Understanding the Mechanism and Selectivity of 1,1-Diborylalkanes from Alkenes Catalyzed by a Zirconium Complex

The synthesis of 1,1-diborylalkanes from readily available alkenes is an appealing method. The density functional theory (DFT) method was employed to investigate the reaction mechanism of 1,1-diborylalkanes, which was synthesized from alkenes and a borane, and the reaction was catalyzed by a zirconium complex Cp₂ZrCl₂. The entire reaction is divided into two cycles: dehydrogenative boration to form vinyl boronate esters (VBEs) and hydroboration of VBEs. This article focuses on the hydroboration cycle and elaborates on the role of the reducing reagents in the equilibrium of self-contradictory reactivity (dehydrogenative boration and hydroboration). The H₂ and HBpin pathways were investigated as the reducing reagents in the hydroboration process. The calculated results showed that it is more advantageous to use H₂ as a reducing agent (path A). Furthermore, the σ-bond metathesis is the rate-determining step (RDS) with an energetic span of 21.4 kcal/mol. This is consistent with the self-contradictory reactivity balance proposed in the experiment. The reaction modes of the hydroboration process were also discussed. These analyses revealed the origin of selectivity in this boration reaction, in which the σ-bond metathesis of HBpin needs to overcome the strong interaction between HBpin and the Zr metal. Meanwhile, the origin of the selectivity of different positions of H₂ is the interaction between the σ(H¹-H²) → σ*(Zr¹-C¹) overlap and these findings have implications for catalyst design and application.

Density Functional Theory Study on the H2-Acceptorless Dehydrogenative Boration of Alkenes Catalyzed by a Zirconium Complex

For the synthesis of vinyl boronate esters, the direct catalytic H₂-acceptorless dehydrogenative boration of alkenes is one of the promising strategies. In this paper, the density functional theory method was employed to investigate the reaction mechanism of dehydrogenative boration and transfer boration of alkenes catalyzed by a zirconium complex (Cp₂ZrH₂). There are two possible pathways for this reaction: the alkene insertion followed by the dehydrogenative boration (path A) and the alkene insertion after the dehydrogenative boration (path B). The calculated results showed that path A is more favorable than path B, and that the rate-determining step is the C-B coupling step with an energy barrier of 18.7 kcal/mol. The reaction modes of the C-B coupling assisted dehydrogenative boration and the alkene insertion were also discussed. These analyses reveal a novel hydrogen release behavior in dehydrogenative boration and the alkene insertion modes and sequences were proposed to be of importance in the chemoselectivity of this reaction. In addition, the X ligand effect (X = H, Cl) on the catalytic activity of the zirconium complex was explored, indicating that the H ligand could enhance the catalytic activity of the complex for styrene dehydrogenative boration.

Palladium-Catalyzed Regio- and Chemoselective Double-Alkoxycarbonylation of 1,3-Diynes: A Computational Study

The palladium-catalyzed double-alkoxycarbonylation of 1,3-diynes provides an efficient approach for the selective synthesis of 1,2,3,4-tetrasubstituted conjugated dienes. In this report, density functional theory calculations have been performed to elucidate the...

Mechanism and origins of stereo- and enantioselectivities of palladium-catalyzed hydroamination of racemic internal allenes via dynamic kinetic resolution: a computational study

DFT calculations were performed to investigate the Pd-catalyzed hydroamination of racemic internal allenes with pyrazoles.

Highly Chemo-, Regio- and E/Z-Selective Intermolecular Heck-Type Dearomative [2 + 2 + 1] Spiroannulation of Alkyl Bromoarenes with Internal Alkynes

Described herein is a palladium-catalyzed dearomative annulation of alkyl bromoarenes with internal alkynes. Challenges in this spiroannulation include the chemoselectivity among [2 + 2 + 1], [2 + 2 + 2], and [3 + 2] annulations and the E/ Z-selectivity associated with the generated exocyclic double bond. In the presence of Pd(OAc)₂ and a phosphine ligand, a variety of highly functionalized spirocyclopentadienes with an exocyclic carbon-carbon double bond are provided in good to excellent yields with high chemo-, regio-, and E/ Z-selectivity via a Heck-type pathway.