Chemical bonding and the equilibrium composition of Grignard reagents in ethereal solutions.
Chemical bonding and the equilibrium composition of Grignard reagents in ethereal solutions.
复制标题
醚溶液中格氏试剂的化学键合和平衡组成。
DOI：
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发表时间：
2011
影响因子：
2.9
通讯作者：
André G H Barbosa
中科院分区：
文献类型：
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作者：
André M. Henriques;André G H Barbosa
一个彻底的电子结构和热力学方面的格氏试剂及其相关的平衡组成在空灵溶液进行了分析。考虑到含氟、氯和溴的甲基卤化镁，我们研究了中性、带电和自由基在溶液中的化学平衡。所考虑的醚溶剂四氢呋喃（THF）和乙醚（Et(2)O）采用极化连续体模型（PCM）和簇中Mg原子的显式配位建模。用广义价键（GVB）波函数详细分析了构成格氏试剂的物质之间的化学键。用DFT/M06泛函和GVB波函数计算了平衡常数，得到了相似的结果。根据我们的计算和现有的动力学和电化学证据，R（•），R(-),（•）MgX和RMgX(2)（-）在平衡中必须以低浓度存在。我们得出结论，根据卤素的不同，在每种情况下必须遵循不同的途径来产生相关的平衡物质。氯化物和溴化物最好遵循“基自由基”的途径，氟化物必须遵循“基碳”的途径。这些不同的机制与现有的实验结果进行了对比，并证明了与现有的格氏试剂平衡热力学数据是一致的。
A thorough analysis of the electronic structure and thermodynamic aspects of Grignard reagents and its associated equilibrium composition in ethereal solutions is performed. Considering methylmagnesium halides containing fluorine, chlorine, and bromine, we studied the neutral, charged, and radical species associated with their chemical equilibrium in solution. The ethereal solvents considered, tetrahydrofuran (THF) and ethyl ether (Et(2)O), were modeled using the polarizable continuum model (PCM) and also by explicit coordination to the Mg atoms in a cluster. The chemical bonding of the species that constitute the Grignard reagent is analyzed in detail with generalized valence bond (GVB) wave functions. Equilibrium constants were calculated with the DFT/M06 functional and GVB wave functions, yielding similar results. According to our calculations and existing kinetic and electrochemical evidence, the species R(•), R(-), (•)MgX, and RMgX(2)(-) must be present in low concentration in the equilibrium. We conclude that depending on the halogen, a different route must be followed to produce the relevant equilibrium species in each case. Chloride and bromide must preferably follow a "radical-based" pathway, and fluoride must follow a "carbanionic-based" pathway. These different mechanisms are contrasted against the available experimental results and are proven to be consistent with the existing thermodynamic data on the Grignard reagent equilibria.