【作者】 于凯；

【导师】 刘双喜；

【作者基本信息】 南开大学 ， 材料物理与化学， 2008， 博士

【摘要】 随着全世界对手性产品需求的日益增长,手性化合物的高效、绿色生产方法已受到普遍关注。在各种生产手性化合物的方法中,手性催化是最符合原子-经济观点的。相对于均相手性催化,非均相手性催化由于其易于产品分离、催化剂可以重复利用等优点,成为手性催化领域的研究热点。烯烃的不对称环氧化反应是制备光学活性环氧化物的重要途径,在医药、农药、香料等精细化学品的合成上具有非常重要的意义。由于salen Mn(III)化合物在非官能团化烯烃的不对称环氧化反应中表现出的高催化活性和对映选择性,近年来关于salen Mn(III)化合物在无机介孔材料上的固载化研究受到了广泛的关注。在目前报道的固载研究中,大多数非均相salen Mn(III)催化剂都只得到了比相应均相催化剂低的催化活性和对映选择性,只有一小部分工作获得了与均相催化剂相当甚至更高的对映选择性,这被普遍地归结为载体孔道空间限阈效应的影响。然而系统地研究载体空间限阈效应对非均相手性催化剂催化性能的影响还很少见报道。本文旨在通过详细考察载体的孔道结构、孔径以及活性组分的分布状态对非均相salen Mn(III)催化剂催化性能的影响,从而更深入地了解载体孔道空间限阈效应对非均相手性催化剂催化性能的影响规律。本文采用具有不同碳链长度的季铵盐型表面活性剂为模板剂合成了一系列孔径在小范围内变化的MCM-41与MCM-48介孔材料,并通过不同的有机硅烷固载了三种不同结构的salen Mn(III)化合物。XRD、FT-IR、DR UV-Vis、N2吸附-脱附、元素分析和ICP-AES表征的结果表明,salen Mn(III)化合物被成功固载在了介孔载体的孔道中,并且最后制得的非均相催化剂都保持了载体的特征孔道结构。所合成的非均相salen Mn(III)催化剂在非官能团化烯烃的不对称环氧化反应中表现出了高的催化活性和对映选择性。并且通过研究发现,载体孔径的精细调变能明显影响非均相催化剂的催化性能。通常情况下,固载在较大孔径载体上的非均相催化剂能够得到较高的催化活性;而当载体孔径与底物分子大小相匹配时,非均相催化剂能够得到较高的对映选择性。本文考察了有机硅烷在介孔载体上的负载量对非均相salen Mn(III)催化剂催化性能的影响规律,从而确定了不同结构的salen Mn(III)化合物固载在不同介孔载体上的最佳有机硅烷投料量。同时实验结果表明,有机硅烷的负载量对催化剂催化性能以及活性组分稳定性都有明显的影响。较高的有机硅烷负载量能提高催化剂的稳定性,催化剂中活性组分不易流失,但同时也增加了反应物与产物扩散的阻力,从而造成催化剂的催化性能降低。本文采用共缩聚法制备了活性组分在介孔载体表面分布更加均匀的非均相salen Mn(III)催化剂。通过含salen Mn(III)结构的桥连有机硅烷与正硅酸乙酯共缩聚制备得到了活性组分分布更为均匀的PMOs材料,不过由于活性组分被部分包埋在孔壁中,从而使得催化剂的催化性能较低。为此又通过3-氨丙基-三乙氧基硅烷与正硅酸乙酯共缩聚制备了有机官能团化的介孔材料,并将其用于固载salen Mn(III)化合物。通过实验考察了有机硅烷的负载量对催化剂催化性能的影响,从而确定了3-氨丙基-三乙氧基硅烷的最佳投料量。由此制备得到的非均相salen Mn(III)催化剂即使在较低的用量下(0.6mol%)仍然能在烯烃的不对称环氧化反应中表现出与均相催化剂相当的催化活性和对映选择性,催化剂的催化效率大大提高。同时本文还采用多步移植法制备了无机介孔材料固载的非均相salen Mn(III)催化剂。该方法操作简便,并可用于固载不对称结构的手性salen Mn(III)化合物。所制备的非均相催化剂在α-甲基苯乙烯的不对称环氧化反应中得到了>99.9%的反应ee值,明显高于均相催化剂的ee值49.8%。同时催化剂在茚和1-苯基环己烯的不对称环氧化反应中表现出了与均相催化剂相当的催化活性和对映选择性。所合成的非均相催化剂具有较好的稳定性,可以被重复使用三次以上。更多还原

【Abstract】 With the increasing demand for chiral products around the world, the efficient and green production method for chiral compounds has been widely concerned. Among the various methods to selectively produce single enantiomer, asymmetric catalysis is undoubtedly the most attractive one from the atom-economic point of view. Compared with the homogeneous asymmetric catalysis system, the heterogeneous one has the advantages of easy catalyst/product separation and simple catalyst recycling. And more and more interests have been focused on the studies of heterogenization of chiral complexes. The asymmetric epoxidation of unfunctionalized olefins is an important approach for synthesizing optically active epoxides, and thus is widely used in the synthesis of fine chemicals, such as pharmaceuticals, agrochemicals and perfumes. Chiral salen Mn(III) complexes have demonstrated activity and selectivity for the enantioselective epoxidation of unfunctionalized olefins under homogeneous condition. In recent years, the immobilization of chiral salen Mn(III) complexes on inorganic mesoporous materials has received much attention due to the advantages of heterogeneous catalysis systems.In most cases, the heterogenized chiral salen Mn(III) catalysts led to lower activity and enantioselectivity compared with the homogeneous counterparts for asymmetric epoxidation, and only a few immobilized catalysts exhibited comparable or even higher ee values than the homogeneous ones. The improvement of enantioselectivity was mainly attributed to the confinement effect of the nanopores. However, the effect of confinement effect on the catalytic performance of mesoporous material-supported chiral salen Mn(III) catalyst has seldom been systemically investigated for the asymmetric epoxidation. In this thesis, the effects of the pore structure and pore size of mesoporous supports and the distribution of active sites on activity and enantioselectivity of the heterogeneous catalysts were studied. And this study would be helpful for further understanding the confinement effect of the nanopores on the catalytic performance of heterogeneous chiral salen Mn(III) catalysts.A series of mesoporous MCM-41 and MCM-48 materials with different pore sizes were synthesized applying the alkylammonium salts with different alkyl chain lengths as templates. These materials were used as supports to immobilize three types of chiral salen Mn(III) complexes via organosilane modification. The results of XRD, FT-IR, DR UV-Vis, N2 sorption, elemental analysis and ICP-AES showed that the chiral salen Mn(III) complexes have been successfully immobilized inside the channels of mesoporous materials, and the heterogeneous catalysts maintain the characteristic mesoporous structures of corresponding parent supports. The as-synthesized heterogeneous chiral salen Mn(III) catalysts were highly active and enantioselective in the asymmetric epoxidation of unfunctionalized olefins. It is found that the catalytic performance of heterogeneous catalysts was closely correlated to the pore sizes of parent supports. Normally, the larger pore size of the supports was beneficial to obtain higher catalytic activity, and the compatible pore size with substrate would be responsible for the improved enantioselectivity in the olefin epoxidation.The influence of organosilane dosage on the catalytic performance of heterogeneous chiral salen Mn(III) catalysts was studied, and the optimum organosilane dosage for the preparation of heterogeneous catalysts was determined. The experiments revealed that the dosage of organosilane had a great effect on the catalytic performance of heterogeneous catalysts and the stability of active species. The higher content of organosilane would improve the stability of the catalysts and decrease the leaching of active sites, however, it could also increase the diffusional resistance of reactants to the active sites located on the inner surfaces of supports, and thus decrease the catalytic performance of heterogeneous catalysts.The co-condensation method was applied to immobilize the chiral salen Mn(III) complex so as to make the active species uniformly dispersed on the surface of supports. The heterogeneous catalysts (PMOs) were prepared through the co-condensation of TEOS and bridged organosilane precursor-containing salen Mn(III) complex. The as-synthesized catalysts showed low activity and enantioselectivity in the epoxidation of olefins due to the embedment of active species into the pore wall. In consideration of this, the organo-functionalized mesoporous materials were prepared by the co-condensation of TEOS and 3-aminopropyltriethoxysilane, and used to immobilize the chiral salen Mn(III) complex. The effects of organosilane dosage on the catalytic performance were studied, thus the optimum dosage of 3-aminopropyltriethoxysilane was presented. The prepared heterogeneous catalysts exhibited comparable activity and enantioselectivity to those of homogeneous counterparts for the epoxidation of unfunctionalized olefins, even at lower dosage of catalysts (0.6mol%), thus providing the greatly increased catalytic efficiency.In addition, the multi-step grafting method was also used to immobilize the chiral salen Mn(III) complexes on inorganic mesoporous materials. This method is simple and can be applied to immobilize unsymmetrical chiral salen Mn(III) complexes. The as-synthesized heterogeneous catalyst exhibited excellent enantioselectivity (>99.9% ee) than homogeneous catalyst (49.8% ee) for the epoxidation ofα-methylstyrene. Moreover, these catalysts obtained comparable activity and enantioselectivity to those of homogeneous counterparts for the epoxidation of indene and 1-phenylcyclohexene. The heterogeneous catalysts were stable and could be recycled three times without loss of enantioselectivity.更多还原