Expanding Mg-Zn hybrid chemistry: inorganic salt effects in addition reactions of organozinc reagents to trifluoroacetophenone and the implications for a synergistic lithium-magnesium-zinc activation.
Expanding Mg-Zn hybrid chemistry: inorganic salt effects in addition reactions of organozinc reagents to trifluoroacetophenone and the implications for a synergistic lithium-magnesium-zinc activation.
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DOI：
10.1002/chem.201100866
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发表时间：
2011-07
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通讯作者：
D. Armstrong;W. Clegg;Pablo García‐Álvarez;A. Kennedy;Matthew D. McCall;Luca Russo;Eva Hevia
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文献类型：
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作者：
D. Armstrong;W. Clegg;Pablo García‐Álvarez;A. Kennedy;Matthew D. McCall;Luca Russo;Eva Hevia
许多有机转化依赖于有机锂或格氏试剂与合适的锌前驱体通过盐复分解（交换）反应制成的有机锌化合物。通过结合x射线晶体学，核磁共振波谱学和DFT计算，本研究揭示了这个重要合成工具中涉及的有机金属物种的构成。通过研究等摩尔量的格氏试剂（RMgX）和ZnCl(2)在THF中的复分解反应，分离出了新的镁锌杂化合物[{(THF)(2)Mg(μ-Cl)(3)ZnR}(2)] (R=Et, tBu， nBu或o-OMe-C(6)H(4))，在混合镁锌化学中表现出前所未有的结构基序。此外，EtMgCl与ZnCl(2)反应的理论模型表明，混合金属化合物的形成比预期的同金属产物RZnCl和MgCl(2)的形成更有利。本研究还评估了杂化3对敏感酮三氟苯酮的烷基化能力，揭示了当LiCl作为添加剂引入时，反应的化学选择性显着增加。这一观察结果，结合最近在合成方面的相关突破，指出存在三边Li/Mg/Zn协同效应。
Numerous organic transformations rely on organozinc compounds made through salt-metathesis (exchange) reactions from organolithium or Grignard reagents with a suitable zinc precursor. By combining X-ray crystallography, NMR spectroscopy and DFT calculations, this study sheds new light on the constitution of the organometallic species involved in this important synthetic tool. Investigations into the metathesis reactions of equimolar amounts of Grignard reagents (RMgX) and ZnCl(2) in THF led to the isolation of novel magnesium-zinc hybrids, [{(thf)(2)Mg(μ-Cl)(3)ZnR}(2)] (R=Et, tBu, nBu or o-OMe-C(6)H(4)), which exhibit an unprecedented structural motif in mixed magnesium-zinc chemistry. Furthermore, theoretical modelling of the reaction of EtMgCl with ZnCl(2) reveals that formation of the mixed-metal compound is thermodynamically preferred to that of the expected homometallic products, RZnCl and MgCl(2). This study also assesses the alkylating ability of hybrid 3 towards the sensitive ketone trifluoroacetophenone, revealing a dramatic increase in the chemoselectivity of the reaction when LiCl is introduced as an additive. This observation, combined with recent related breakthroughs in synthesis, points towards the existence of a trilateral Li/Mg/Zn synergistic effect.