New Mesoporous Silica-Supported Organocatalysts Based on (2S)-(1,2,4-Triazol-3-yl)-Proline: Efficient, Reusable, and Heterogeneous Catalysts for the Asymmetric Aldol Reaction

Abstract

Novel organocatalytic systems based on the recently developed (S)-proline derivative (2S)-[5-(benzylthio)-4-phenyl-(1,2,4-triazol)-3-yl]-pyrrolidine supported on mesoporous silica were prepared and their efficiency was assessed in the asymmetric aldol reaction. These materials were fully characterized by FT-IR, MS, XRD, and SEM microscopy, gathering relevant information regarding composition, morphology, and organocatalyst distribution in the doped silica. Careful optimization of the reaction conditions required for their application as catalysts in asymmetric aldol reactions between ketones and aldehydes afforded the anticipated aldol products with excellent yields and moderate diastereo- and enantioselectivities. The recommended experimental protocol is simple, fast, and efficient providing the enantioenriched aldol product, usually without the need of a special work-up or purification protocol. This approach constitutes a remarkable improvement in the field of heterogeneous (S)-proline-based organocatalysis; in particular, the solid-phase silica-bonded catalytic systems described herein allow for a substantial reduction in solvent usage. Furthermore, the supported system described here can be recovered, reactivated, and reused several times with limited loss in catalytic efficiency relative to freshly synthesized organocatalysts.

Production of fine chemicals using microporous and mesoporous heterogeneous catalysts

“…The use of (organo)silica-based catalysts offers a substantial reduction in the requirement of a solvent during its use in reactions, as explored during the analysis of the Asymmetric Aldol Reaction [18]. Further to this, this study determined that the silica-based catalyst structure used can be recovered and reused several times with reactivation, providing a minimal loss of activity regarding traditionally used fresh organocatalysts.…”

“…In many cases, high production costs pose a roadblock to more elaborate and in-depth research, resulting in discouragement of their use, particularly when more cost-efficient catalyst structures exist. It is also possible to develop a hybrid-synthetic approach, using both methods, as described by [18]. This paper determined the best catalyst for the use of a silica-based structure under solvent-free conditions with the addition of an acid, a commonly used additive during the synthesis of catalysts.…”

A Comprehensive Review of Fine Chemical Production Using Metal-Modified and Acidic Microporous and Mesoporous Catalytic Materials

“…Their larger pore size often results in the easier embedding of functional groups and guest species, providing a high level of customisability in terms of their catalytic performance. Additionally, the use of (organo) silica-based catalysts offers a substantial reduction in the requirement of a solvent during its use in reactions, as explored during the analysis of the asymmetric aldol reaction [18]. Moreover, this study determined that the silica-based catalyst structure used can be recovered and reused several times with reactivation, providing a minimal loss of activity regarding traditionally used fresh organocatalysts.…”

“…It is also possible to develop a hybrid-synthetic approach, using both methods, as described by Ref. [18]. This paper determined the best catalyst for the use of a silica-based structure under solvent-free conditions, with the addition of an acid, a commonly used additive during the synthesis of catalysts.…”

Fractal Features of the Catalytic Performances of Bimodal Mesoporous Silica‐Supported Organocatalysts Derived from Bipyridine‐Proline for Asymmetric Aldol Reaction

“…For these reasons, a main goal of heterogeneous catalysis research is that the active species are introduced on the appropriate supports, and therefore their stereoselectivity can be utilized to generate the high enantiomeric excess form of the desired product. Hence, several heterogeneous proline-immobilized catalysts have been explored presently, the commonly used supports include polymers, [22,23] ionic liquid, [24] metal-organic frameworks (MOFs), [25] as well as mesoporous organosilica nanoparticles, [26,27] and zeolites. [28] However, as already mentioned, silica-based with well-ordered mesoporous nanomaterials (including MCM-41 [29][30][31] and SBA-15 [32][33][34] ) can be used as more attractive supports for immobilization of proline-based catalysts by the formation of either covalent bond or noncovalent attachment, [35,36] owing to their abundant hydroxyl groups, extremely large surface area and pore volume, uniform and stable pore structure, as well as chemical inertness, excellent thermal and mechanical stability in comparison with organic hosts.…”