Grignard reagent formation via C-F bond activation: a centenary perspective

Examples of Grignard reagents obtained by C-F bond activation with magnesium kept appearing in the literature over the last century. Due to the high bond dissociation energy of the C-F...

Photodissociation of dicarbon: How nature breaks an unusual multiple bond

The dicarbon molecule (C2) is found in flames, comets, stars, and the diffuse interstellar medium. In comets, it is responsible for the green color of the coma, but it is not found in the tail. It has long been held to photodissociate in sunlight with a lifetime precluding observation in the tail, but the mechanism was not known. Here we directly observe photodissociation of C2. From the speed of the recoiling carbon atoms, a bond dissociation energy of 602.804(29) kJ·mol−1 is determined, with an uncertainty comparable to its more experimentally accessible N2 and O2 counterparts. The value is within 0.03 kJ·mol−1 of high-level quantum theory. This work shows that, to break the quadruple bond of C2 using sunlight, the molecule must absorb two photons and undergo two “forbidden” transitions.

Theoretical Insight into 20-Electron Transition-Metal Complexes (C5H5)2TM(E1E2)2 (TM = Cr, Mo, W; E1E2 = CO, N2, BF): Stabilities, Electronic Structures, and Bonding Nature

A systematic first-principles study is performed to investigate the 20-electron transition metal complexes (CH)TM(EE) (TM = Cr, Mo, W; EE = CO, N, BF). The bond dissociation energy (De) based on (CH)TM(EE) → (CH)TM(EE) + EE indicates much lower thermodynamic stability of (CH)TM(N) because of poor binding ability of N ligands. For the thermodynamic stable (CH)TM(EE) complexes (TM = Cr, Mo, W; EE = CO, BF), their 20-electron nature is derived from their occupied nonbonding molecular orbital mainly donated by ligands. Furthermore, charge transfer from TMs to the CH ligands is revealed by the atoms in molecules (AIM) theory, leading to the positive charges of the TM atoms. On the other hand, the nature of the TM-E bond has been thoroughly analyzed by the energy decomposition analysis (EDA) method. The absolute value of interaction energies (|ΔE|) between (CH)TM(EE) and EE has the same trend as the corresponding bond dissociation energy and Wiberg bond orders of TM-E bonds, following the order W > Mo > Cr with same ligands and BF > CO with same TM. Additionally, the largest contribution to the ΔE values is the repulsive term ΔE. Similar contributions from covalent and electrostatic terms to the TM-E bonds were found, which can be described as the classic dative bond with nearly same σ and π contributions. The stronger σ donations and π backdonations in (CH)TM(BF) than in (CH)TM(CO) indicate much more stability of (CH)TM(BF).

Benchmark calculations for bond dissociation energies and enthalpy of formation of chlorinated and brominated polycyclic aromatic hydrocarbons

Benchmark calculations using state-of-the-art DFT functionals and composite methods for bond dissociation energy and enthalpy of formation of halogenated polycyclic aromatic hydrocarbons are performed.

Insight into the chemoselective aromatic vs. side-chain hydroxylation of alkylaromatics with H2O2 catalyzed by a non-heme imine-based iron complex

Side-chain/ring oxygenated product ratio increases upon decreasing the benzylic bond dissociation energy in the oxidation of alkylaromatics with H2O2 catalyzed by an imine-based iron complex.