Polymer and Silica Supported Tridentate Schiff Base Vanadium Catalysts for the Asymmetric Oxidation of Ethyl Mandelate - Activity, Stability and Recyclability
作者:Rebecca A. Shiels、Krishnan Venkatasubbaiah、Christopher W. Jones
DOI:10.1002/adsc.200800486
日期:——
The effects of support material, synthesis procedure, and reaction solvent are examined to probe the utility of these catalysts. Linear poly(styrene) supported catalysts are partially soluble under the reaction conditions, and it is shown that the soluble species contribute significantly to the catalytic reactivity. Insoluble catalysts based on the same vanadyl complexes supported on cross-linked poly(styrene)
已知衍生自水杨醛和叔亮氨酸醇或叔亮氨酸的均相三齿席夫碱钒催化剂是用于α-羟基酯(包括扁桃酸乙酯)的不对称氧化的优异催化剂。在此,合成了新的类似的负载型,半可溶性和不溶性催化剂,并报道了它们相对于均相催化剂的活性。新型催化剂的特点是1 H和13C NMR光谱,质谱(EI,ESI,FAB),X射线晶体学,元素分析,凝胶渗透色谱(GPC),傅立叶变换红外(FT-IR)光谱和氮物理吸附。研究了载体材料,合成步骤和反应溶剂的影响,以探讨这些催化剂的用途。线性聚(苯乙烯)负载的催化剂在反应条件下是部分可溶的,并且表明可溶物质对催化反应性有显着贡献。基于负载在交联聚(苯乙烯)树脂或中孔二氧化硅上的相同钒基络合物的不溶催化剂可实现催化剂的回收和循环利用,在多个反应循环中显示出同等的选择性。介孔二氧化硅负载的催化剂显示出比类似的均相和聚合物负载的催化剂更高的选择性。严格的循环研究表明,每个循环中都有活性损失