Regioselective Tandem C–H Alkylation/Coupling Reaction of ortho-Iodophenylethylenes via C,C-Pallada(II)cycles

Palladium-Catalyzed Sequential Cross-Coupling/Annulation of ortho-Vinyl Bromobenzene with Aryl Bromide: Bimetallic Pathway versus Pd(II)-Pd(IV) Pathway: A DFT Investigation

The palladium-catalyzed sequential cross-coupling/annulation of ortho-vinyl bromobenzenes with aryl bromides generating phenanthrenes was characterized by density functional theory (DFT). The Pd(II)-Pd(IV) pathway (Path V) is shown to be less probable than the bimetallic pathway (Path I), the latter proceeding via the following six steps: oxidative addition, vinyl-C(sp2)-H activation, Pd(II)-Pd(II) transmetalation, C-C coupling, aryl-C(sp2)-H activation, and reductive elimination. The aryl-C(sp2)-H activation process acts as the rate-determining step (RDS) of the entire chemical transformation, with an activation free energy barrier of ca. 27.4-28.8 kcal·mol-1, in good agreement with the corresponding experimental data (phenanthrenes' yields of ca. 65-90% at 130 °C after 5 h of reaction). The K2CO3 additive effectively reduces the activation free energy barrier of the RDS through direct participation in the reaction while preferentially modulating the charge distributions and increasing the stability of corresponding intermediates and complexes along the reaction path. Furthermore, bonding and electronic structure analyses of the key structures indicate that the chemo- and regioselectivities of the reaction are strongly influenced by both electronic effects and steric hindrance.

Palladium-catalyzed disilylation of ortho-halophenylethylenes enabled by 2-pyridone ligand

A palladium-catalyzed disilylation reaction applicable for a variety of non-, α-, or β-substituted and α,β-disubstituted ortho-halophenylethylenes has been developed. This reaction proceeds with high yields and very low catalyst loadings. The two C-Si bonds of the disilylated products could be well-differentiated chemoselectively in the reaction with various electrophiles.

Regioselective C-H Active Carbonylation via 1,4-Palladium Migration

We report a highly regioselective three-component coupling reaction of styrene, CO gas, and an amine compound to synthesize multisubstituted α,β-unsaturated amides, which involves a palladium-catalyzed sequential 1,4-palladium migration, C(sp²)-H activation, carbonylation, and amination. Salient features of this strategy include the use of 1 atm of CO, excellent stereochemistry, and good functional group tolerance. Further, a series of control experiments and density functional theory calculations were performed to afford some insights for the transfer mechanism.

Diverse Synthesis of Alkenylsilanes via Pd-Catalyzed Alkenyl C-H Silylation

Here, we disclose a general approach for the diverse synthesis of alkenylsilanes in a highly efficient, stereoselective, and atom-economic manner by leveraging the palladium-catalyzed disilylation reaction of 2-bromostyrene derivatives with hexamethyldisilane, which is suitable for the preparation of a series of disubstituted, trisubstituted, and tetrasubstituted alkenylsilanes. Furthermore, the resulting tetrasubstituted alkenylsilanes could be readily transformed into the corresponding diarylated benzosiloles, which have been proven to be a potential AIE material and a fluorene material.

Recent Advances in Alkenyl sp2 C-H and C-F Bond Functionalizations: Scope, Mechanism, and Applications

Alkenes and their derivatives are featured widely in a variety of natural products, pharmaceuticals, and advanced materials. Significant efforts have been made toward the development of new and practical methods to access this important class of compounds by selectively activating the alkenyl C(sp²)-H bonds in recent years. In this comprehensive review, we describe the state-of-the-art strategies for the direct functionalization of alkenyl sp² C-H and C-F bonds until June 2022. Moreover, metal-free, photoredox, and electrochemical strategies are also covered. For clarity, this review has been divided into two parts; the first part focuses on currently available alkenyl sp² C-H functionalization methods using different alkene derivatives as the starting materials, and the second part describes the alkenyl sp² C-F bond functionalization using easily accessible gem-difluoroalkenes as the starting material. This review includes the scope, limitations, mechanistic studies, stereoselective control (using directing groups as well as metal-migration strategies), and their applications to complex molecule synthesis where appropriate. Overall, this comprehensive review aims to document the considerable advancements, current status, and emerging work by critically summarizing the contributions of researchers working in this fascinating area and is expected to stimulate novel, innovative, and broadly applicable strategies for alkenyl sp² C-H and C-F bond functionalizations in the coming years.

Highly Efficient and Selective Photocatalytic Nonoxidative Coupling of Methane to Ethylene over Pd-Zn Synergistic Catalytic Sites

Photocatalytic nonoxidative coupling of CH4 to multicarbon (C2+) hydrocarbons (e.g., C2H4) and H2 under ambient conditions provides a promising energy-conserving approach for utilization of carbon resource. However, as the methyl intermediates prefer to undergo self-coupling to produce ethane, it is a challenging task to control the selective conversion of CH4 to higher value-added C2H4. Herein, we adopt a synergistic catalysis strategy by integrating Pd-Zn active sites on visible light-responsive defective WO3 nanosheets for synergizing the adsorption, activation, and dehydrogenation processes in CH4 to C2H4 conversion. Benefiting from the synergy, our model catalyst achieves a remarkable C2+ compounds yield of 31.85 μmol·g-1·h-1 with an exceptionally high C2H4 selectivity of 75.3% and a stoichiometric H2 evolution. In situ spectroscopic studies reveal that the Zn sites promote the adsorption and activation of CH4 molecules to generate methyl and methoxy intermediates with the assistance of lattice oxygen, while the Pd sites facilitate the dehydrogenation of methoxy to methylene radicals for producing C2H4 and suppress overoxidation. This work demonstrates a strategy for designing efficient photocatalysts toward selective coupling of CH4 to higher value-added chemicals and highlights the importance of synergistic active sites to the synergy of key steps in catalytic reactions.

Palladium-catalyzed triple coupling of 2-iodoanisoles with aryl iodides to access 6H-dibenzopyrans

A palladium-catalyzed triple coupling of 2-iodoanisoles with aryl iodides has been developed. 3-Methyl-2-pyridone was used as a ligand to accelerate the cross-coupling and suppress the homo-coupling of 2-iodoanisoles. A variety...

Decarboxylative cyclization of o-chlorobenzoic acids with C,C-palladacycles formed by an aminopalladation/dealkylation strategy to access dibenzo[a,c]carbazoles

A novel decarboxylative cyclization of o-chlorobenzoic acids with C,C-palladacycles formed by an aminopalladation/dealkylation strategy for the assembly of dibenzo[a,c]carbazoles has been reported.