Application of chiral recyclable catalysts in asymmetric catalysis

Chiral drugs hold a significant position within the contemporary pharmaceutical market, and the chiral catalysts play a crucial role in their synthesis. However, current chiral catalysts encounter challenges pertaining to their separation from products and the recycling process. The utilization of chiral recyclable catalysts not only reduces production costs but also aligns with the growing emphasis on environmentally-friendly chiral synthetic chemistry. These recyclable catalysts exhibit diverse carriers and distinct characteristics. Chemists employ the distinctive attributes of individual carriers to render them recyclable, thereby yielding time and cost savings. This review examines the asymmetric recyclable catalytic reactions reported between January 2017 and October 2023, categorizing them based on carrier solubility, and elucidates the loading techniques, catalytic impacts, recovery approaches, and recycling processes associated with these carriers.

Synergy between homogeneous and heterogeneous catalysis

Catalysis plays a decisive role in the advancement of sustainable processes in chemical, pharmaceutical, and agrochemical industries as well as petrochemical, material, and energy technologies. Notably, more than 80% of...

Metal–organic framework (MOF)-, covalent-organic framework (COF)-, and porous-organic polymers (POP)-catalyzed selective C–H bond activation and functionalization reactions

The review summarizes the state-of-the-art of C–H active transformations over crystalline and amorphous porous materials as new emerging heterogeneous (photo)catalysts.

Controlling Heterogeneous Catalysis with Organic Monolayers on Metal Oxides

ConspectusA key theme of heterogeneous catalysis research is achieving control of the environment surrounding the active site to precisely steer the reactivity toward desired reaction products. One method toward this goal has been the use of organic ligands or self-assembled monolayers (SAMs) on metal nanoparticles. Metal-bound SAMs are typically employed to improve catalyst selectivity but often decrease the reaction rate as a result of site blocking from the ligands. Recently, the use of metal oxide-bound organic modifiers such as organophosphonic acid (PA) SAMs has shown promise as an additional method for tuning reactions on metal oxide surfaces as well as modifying oxide-supported metal catalysts. In this Account, we summarize recent approaches to enhance catalyst performance with oxide-bound monolayers. These approaches include (1) modification of metal oxide catalysts to tune surface reactions, (2) formation of SAMs on the oxide component of supported metal catalysts to modify sites at the metal-support interface, and (3) enhancement of catalyst performance (e.g., stability) through modification of sites remote from the active sites.Both the headgroups and organic tail groups of PA SAMs or other ligands can influence reactions on metal oxide surfaces. Binding of the headgroup can selectively poison certain active sites, altering the selectivity in a manner analogous to metal-bound ligands (at the expense of active site quantity). Moreover, tail groups can be functionalized to interact favorably with reactants and intermediates, for instance through dipole-dipole interactions. On supported metal catalysts like Pt/Al₂O₃, PA SAMs can selectively form on the oxide support. This selective deposition allows for modification of the metal-support interface with minimal blockage of metal sites. PA headgroups were shown to provide tunable acid sites at the interface, dramatically improving hydrodeoxygenation rates of various alcohols. Additionally, organic tail functionality was used to activate or stabilize specific reactants at the interface, such as with the use of amine-functionalized PAs to stabilize chemisorption of CO₂ during the reverse water gas shift reaction. PAs have also been found to affect the electronic properties of bulk metal sites through long-range electron withdrawal via the oxide, providing an additional avenue to tune catalytic behavior. Finally, organic modifiers were shown to enhance catalytic performance without directly modifying the active site. For instance, in biphasic liquid environments the modification of catalyst particles with hydrophobic or hydrophilic SAMs shifts the selectivity of multipath reactions on the basis of the hydrophobicities of different intermediates and products. As another "long-range" effect, the deposition of ligands on oxide supports improved catalyst stability through both improved resistance to sintering and suppression of active site poisoning. The recent contributions discussed in this Account demonstrate the versatility and significant potential for the approach of modifying catalysts with oxide-bound organic monolayers.

Phosphorus containing porous organic polymers: synthetic techniques and applications in organic synthesis and catalysis

The phosphorus-containing porous organic polymer is a trending material for the synthesis of heterogeneous catalysts. Decades of investigations have established phosphines as versatile ligands in homogeneous catalysis. Recently, phosphine-based heterogeneous catalysts were synthesized to exploit the same electronic properties while leveraging extra stability and reusability. In the last few decades, the catalysts were applied in diverse organic transformations, including hydroformylation, hydrogenation, C-C, C-N and C-X coupling, hydrosilylation, oxidative-carbonylation reactions, and so on. However, even though these polymers possess a multifunctional character, they face multiple synthetic issues in controlling the pore size, increasing the surface area, and creating a single type of active site. This review summarizes the developments in this field over the last few decades, highlighting the current limitation and future scope.

Multifunctional chiral cationic porous organic polymers: gas uptake and heterogeneous asymmetric organocatalysis

Chiral porous organic polymers are characterized by robust, non-toxic and recyclable properties. Therefore, compared with small molecular catalysts, they have attracted much attention in the field of heterogeneous asymmetric organic catalysis.