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標題: | 應用固定於介孔SBA-15之不同鏈長掌性脯氨酸衍生物於二乙基鋅對苯甲醛的不對稱加成反應 Mesoporous SBA-15 immobilized Proline-derived ligands with linkers of various lengths in asymmetric diethylzinc addition to benzaldehyde |
作者: | Hsin-chieh Chung 鍾欣潔 |
指導教授: | 鄭淑芬 |
關鍵字: | 介孔材料,不對稱加成,脯氨酸衍生物, SBA15,Proline-derived ligands, |
出版年 : | 2008 |
學位: | 碩士 |
摘要: | 異相觸媒具有許多的優點,像是容易從反應物中分離、可以重覆使用及應用於連續流動的反應系統中等。然而,將高效之掌性催化劑共價接於固體載體後,可能會使得掌性觸媒構形扭曲或是與固體載體之間出現立體阻礙,或是活性中心與載體表面官能基之間出現了負面影響的作用力而降低活性。在本篇論文中嘗試以二乙基鋅對苯甲醛的不對稱加成反應為範例,將高效之掌性脯氨酸衍生物(α,α-diphenyl-L-prolinol)以不同鏈長共價接於高表面積、高穩定性的介孔材料SBA-15載體上。實驗方法上,使用共縮合的方式合成出含硫醇及氯丙基的介孔SBA-15,並利用加長預水解時間或是添加氯化鈉的方式來提高官能基的含量。利用thiol-ene addition將不同碳氫鏈長度之掌性觸媒接至含硫醇的介孔SBA-15上,為了做比較也用親核取代反應將掌性觸媒接至含氯丙基之介孔SBA-15合成出較短碳氫鏈之觸媒,應用於催化反應,證實觸媒的活性確實可經由加長鏈長而變好。文章中也探討添加氯化鈉合成的介孔SBA-15會有較佳的縮合度,並減少載體表面的矽醇基;應用於二乙基鋅對苯甲醛的不對稱加成反應中,發現會明顯提升催化的效果,轉換率及鏡像選擇能力都會變得更佳。其中20%氯丙基的SBA-15(20%Cl(1.5)-t-cata)由於含有較多的掌性proline衍生物反應24小時即可到達82%的轉化率及74%的ee值,是本論文中效果最佳之觸媒。若是比較TON,則最佳值應為10%硫醇基以八個碳鏈長的方式接上掌性proline衍生物的觸媒(10%SH(1.5)-t-8Ccata),其TON可達25.4/day,並有68%的ee值。 The main advantages of heterogeneous catalysts are the easy separation of the catalyst from the reaction mixture, allowing the recovery and reuse of the catalyst, and the possibility of continuous-flow operation. However, covalent anchoring a highly enantioselective catalyst to a solid support usually results in a significant loss of its activity and asymmetric induction capability in comparison to that of the homogeneous phase, attributed to the sterical hindrances of the catalytic site and the interaction between the active sites and the surface of the support. In the present study, chiral proline derivatives with linkers of various lengths were anchored to mesoporous silica SBA-15. Thiol-functional mesoporous SBA-15 (SH-SBA-15) was prepared by one-pot co-precipitation method. With the aid of NaCl salt, the silicate condensation was more complete and the residual silanol groups on the silica surface were reduced. Besides, the addition of NaCl salt in the initial mixture greatly enhanced the ordering of the mesostructure and the stabilities of the mesoporous materials. Vinyl-substituted chiral proline derivatives were then attached to SH-SBA-15 through AIBN-mediated radical addition of SH groups to C=C bonds. The resultant materials were examined as the catalysts in asymmetric diethylzinc addition to benzaldehyde reaction. The catalytic activity and chiral selectivity indeed increased progressively with the length of the tether linking the ligand to the silica surface. Moreover, the e.e. values and the conversions were obviously better over the mesoporous materials synthesized with NaCl than that without NaCl. The highest enantioselectivity of 74% and conversion of 82% was achieved using catalyst 20%Cl(1.5)-t-cata, attributed to the highest content of active sites. If comparison is based on the TON value, catalyst 10%SH(1.5)-t-8Ccata has the best performance (25.4/day), 68% ee and 75% conversion can be achieved. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/40812 |
全文授權: | 有償授權 |
顯示於系所單位: | 化學系 |
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