製備L-proline官能基化的SBA-15及其在不對稱Aldol加成反應的應用

Abstract

L-Proline包括其衍生物已被大量應用在不對稱Aldol加成反應。異相觸媒具有容易從反應物中分離、可以重複使用等優點。我們將L-proline的結構修飾成帶有SH官能基，與帶有Vinyl官能基的中孔洞材料SBA-15 (Vinyl-SBA-15)，利用AIBN當作起始劑，進行thiol-ene自由基加成反應而可將proline結構固定在中孔洞材料內表面上，達到將proline異相化的目的。有機化合物Cis-4-mercapto-L- proline (SH-proline)乃由 trans-4-hydroxy-L-proline經一系列修飾而得；含Vinyl官能基的SBA-15乃由三區塊共聚物(P123)作為模板試劑，將tetraethyl orthosilicate (TEOS)、vinyltrimethoxysilane (VTMS)在酸性環境下進行水解與共縮合反應，XRD顯示孔洞具有良好排列的二維六角堆積結構。氮氣吸脫附恆溫曲線圖顯示材料的BET比表面積、孔洞體積、與孔徑在SH-proline鍵結在SBA-15表面上後下降，表示有機物存在孔洞中；硫的K-edge光譜圖顯示材料有C-S-C鍵的存在，顯示SH-proline與Vinyl-SBA-15是以共價鍵鍵結，13C CP/MAS NMR光譜圖亦顯示材料含有proline結構，SEM與TEM圖顯示材料的外觀與孔洞性不隨proline的引入而改變。將含有proline結構的SBA-15觸媒應用在不對稱Aldol加成反應時，我們發現觸媒經不同pH水溶液前處理、反應溶劑及溫度對反應的轉化率及鏡像選擇率有重大的影響。

L-Proline is known as an organocatalyst for asymmetric Aldol reaction. For the purpose of easy separation and reuse of the catalyst, L-proline was immobilized onto mesoporous silica to form heterogeneous catalyst through thiol-ene addition using AIBN as the initiator. Cis-4-mercapto-L- proline (SH-proline) was synthesized from trans-4-hydroxy-L-proline. Vinyl group functionalized SBA-15 (briefly termed vinyl-SBA-15) was prepared by co-condensation of tetraethyl orthosili- cate (TEOS) and vinyltrimethoxysilane (VTMS) using P123 copolymer as the pore directing agent in strong acidic environment. XRD patterns showed that the materials contained well-ordered mesopores arranged in 2-D hexagonal arrays. N2 sorption data showed their surface area, pore volume, and pore diameter decreased after L-proline was immobilized. Sulfur K-edge XANES spectra showed the existence of C-S-C bond. 13C CP/MAS solid state NMR showed the existence of proline structure. SEM and TEM images showed the morphologies and mesoporosity didn’t change after poline was immobilized. The SBA-15 immobilized L-proline materials were used as catalysts in the asymmetric Aldol reaction. The pH value of pre-treatment solution, reaction solvent, and temperature were found to affect the chiral selectivity drastically.