Solvent-Separated and Contact Ion Pairs of Parent Lithium Trimethyl Zincate
Solvent-Separated and Contact Ion Pairs of Parent Lithium Trimethyl Zincate
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DOI：
10.1002/anie.200901587
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发表时间：
2009-01-01
影响因子：
16.6
通讯作者：
Stalke, D.
中科院分区：
文献类型：
--
作者：
Merkel, S.;Stern, D.;Stalke, D.
双金属试剂是由一个碱金属离子、第二个金属原子（Zn、Al或Mg）和可变配体组成的，由于它们的反应模式容易优于简单的单金属，因此在过去几年中受到了广泛的关注特别是锌酸盐配合物，尽管化学家们知道它已有150多年的历史，但最近才发现[2]可以在普通有机锂和有机镁化合物都无法达到的位置上金属酸取代芳香底物。在他们的开创性工作中，Mulvey和同事将元去质子化引入芳香化学，补充了Snieckus和同事建立的定向邻位金属化（DoM）他们可以用氨基锌酸盐[(tmeda) Na-(μ-tBu)(μ-tmp) ZntBu)][4]和甲苯[(tmeda) Na-(μ-Bu)(μ-tmp) Mg (tmp)][5]（tmeda=四甲基乙二胺，tmp=四甲基哌酸酯）金属化N， N-二甲基苯胺以前难以接近的间位。另一个方面是许多取代芳烃的顺利锌化，而传统上使用的有机锂化合物由于与许多官能团不相容而无法做到这一点这些优势的盐配合物比他们的单金属同系物已被认可为协同效应。在1917年关于碱金属有机物的里程碑式论文中，施伦克和霍尔茨详细阐述了二乙基锌与锂或钠的反应只产生锌和一种碱金属乙基锌化合物；因此，嬗变不会发生。为了促进金属转化，他们使用了双有机汞化合物。现在有许多涉及R2Hg/R ' li体系的转金属反应的例子，但R2Zn/R ' li体系通常产生一般成分为Li2ZnR2R ‘ 2或li2nr2r ’的锌酸锂。[9-11]也报道了有机锂化合物与二甲基锌发生意外的转金属反应生成二有机锌配合物
Bimetallic reagents, which are composed of one alkali metal ion, a second metal atom (Zn, Al, or Mg), and variable ligands have gained much attention over the last few years since they show a reactivity pattern that easily outperforms simple monometallic species.[1] Especially zincate complexes, although known to chemists for more than 150years,[2] recently have been discovered to metalate substituted aromatic substrates at positions that can be reached neither by common organolithium nor by organomagnesium compounds alone. In their pioneering work, Mulvey and co-workers introduced the meta deprotonation into aromatic chemistry, complementing the established directed ortho metalation (DoM) by Snieckus and co-workers.[3] They were able to metalate the previously inaccessible meta position of N, N-dimethylaniline employing the amido zincate [(tmeda) Na-(μ-tBu)(μ-tmp) ZntBu)][4] and of toluene using [(tmeda) Na-(μ-Bu)(μ-tmp) Mg (tmp)][5](tmeda= tetramethylethylenediamine; tmp= tetramethylpiperidide). Another aspect is the smooth zincation of many substituted aromatics for which the traditionally used organolithium compounds fail because of their incompatibility with many functional groups.[6] These advantages of ate complexes over their monometallic congeners have been accredited to synergistic effects. In their milestone paper on alkali-metal organics in 1917,[7] Schlenk and Holtz elaborated that the reaction of diethylzinc and lithium or sodium yields only zinc and an alkali-metal ethylzinc compound; hence, transmetalation does not occur. To favor transmetalation, they employed diorganomercury compounds instead. Nowadays there are many examples of transmetalation reactions involving the R2Hg/R’Li system,[8] but the R2Zn/R’Li system normally yields lithium zincates of the general composition Li2ZnR2R’2 or LiZnR2R’.[9–11] An unexpected transmetalation reaction of an organolithium compound and dimethyl zinc to give a diorganozinc complex was reported as well.[12]