Huh Seong, Chen Hung-Ting, Wiench Jerzy W, Pruski Marek, Lin Victor S-Y
Department of Chemistry and Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA.
J Am Chem Soc. 2004 Feb 4;126(4):1010-1. doi: 10.1021/ja0398161.
A series of bifunctionalized mesoporous silica nanosphere-based (MSN) heterogeneous catalysts for the nitroaldol (Henry) reaction have been synthesized. A common 3-[2-(2-aminoethylamino)ethylamino]propyl (AEP) primary group and three different secondary groups, ureidopropyl (UDP), mercaptopropyl (MP), and allyl (AL) functionalities, were incorporated to these mesoporous silica materials by introducing equal amounts of AEP-trimethoxysilane with UDP-, MP-, or AL-trialkoxysilane precursors to our previously reported co-condensation reaction. Structures and relative concentrations of the functional groups were detailed by solid-state NMR and other spectroscopic techniques. The AEP group served as a catalyst, and the other secondary groups provided different noncovalent interactions to reactants and thereby controlled the reaction selectivity. By varying the secondary group in these bifunctionalized MSN catalysts, we investigated the selectivity of a nitroaldol reaction of two competing benzaldehydes reacting with nitromethane by measuring the molar ratio of the nitroalkene products. The selectivity of the bifunctionalized MSN catalysts could be systematically tuned simply by varying the physicochemical properties of the pore surface-bound secondary groups, i.e., polarity and hydrophobicity.
已合成了一系列用于硝基羟醛（亨利）反应的双功能化介孔二氧化硅纳米球基（MSN）多相催化剂。通过将等量的AEP-三甲氧基硅烷与UDP-、MP-或AL-三烷氧基硅烷前驱体引入我们先前报道的共缩合反应中，将常见的3-[2-(2-氨基乙氨基)乙氨基]丙基（AEP）伯胺基团和三种不同的仲胺基团，即脲丙基（UDP）、巯基丙基（MP）和烯丙基（AL）官能团，引入到这些介孔二氧化硅材料中。通过固态核磁共振和其他光谱技术详细研究了官能团的结构和相对浓度。AEP基团作为催化剂，其他仲胺基团为反应物提供不同的非共价相互作用，从而控制反应选择性。通过改变这些双功能化MSN催化剂中的仲胺基团，我们通过测量硝基烯烃产物的摩尔比，研究了两种竞争性苯甲醛与硝基甲烷的硝基羟醛反应的选择性。只需改变孔表面结合的仲胺基团的物理化学性质，即极性和疏水性，就可以系统地调节双功能化MSN催化剂的选择性。
