Exposing the hidden complexity of stoichiometric and catalytic metathesis reactions by elucidation of Mg-Zn hybrids
Exposing the hidden complexity of stoichiometric and catalytic metathesis reactions by elucidation of Mg-Zn hybrids
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DOI：
10.1073/pnas.0913307107
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发表时间：
2010-03-23
影响因子：
11.1
通讯作者：
McCall, Matthew D.
中科院分区：
文献类型：
--
作者：
Hevia, Eva;Chua, Jonathan Z.;McCall, Matthew D.
令人惊讶的是，研究ZnCl 2和（BuMgCl）-Bu-t之间看似简单的复分解反应，揭示了一种更复杂的化学反应，涉及混合的镁-锌化合物，可以被视为Mg-Zn杂化物。因此，等摩尔量的ZnCl 2和tBuMgCl的反应揭示了前所未有的混合Mg-Zn络合物[（THF）（4）Mg（μ-Cl）（2）Zn（Bu-t）（Cl）]（1）的形成，这是复分解的两种预期交换产物的共络合的结果。这种锌酸镁采用接触离子对结构，与Knochel的开创性“Turbo”Grignard试剂密切相关。此外，在该反应中鉴定的第二副产物是溶剂分离的混合镁-氯化锌络合物[{Mg（THF）（6）}（2+）{Zn 2Cl 6}（2-）]（3），其严重减少了可用于发生预期复分解反应的ZnCl 2的量。在另一个令人惊讶的结果中，当通过使用过量的3 M当量的格氏试剂进行反应时，（更接近合成化学家使用的催化条件），溶剂分离三烷基锌酸镁[{Mg 2Cl 3（THF）（6）}（+）{Zn（Bu-t）（3）}（-）]（4）的获得，可以被看作是一个模型的活性物种参与越来越重要的有机转化的格氏试剂催化氯化锌。此外，初步的反应性研究表明，配合物4可以用作用于直接Zn-I交换反应的有效的新试剂，其允许制备和结构鉴定三（芳基）锌酸镁[{Mg 2Cl 3（THF）（6）}（+）{Zn（p-Tol）（3）}（-）]（5），其代表在Zn-I交换反应中锌酸盐的完全3倍活化的第一个实例，进而可有效地用作根岸交叉偶联反应的前体。
Studying seemingly simple metathesis reactions between ZnCl2 and (BuMgCl)-Bu-t has, surprisingly, revealed a much more complex chemistry involving mixed magnesium-zinc compounds that could be regarded as Mg-Zn hybrids. Thus, the reaction of equimolar amounts of ZnCl2 and tBuMgCl reveals the formation of the unprecedented mixed Mg-Zn complex [(THF)(4)Mg(mu-Cl)(2)Zn(Bu-t)(Cl)] (1), as a result of the co-complexation of the two anticipated exchange products of the metathesis. This magnesium zincate adopts a contacted ion-pair structure, closely related to Knochel's pioneering "Turbo" Grignard reagents. Furthermore, a second coproduct identified in this reaction is the solvent-separated mixed magnesium-zinc chloride complex [{Mg(THF)(6)}(2+){Zn2Cl6}(2-)] (3) that critically diminishes the amount of ZnCl2 available for the intended metathesis reaction to take place. In another surprising result, when the reaction is carried out by using an excess of 3 M equivalents of the Grignard reagent (closer to the catalytic conditions employed by synthetic chemists), solvent-separated magnesium trialkyl zincate [{Mg2Cl3(THF)(6)}(+){Zn(Bu-t)(3)}(-)] (4) is obtained that can be viewed as a model for the active species involved in the increasingly important organic transformations of Grignard reagents catalysed by ZnCl2. Furthermore, preliminary reactivity studies reveal that complex 4 can be used as an effective new reagent for direct Zn-I exchange reactions that allow the preparation and structural identification of the magnesium tris(aryl) zincate [{Mg2Cl3(THF)(6)}(+){Zn(p-Tol)(3)}(-)] (5) that represents the first example of complete 3-fold activation of a zincate in a Zn-I exchange reaction which, in turn, can efficiently be used as a precursor for Negishi cross-coupling reactions.