Heavier Alkaline Earth Catalysts for the Intermolecular Hydroamination of Vinylarenes, Dienes, and Alkynes
Heavier Alkaline Earth Catalysts for the Intermolecular Hydroamination of Vinylarenes, Dienes, and Alkynes
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DOI：
10.1021/ja209135t
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发表时间：
2012-02-01
影响因子：
15
通讯作者：
Procopiou, Panayiotis A.
中科院分区：
文献类型：
--
作者：
Brinkmann, Christine;Barrett, Anthony G. M.;Procopiou, Panayiotis A.
较重的第 2 族配合物 [M{N(SiMe3)(2)}(2)](2) (1, M = Ca; 2, M = Sr) 和 [M{CH(SiMe3)(2)}(2)(THF)(2)] (3, M = Ca; 4, M = Sr) 被证明是乙烯基芳烃和二烯分子间氢胺化的有效预催化剂。 条件温和。初步研究表明，酰胺预催化剂 1 和 2 虽然因转氨基行为的倾向而在绝对活性方面受到影响，但对聚合/低聚副反应具有更高的稳定性。在每种情况下，锶物质 2 和 4 的性能均优于其钙同系物。哌啶与对位取代的苯乙烯的反应表明催化循环中决定速率的烯烃插入，而仲环胺的添加难易程度被发现取决于环的大小，并被认为是胺亲核性变化的结果。共轭二烯的氢胺化，通过 eta(3)-烯丙基中间体产生异构产物，并通过立体电子学的考虑解释了它们的相对分布。发现进行内部炔烃加氢胺化的能力是显着依赖的。根据炔烃取代基的身份，而使用末端炔烃的反应导致不溶性且非反应性的第2族乙炔化物沉淀。 [Sr{N(SiMe3)(2)}(2)](2) 催化的苯乙烯与哌啶氢胺化反应的速率定律在[胺]和[烯烃]中为一阶速率定律，在[催化剂]中为二阶速率定律，而大的动力学同位素效应和第2族元素依赖的Delta S双匕首值暗示了胺辅助限速烯烃的形成 插入过渡态，其中与较大的锶中心的使用相关的相当大的熵优势。
The heavier group 2 complexes [M{N(SiMe3)(2)}(2)](2) (1, M = Ca; 2, M = Sr) and [M{CH(SiMe3)(2)}(2)(THF)(2)] (3, M = Ca; 4, M = Sr) are shown to be effective precatalysts for the intermolecular hydroamination of vinyl arenes and dienes under mild conditions. Initial studies revealed that the amide precatalysts, 1 and 2, while compromised in terms of absolute activity by a tendency toward transaminative behavior, offer greater stability toward polymerization/oligomerization side reactions. In every case the strontium species, 2 and 4, were found to outperform their calcium congeners. Reactions of piperidine with para-substituted styrenes are indicative of rate-determining alkene insertion in the catalytic cycle while the ease of addition of secondary cyclic amines was found to be dependent on ring size and reasoned to be a consequence of varying amine nucleophilicity. Hydroamination of conjugated dienes, yielded isomeric products via eta(3)-allyl intermediates and their relative distributions were explained through stereoelectronic considerations. The ability to carry out the hydroamination of internal alkynes was found to be dramatically dependent. upon the identity of the alkyne substituents while reactions employing terminal alkynes resulted in the precipitation of insoluble and unreactive group 2 acetylides. The rate law for styrene hydroamination with piperidine catalyzed by [Sr{N(SiMe3)(2)}(2)](2) was deduced to be first order in [amine] and [alkene] and second order in [catalyst], while large kinetic isotope effects and group 2 element-dependent Delta S double dagger values implicated the formation of an amine-assisted rate-determining alkene insertion transition state in which there is a considerable entropic advantage associated with use of the larger strontium center.