DFT studies on the borylation of α,β-unsaturated carbonyl compounds catalyzed by phosphine copper(I) boryl complexes and observations on the interconversions between O- and C-bound enolates of Cu, B, and Si
DFT studies on the borylation of α,β-unsaturated carbonyl compounds catalyzed by phosphine copper(I) boryl complexes and observations on the interconversions between O- and C-bound enolates of Cu, B, and Si
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DOI：
10.1021/om8006294
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发表时间：
2008-09-08
期刊：
影响因子：
2.8
通讯作者：
Marder, Todd B.
中科院分区：
文献类型：
--
作者：
Dang, Li;Lin, Zhenyang;Marder, Todd B.
用密度泛函理论方法研究了膦铜(I)硼配合物催化α，β-不饱和羰基化合物、丙烯醛和丙烯酸甲酯的硼化反应机理。结果表明，催化的硼化反应是通过C=C插入到Cu-B中，生成与β-硼烷基碳键合的铜(I)烯酸酯中间体。在丙烯醛的硼化反应中，C键的铜(I)烯酸酯经酮基烯醇异构化得到O键的烯醇中间体，然后与二硼试剂进行a键的易位反应。在甲基丙烯酸酯的硼化反应中，由于酯基的惰性，不会发生酮基到烯醇的异构化。醇解或水解是必需的，以有效地将C-键的铜(I)烯醇化中间体转化为能够容易地与二硼试剂进行a-键歧化的硼化产物和铜(I)醇盐。丙烯醛和丙烯酸甲酯不同的硼化反应机理与两类不同底物反应所涉及的C-和O-烯酸酯中间体的相对热力学和动力学稳定性密切相关。比较了乙烯、甲醛、丙烯醛(2-丙二醛，CH2=CH-CHO)和丙烯酸甲酯(CH2=CH-CO2Me)插入铜-B键的反应。结果发现，插入势垒与计算的四种底物的Lumo轨道能有很好的相关性，支持插入主要涉及配位的不饱和底物分子上的Cu-B a键的亲核攻击的观点。虽然甲醛在插入反应中比乙烯更活跃，但在α、β-不饱和醛和酯中，C=C键的反应活性大于C=O键。此外，还研究了铜、硼和硅的O-键和C-键的烯醇酸盐之间相互转化的热力学和动力学。
The detailed mechanisms for the borylation of alpha,beta-unsaturated carbonyl compounds, acrolein and methylacrylate, catalyzed by phosphine copper(I) boryl complexes were studied with the aid of density functional theory calculations. The results show that the catalyzed borylation occurs through C=C insertion into Cu-B to give a beta-borylalkyl C-bound Cu(I) enolate intermediate. In the borylation of acrolein, the C-bound Cu(I) enolate undergoes a keto-to-enol isomerization to give an O-bound enolate intermediate followed by a a-bond metathesis with a diboron reagent. In the borylation of methylacrylate, a keto-to-enol isomerization does not occur due to the inertness of the ester group. Alcoholysis or hydrolysis is necessary to convert the C-bound Cu(I) enolate intermediate efficiently to the borylation product and Cu(I) alkoxide that can easily undergo a-bond metathesis with a diboron reagent. The different borylation reaction mechanisms of acrolein and methylacrylate are closely related to the relative thermodynamic and kinetic stability of the C- and O-enolate intermediates involved in the reactions of the two different classes of substrates. The insertion reactions of ethene, formaldehyde, acrolein (2-propenal, CH2=CH-CHO), and methylacrylate (CH2=CH-CO2Me) into a Cu-B bond were compared. It was found that the insertion barriers correlate very well with the orbital energies of the LUMOs calculated for the four substrates, supporting the notion that the insertion mainly involves a nucleophilic attack of the Cu-B a bond at the coordinated unsaturated substrate molecule. Although formaldehyde is more active than ethene in the insertion reaction, the reactivity of the C=C bond is greater than that of the C=O bond in alpha,beta-unsaturated aldehyde and ester. In addition, the thermodynamics and kinetics of interconversions between O- and C-bound enolates of Cu, B, and Si have been investigated.