Rhodium-Iodide Complex on a Catalytically Active SiO2 Surface for One-Pot Hydrosilylation-CO2 Cycloaddition

In this study, a novel Rh-iodide complex was synthesized through a surface reaction between an immobilized Rh cyclooctadiene complex and alkylammonium iodide (N⁺ I^- ) on SiO₂ . In the presence of ammonium cations, the SiO₂ -supported Rh-iodide complex could be effectively used for the one-pot synthesis of various silylcarbonate derivatives starting from epoxy olefins, hydrosilanes, and CO₂ . The maximum turnover numbers (TONs) for the hydrosilylation reaction and the CO₂ cycloaddition were 7600 (Rh) and 130 (N⁺ I^- ), respectively. The catalyst exhibited much higher performance for hydrosilylation than solely the Rh complex on SiO₂ . The mechanism of the Rh-catalyzed hydrosilylation reaction and the local structure of Rh, which is affected by the co-immobilized N⁺ I^- , were investigated by using Rh and I K-edge XAFS and XPS. Analysis of the XAFS profiles indicated the presence of a Rh-I bond. The Rh unit was in its electron-rich state. Curve-fitting analysis of the Rh K-edge EXAFS profiles suggests dissociation of the cycloocta-1,5-diene (COD) ligand from the Rh center. Results from spectroscopic and kinetic analyses revealed that the high activity of the catalyst (during hydrosilylation) could be attributed to a decrease in steric hindrance and the electron-rich state of the Rh. The decrease in the steric hindrance could be attributed to the absence of COD, and the electron-rich state promoted the oxidative addition of Si-H. To the best of our knowledge, this is the first example of a one-pot silylcarbonate synthesis as well as a determination of a novel surface Rh-iodide complex and its catalysis.

Hollow-Shell-Structured Mesoporous Silica-Supported Palladium Catalyst for an Efficient Suzuki-Miyaura Cross-Coupling Reaction

The construction of a high stability heterogeneous catalyst for privileged common catalysis is a benefit in regard to reuse and separation. Herein, a palladium diphenylphosphine-based hollow-shell-structured mesoporous catalyst (HS@PdPPh2@MSN) was prepared by immobilizing bis((diphenylphosphino)ethyltriethoxysilane)palladium acetate onto the inner wall of a mesoporous organicsilicane hollow shell, whose surface was protected by a –Si(Me)3 group. Electron microscopies confirmed its hollow-shell-structure, and structural analyses and characterizations revealed its well-defined single-site active species within the silicate network. As presented in this study, the newly constructed HS@PdPPh2@MSN enabled an efficient Suzuki-Miyaura cross-coupling reaction for varieties of substrates with up to 95% yield in mild conditions. Meanwhile, it could be reused at least five times with good activity, indicating its excellent stability and recyclability. Furthermore, the cost-effective and easily synthesized HS@PdPPh2@MSN made it a good candidate for employment in fine chemical engineering.

Ru-Pd Thermoresponsive Nanocatalyst Based on a Poly(ionic liquid) for Highly Efficient and Selectively Catalyzed Suzuki Coupling and Asymmetric Transfer Hydrogenation in the Aqueous Phase

The development of intelligent polymeric materials to precisely control the catalytic sites of heterogeneous catalysts and enable highly efficient catalysis of a cascade reaction is of great significance. Here, the utilization of a polymer ionic liquid (PIL) containing two different anions facilitates the preparation of Ru-Pd catalysts with controllable phase transition temperatures and hydrophilic and hydrophobic surfaces. The combined multifunctionality, synergistic effects, micellar effects, aggregation effects, and temperature responsiveness of the nanocatalyst render it suitable for promoting selectively catalyzed Suzuki coupling and asymmetric transfer hydrogenation in water. Above the lower critical solution temperature (LCST) of the catalyst, it catalyzes only the coupling reaction with a high turnover number (TON) of up to 999.0. Below the LCST, the catalyst catalyzes only the asymmetric transfer hydrogenation with good catalytic activity and enantioselectivity. It is important that the catalyst can be simply and effectively recovered and recycled at least 10 times without significant loss of catalytic activity and enantioselectivity. This study also highlights the superiority of multifunctional heterogeneous catalysts based on PILs, which not only overcome limitations associated with low activity of heterogeneous catalysts but also realize selective reactions according to a temperature change, thereby improving the reactivity and enantioselectivity in multiple organic transformations.

Heterogeneous Synergistic Catalysis for Promoting Aza-Michael–Henry Tandem Reaction for the Synthesis of Chiral 3-Nitro-1,2-Dihydroquinoline

Heterogeneous synergistic catalysis by SBA-15 immobilized chiral amines catalysts has promoted efficient aza-Michael–Henry tandem reaction for the synthesis of chiral 3-Nitro-1,2-Dihydroquinoline. Final products in the asymmetric aza-Michael–Henry cascade reactions between 2-aminobenzaldehyde and β-nitrostyrolene were afforded in a yield of 85% and an enantiomeric excess (ee) value of 98% on (S)-(–)-2-aminomethyl-1-ethylpyrrolidine immobilized SBA-15. SBA-15-AEP catalyst has been also extended to the asymmetric aza-Michael–Henry cascade reaction of substituted R1-2-aminobenzaldehyde and R2-substituted nitroolefin. The heterogeneous synergistic mechanism for both tertiary amine and secondary amine immobilized mesoporous has been proposed in detail including the geometrical constraints in the ee promotion.

Pyrrolidine-based chiral porous polymers for heterogeneous organocatalysis in water

The “bottom-up” reticulation of chiral pyrrolidine into POPs for heterogeneous organocatalysis in pure water.

Asymmetric one-pot reactions using heterogeneous chemical catalysis: recent steps towards sustainable processes

Asymmetric one-pot reactions applying heterogeneous chemical catalysts and unifying the benefits of these catalytic materials with the advantages of one-pot methods, are surveyed.

Heterogeneous enantioselective synthesis of chromans via the oxa-Michael–Michael cascade reaction synergically catalyzed by grafted chiral bases and inherent hydroxyls on mesoporous silica surface

A heterogeneous enantioselective oxa-Michael–Michael reaction for the synthesis of chromans has been developed on bifunctional catalysts, resulting in excellent catalytic performance.

Direct Estimation of the Surface Location of Immobilized Functional Groups for Concerted Catalysis Using a Probe Molecule

The location of active sites during concerted catalysis by a metal complex and tertiary amine on a SiO2 surface is discussed based on the interaction between the functionalized SiO2 surface and a probe molecule, p-formyl phenylboronic acid. The interactions of the probe molecule with the surface functionalities, diamine ligand, and tertiary amine, were analyzed by FT-IR and solid-state (13)C and (11)B MAS NMR. For the catalyst exhibiting high 1,4-addition activity, the diamine ligand and tertiary amine base exist in closer proximity than in the catalyst with low activity.

Yolk–shell-structured mesoporous silica: a bifunctional catalyst for nitroaldol–Michael one-pot cascade reaction

A site-isolated yolk–shell-structured mesoporous silica for the nitroaldol–Michael one-pot enantio-relay reaction to convert aldehydes, nitromethane and acetylacetone to chiral diones is developed.

Design and fabrication of mesoporous heterogeneous basic catalysts

Recent advances in mesoporous solid bases were reviewed, and fundamental principles of how to fabricate efficient basic catalysts were highlighted.

Nanoporous silica-supported organocatalyst: a heterogeneous and green hybrid catalyst for organic transformations

Organically modified hybrid silica mesostructures are becoming increasingly promising candidates as catalysts for various kinds of organic reactions and green chemistry.