Driven Ring Contraction of Metallabenzocyclobutadiene to Metallabenzocyclopropene

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.

Probing the Limit of the Number of Saturated Atoms for Achieving Hyperconjugative Aromaticity

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?

Predicting Small Molecule Activations Including Dinitrogen Based on an Inorganic Benzene B4N2 Framework

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).

Predicting Activation of Small Molecules Including Dinitrogen via a Carbene with a σ0π2 Electronic Configuration

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.

Adaptive Aromaticity in 18e Metallapentalenes

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.

Stabilizing a 20-Electron Metallaazulyne by Aromaticity

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.

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