Characterization of basic catalysts by the use of nitromethane as NMR probe molecule and reactant
作者:E Lima
DOI:10.1016/j.jcat.2003.12.017
日期:2004.4.1
measure of the basic strength. Discussion of NMR and catalytic results takes into account the respective roles of basicity and of conjugate Lewis acidity. Basicity is needed to form a reactive anion comparable to aci-anion nitromethane, but the higher the stabilization of aci-anion nitromethane by Lewis acidity, the lower the activity. Increasing the basic strength by decreasing the Lewis acidity of the
描述了通过使用硝基甲烷反应性吸附的13 C CP / MAS NMR光谱从类水滑石前体获得的混合氧化物的碱度特征。在具有酸碱对的Lewis碱上,吸附物质的性质,即硝基甲烷,阴离子阴离子硝基甲烷和甲磺酸盐类似物,取决于该对上碱性和酸性部位的相对强度。使用布朗斯台德碱(如褐铁矿类型的层状双氢氧化物(LDH))无法获得这些物质。在那种情况下,建议形成甲酸盐类似物。研究了将硝基甲烷迈克尔加成到环己-2-烯-1-酮中的非均相碱催化作用。在催化剂的活性与13的活性之间建立了关系。酰基阴离子硝基甲烷的C CP / MAS NMR化学位移,是碱性强度的量度。NMR和催化结果的讨论考虑了碱度和共轭路易斯酸度的各自作用。需要碱性才能形成可与氰基硝基甲烷媲美的反应性阴离子,但路易斯酸度对阴离子型硝基甲烷的稳定性越高,活性越低。如13 C MAS NMR所示,通过降低酸碱对的Lewis酸度来提高基本强度会导致活性