[2010年08月09日]

纳米笼微环境的调控催化取得进展

“介孔材料纳米笼中催化”是我组杨恒权博士发展的一种固载金属有机催化剂的新方法(Chem. Commun., 1086-1088, 2007, http://dx.doi.org/10.1039/b614635jGreen Chem. 11, 257 - 264 2009, http://dx.doi.org/10.1039/b815997a)。这一方法主要通过硅烷化的方法将介孔材料孔口尺寸缩小,使金属配合物限域在介孔笼内。根据金属配合物催化剂的尺寸、反应物的尺寸和产物的尺寸大小,通过改变硅烷化试剂链长短可以选择性的调节催化剂的孔口尺寸,使反应物和产物能够自由通过孔口扩散,同时将金属配物限域在笼中。通过这种方法,我们成功的将手性Co(Salen)Ru-TsDPENVO(Salen)配合物组装在SBA-16的纳米笼内,不仅得到了可与均相结果相媲美的催化活性和手性选择性,而且,成功的实现了催化剂循环利用。

    

  不仅如此,将纳米笼内封装Co(Salen)催化剂后,发现通过增加纳米笼内封装催化剂的量,得到的固体催化剂在催化剂用量较低时(S/C=2000~12000),催化活性远高于均相催化剂。这是因为,由于其在环氧化物的水解动力学拆分反应中存在双分子协同催化作用,将Co(Salen)限域在只有5-8 nm的纳米笼内,使得两个催化剂之间的空间范围缩小为均相的1/47,可以更有效地实现双分子协同催化。(Angew. Chem. Int. Ed., 6861-6865 2007 http://dx.doi.org/10.1002/anie.200701747 

最近,我组白诗扬同学等人通过对纳米笼微环境进行调控,选用具有双亲性基团的硅酯和具有亲油性基团的硅酯作为封装和修饰剂,成功的实现了对纳米笼微环境的调控。以Ru-TsDPEN作为模型催化剂,其催化的水相不对称氢转移反应作为模型反应,来表征不同微环境的影响。当纳米笼具有双亲性微环境时,催化剂表现出来的活性是亲油性微环境催化剂的10倍。这一结果证明,我们可以从分子尺寸上实现对纳米笼微环境的调控,来适应不同的催化剂和反应的需要。该结果被选为内封面文章,将发表在近期出版的Chem. Commun.,2010, DOI: 10.1039/c0cc01401j. http://10.1039/c0cc01401j

 

Abstract

Our group ever reported a general method for encapsulation of different transition metal complexes in the nanocage of SBA-16 for asymmetric catalysis. Since there are no covalent linkage and other strong interactions between the complex and the surface of the nanocage, the metal complexes encapsulated in the nanocage keep their catalytic properties as much as possible. Several high performance solid catalysts for asymmetric catalysis were successfully obtained by encapsulating transition metal complex such as Ru-TsDPEN, Co(Salen) and VO(Salen) in the nanocage of SBA-16.

Recently, different silylation reagents were used not only for reducing the pore entrance size but alos for tailoring the microenvironment of the resulted catalyst. Ru-TsDPEN confined in the nanocage with amphiphilic microenvironment can be ten times more active than that with hydrophobic one in the transfer hydrogenation of acetophenone in HCOONa-H2O, which is mainly due to the enhanced diffusion rates of reactants during the catalytic process.

 

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