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四、Ln~(3+)在有机合成中的应用 Ln~(3+)的无机盐是一种比较便宜的镧系化合物。它具有Lewis酸性,能与一些带孤对电子(带o:,C=O:,—N:,S:,—P=O:,S=O:,—P:基团)的化合物发生络合作用。根据硬软酸碱理论(HSAB),它属于硬酸,酸度在Ti~(4+)和Sc~(3+)之间,(Mg~(2+)>Ca~(2+)>Sr~(2+)>Sc~(3+)>La~(3+)>Ce~(4+)>Ti~(4+)),生成的络合物基本上是离子性的,f轨道很少参与成键。Ln~(3+)具有较大的配位数,最大可达12。基于这些特性,对Ln~(3+)催化以及改进还原反应的选择性进行了研究。 (一)、作为有机合成中的催化剂 1.Lewis酸性的反应 (1) 催化环氧化物重排成酮,提高立体选择性
Fourth, Ln ~ (3 +) in the application of organic synthesis Ln ~ (3 +) inorganic salts is a cheaper lanthanide compounds. It has the Lewis acidity and can react with some compounds with lone pairs of electrons (with O, C = O, N, S, P, O, Cooperation. According to the theory of hard and soft acids and bases (HSAB), it belongs to the hard acid with the acidity between Ti ~ (4+) and Sc ~ (3+), Mg ~ (2 +)> Ca ~ (2 +)> Sr ~ (2 +)> Sc ~ (3 +)> La ~ (3 +)> Ce ~ (4 +)> Ti ~ (4+)), the resulting complexes are essentially ionic and the f orbitals are few Participate in the key. Ln ~ (3 +) has a larger number of coordination, up to 12. Based on these characteristics, the selectivity of Ln ~ (3+) catalysis and the reduction reaction were studied. (A), as a catalyst in organic synthesis 1.Lewis acidic reaction (1) catalytic epoxy rearrangement into ketones, improve the stereoselectivity