Understanding Anionic “Ligandless” Palladium Species in the Mizoroki–Heck Reaction

Asymmetric Total Synthesis of Anti-HBV Drug Entecavir: Catalytic Strategies for the Stereospecific Construction of Densely Substituted Cyclopentene Cores

We have successfully accomplished a catalytic asymmetric total synthesis of entecavir, a first-line antihepatitis B virus medication. The pivotal aspect of our strategy lies in the utilization of a Pd-catalyzed enyne borylative cyclization reaction, enabling the construction of a highly substituted cyclopentene scaffold with exceptional stereoselectivity. Additionally, we efficiently accessed the crucial 1,3-diol enyne system early in our synthetic route through a diarylprolinol organocatalyzed enantioselective cross-aldol reaction and Re-catalyzed allylic alcohol relocation. By strategically integrating these three catalytic protocols, we established a practical pathway for acquiring valuable densely heteroatom-substituted cyclopentene cores.

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

Being negative can be positive: metal oxide anions promise more selective methane to methanol conversion

Computational studies are performed to show that metal oxide anionic complexes promote the CH₄ + N₂O → CH₃OH + N₂ reaction with low activation barriers for the C-H activation and the formation of the CH₃-OH bond. The energy for the release of the produced methanol is minimal, reducing the residence time of methanol around the catalytic center and preventing its overoxidation.

A general synthesis of aromatic amides via palladium-catalyzed direct aminocarbonylation of aryl chlorides

Aryl amines made easy by palladium-catalyzed aminocarbonylation of aryl chlorides.

Dual Nickel/Photoredox-Catalyzed Deaminative Cross-Coupling of Sterically Hindered Primary Amines

We report a method to activate α-3° amines for deaminative arylation via condensation with an electron-rich aldehyde and merge this reactivity with nickel metallaphotoredox to generate benzylic quaternary centers, a common motif in pharmaceuticals and natural products. The reaction is accelerated by added ammonium salts. Evidence is provided in support of two roles for the additive: inhibition of nickel black formation and acceleration of the overall reaction rate. We demonstrate a robust scope of amine and haloarene coupling partners and show an expedited synthesis of ALK2 inhibitors.

Ionic Pd/NHC Catalytic System Enables Recoverable Homogeneous Catalysis: Mechanistic Study and Application in the Mizoroki-Heck Reaction

N-Heterocyclic carbene (NHC) ligands are ubiquitously utilized in catalysis. A common catalyst design model assumes strong M-NHC binding in this metal-ligand framework. In contrast to this common assumption, we demonstrate here that lability and controlled cleavage of the M-NHC bond (rather than its stabilization) could be more important for high-performance catalysis at low catalyst concentrations. The present study reveals a dynamic stabilization mechanism with labile metal-NHC binding and [PdX₃ ]^- [NHC-R]⁺ ion pair formation. Access to reactive anionic palladium intermediates formed by dissociation of the NHC ligands and plausible stabilization of the molecular catalyst in solution by interaction with the [NHC-R]⁺ azolium ion is of particular importance for an efficient and recyclable catalyst. These ionic Pd/NHC complexes allowed for the first time the recycling of the complex in a well-defined form with isolation at each cycle. Computational investigation of the reaction mechanism confirms a facile formation of NHC-free anionic Pd in polar media through either Ph-NHC coupling or reversible H-NHC coupling. The present study formulates novel ideas for M/NHC catalyst design.

Energy Decomposition Analyses Reveal the Origins of Catalyst and Nucleophile Effects on Regioselectivity in Nucleopalladation of Alkenes

Nucleopalladation is one of the most common mechanisms for Pd-catalyzed hydro- and oxidative functionalization of alkenes. Due to the electronic bias of the π-alkene-palladium complexes, nucleopalladations with terminal aliphatic alkenes typically deliver the nucleophile to the more substituted sp² carbon to form the Markovnikov-selective products. The selective formation of the anti-Markovnikov nucleopalladation products requires the inherent electronic effects to be overridden, which is still a significant challenge for reactions with simple aliphatic alkenes. Because the interactions between the nucleophile and the alkene substrate are influenced by a complex combination of multiple types of steric and electronic effects, a thorough understanding of the interplay of these underlying interactions is needed to rationalize and predict the regioselectivity. Here, we employ an energy decomposition approach to quantitatively separate the different types of nucleophile-substrate interactions, including steric, electrostatic, orbital interactions, and dispersion effects, and to predict the impacts of each factor on regioselectivity. We demonstrate the use of this approach on the origins of catalyst-controlled anti-Markovnikov-selectivity in Hull's Pd-catalyzed oxidative amination reactions. In addition, we evaluated the regioselectivity in a series of nucleopalladation reactions with different neutral and anionic Pd catalysts and N- and O-nucleophiles with different steric and electronic properties. On the basis of these computational analyses, a generalized scheme is established to identify the dominant nucleophile-substrate interaction affecting the regioselectivity of nucleopalladations with different Pd catalysts and nucleophiles.