C(sp3)–F Bond Activation and Hydrodefluorination of the CF3 Group Catalyzed by a Nickel(II) Hydride Complex: Theoretical Insight into the Mechanism with a Spin-State Change and Two Ion-Pair Intermediates

Nickel-catalyzed regiodivergent hydrosilylation of α-(fluoroalkyl)styrenes without defluorination

The fluoroalkyl-containing organic molecules are widely used in drug discovery and material science. Herein, we report ligand regulated nickel(0)-catalyzed regiodivergent hydrosilylation of α-(fluoroalkyl)styrenes without defluorination, providing an atom- and step-economical synthesis route of two types of fluoroalkyl substituted silanes with exclusive regioselectivity. The anti-Markovnikov addition products (β-fluoroalkyl substituted silanes) are formed with monodentate phosphine ligand. Noteworthy, the bidentate phosphine ligand promote the generation of the more challenging Markovnikov products (α-fluoroalkyl substituted silanes) with tetrasubstituted saturated carbon centers. This protocol features with easy available starting materials and commercially available nickel catalysis, a wide range of substrates and excellent regioselectivity. The structure divergent products undergo a variety of transformations. Comprehensive mechanistic studies including the inverse kinetic isotope effects demonstrate the regioselectivity controlled by ligand structure through α-CF3 nickel intermediate. DFT calculations reveal a distinctive mechanism involving an open-shell singlet state, which is crucial for generating intricate tetra-substituted Markovnikov products.

DFT calculations in solution systems: solvation energy, dispersion energy and entropy

DFT calculations of reaction mechanisms in solution have always been a hot topic, especially for transition-metal-catalyzed reactions. The calculation of solvation energy is performed using either the polarizable continuum model (PCM) or the universal solvation model SMD. The PCM calculation is very sensitive to the choice of atomic radii to form a cavity, where the self-consistent isodensity PCM (SCI-PCM) has been recognized as the best choice and our IDSCRF radii can provide a similar cavity. Moving from a gas-phase case to a solution case, dispersion energy and entropy should be carefully treated. The solvent-solute dispersion is also important in solution systems, and it should be calculated together with the solute dispersion. Only half of the solvent-solute dispersion energy from the PCM calculation belongs to the solute molecules to maintain a thermal equilibrium between a solute molecule and its cavity, similar to the treatment of electrostatic energy. Relative solute dispersion energy should also be shared equally with the newly formed cavity. The entropy change from a gas phase to a liquid phase is quite large, but the modern quantum chemistry programs can only calculate the gas-phase translational entropy based on the idea-gas equation. In this review, we will provide an operable method to calculate the solution translational entropy, which has been coded in our THERMO program.

Theoretical Insight into the Multiple Roles of LiHMDS in Pd-Catalyzed Borylation of Fluorobenzene

Pd-catalyzed borylation of fluorobenzene was theoretically studied. DFT calculations revealed that the reaction occurs through an unprecedented 3 + 6-membered ring transition state, in which one LiHMDS (HMDS = hexamethyldisilazane) acts as a ligand and another LiHMDS is essential to provide Li···N and Li···F interactions, overcoming the large destabilization of the strong phenyl-F bond distortion. The characteristic feature of LiHMDS was elucidated by comparing it with HMDS and NaHMDS analogues.

Selective Nickel-Catalyzed Hydrodefluorination of Amides Using Sodium Borohydride

Hydrodefluorination selective to the ortho position to amides is accomplished under mild conditions using sodium borohydride and a nickel catalyst. The facile formation of a nickelacycle intermediate with a specific geometry ensures selectivity without the need for electronic directing groups, and fluorine atoms in other positions remain intact. This method avoids the use of stoichiometric silanes which are typical for most other defluorination reactions, resulting in virtually no organic waste byproducts.

A Carbene Strategy for Progressive (Deutero)Hydrodefluorination of Fluoroalkyl Ketones

Hydrodefluorination is one of the most promising chemical strategies to degrade perfluorochemicals into partially fluorinated compounds. However, controlled progressive hydrodefluorination remains a significant challenge, owing to the decrease in the strength of C-F bonds along with the defluorination. Here we describe a carbene strategy for the sequential (deutero)hydrodefluorination of perfluoroalkyl ketones under rhodium catalysis, allowing for the controllable preparation of difluoroalkyl- and monofluoroalkyl ketones from aryl- and even alkyl-substituted perfluoro-alkyl ketones in high yield with excellent functional group tolerance. The reaction mechanism and the origin of the intriguing chemoselectivity of the reaction were rationalized by density functional theory (DFT) calculations.