Catalysis of the Michael addition reaction by late transition metal complexes of BINOL-derived salens
Catalysis of the Michael addition reaction by late transition metal complexes of BINOL-derived salens
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DOI：
10.1021/jo025993t
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发表时间：
2003-03-07
影响因子：
3.6
通讯作者：
Kozlowski, MC
中科院分区：
文献类型：
--
作者：
Annamalai, V;DiMauro, EF;Kozlowski, MC
合成了Salen金属配合物，并通过X射线晶体学对其进行了表征。X-射线衍射结构表明，这类新的Ni-BINOL-salen催化剂含有一个未被占据的顶端位，用于亲电试剂和不依赖于刘易斯酸中心的萘氧化物的潜在配位。这些特征允许刘易斯酸性和布朗斯台德碱性位点的独立改变。这些独特的配合物已被证明可以催化丙二酸二苄酯和环己烯酮的Michael反应，具有良好的选择性（高达90%ee）和中等的产率（高达79%产率）。这些催化剂在其它烯酮和丙二酸酯之间的迈克尔反应中也是有效的。动力学数据表明，在Ni.Cs-BINOL-salen催化剂上，该反应为一级反应。进一步的实验探索了催化剂的各个刘易斯酸和布朗斯台德碱组分的反应性，并确定这两个部分对于不对称催化是必不可少的。总而言之，数据支持双功能活化途径，其中Ni.Cs-BINOL-salen的顶端Ni位点活化烯酮，并且萘氧化物碱活化丙二酸酯。
Salen metal complexes incorporating two chiral BINOL moieties have been synthesized and characterized by X-ray crystallography. The X-ray structures show that this new class of Ni-BINOL-salen catalysts contains an unoccupied apical site for potential coordination of an electrophile and naphthoxides that are independent from the Lewis acid center. These characteristics allow independent alteration of the Lewis acidic and Bronsted basic sites. These unique complexes have been shown to catalyze the Michael reaction of dibenzyl malonate and cyclohexenone with good selectivity (up to 90% ee) and moderate yield (up to 79% yield). These catalysts are also effective in the Michael reaction between other enones and malonates. Kinetic data show that the reaction is first order in the Ni.Cs-BINOL-salen catalyst. Further experiments probed the reactivity of the individual Lewis acid and Bronsted base components of the catalyst and established that both moieties are essential for asymmetric catalysis. All told, the data support a bifunctional activation pathway in which the apical Ni site of the Ni.Cs-BINOL-salen activates the enone and the naphthoxide base activates the malonate.