Synthetic and Structural Insights into the Zincation of Toluene: Direct Synergic Ring Metallation versus Indirect Nonsynergic Lateral Metallation
Synthetic and Structural Insights into the Zincation of Toluene: Direct Synergic Ring Metallation versus Indirect Nonsynergic Lateral Metallation
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DOI：
10.1002/chem.200801928
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发表时间：
2009-01-01
影响因子：
4.3
通讯作者：
Mulvey, Robert E.
中科院分区：
文献类型：
--
作者：
Armstrong, David R.;Garcia-Alvarez, Joaquin;Mulvey, Robert E.
甲苯通过与杂配锌酸钠 [(tmeda)Na(tBu)-(tmp)Zn(tBu)] (1) 反应直接锌化，得到 [(tmeda)Na(C,H,Me)(tmp)Zn(tBu)] (2) 间位和对位区域异构体的统计混合物 (TMEDA = N,N,N',N'-四甲基乙二胺，TMP = 2,2,6,6-四甲基哌啶）。有趣的是，混合金属碱并未触及甲苯的甲基。两种区域异构体的晶体结构均已通过 X 射线晶体学阐明，揭示了一个共同的基序，其中锌与甲苯环位于同一平面，并与经历去质子化的碳牢固结合，形成共价 a 键；而钠采用垂直排列，与芳香环π键合。 1 与甲苯反应的 DFT 研究表明，在四种可能的区域异构体中，实验观察到的间位和对位异构体是热力学上最优选的产物，这在很大程度上归因于锌和钠的联合（协同）效应以及每种金属与甲苯基阴离子结合的不同方式。相比之下，更直接的苄基锌酸盐[(tmeda)(2)Na(CH2Ph)Zn(tBu)(2)](3)是通过间接途径获得的，其中甲苯首先被单金属丁基钠横向金属化，得到苄基钠，然后通过与tBu(2)Zn共络合形成混合金属化合物。锌酸盐 3 已通过固态 X 射线晶体学和氘化 THF 溶液中的 NMR 光谱进行了表征。
Toluene has been directly zincated by reaction with the heteroleptic sodium zincate [(tmeda)Na(tBu)-(tmp)Zn(tBu)] (1) to afford a statistical mixture of the meta and para regioisomers of [(tmeda)Na(C,H,Me)(tmp)Zn(tBu)] (2) (TMEDA = N,N,N',N'-tetramethylethylenediamine, TMP = 2,2,6,6-tetramethylpiperidide). Interestingly, the methyl group of toluene has been left untouched by the mixed-metal base. The crystal structures of both regioisomers have been elucidated by using X-ray crystallography, which revealed a common motif, in which zinc lies in the same plane as the tolyl ring and binds strongly to the carbon that has experienced the deprotonation, leading to a covalent a bond; whereas sodium adopts a perpendicular disposition, pi-engaging with the aromatic ring. DFT studies of the reaction of 1 with toluene showed that of the four possible regioisomers, the experimentally observed meta and para ones are the most thermodynamically preferred products due to a large extent to the combined (synergic) effect of the zinc and sodium and the different way in which each metal binds to the tolyl anion. In contrast, the more straightforward benzyl-based zincate [(tmeda)(2)Na(CH2Ph)Zn(tBu)(2)] (3) is obtained through an indirect route, in which toluene is first laterally metallated by monometallic butylsodium to afford benzylsodium, which then forms a mixed-metal compound by co-complexation with tBu(2)Zn. Zincate 3 has been characterised by X-ray crystallography in the solid state and by NMR spectroscopy in deuterated THF solution.