低价铁配合物催化C-C多重键硅氢化反应机理的理论研究

The hydrosilylation of alkene or alkyne catalyzed by transition-metal complexes is one of the most widely applied technologies for the selective generation of versatile silicon-containing products. The application of iron-based catalysts in the field of homogeneous catalysis has attracted considerable interest during the past decade. Because iron complexes own many advantages such as efficient catalytic activity, low price, environment friendly, etc. Combing the merits of iron chemistry and hydrosiliylation of alkene or alkyne, the significance of ion-catalyzed C-C multiplied bond hydrosilylation has been increasing emerging..Density functional theory (DFT) will be carried out to study the different mechanistic possibilities for the hydrosilylation of terminal alkene or alkynes catalyzed by iron carbonyl complexes, iron bis(dinitrogen) complex with a pyridinediimine ligand, iron complexes bearing bidentate cyclopentadienyl- functionalized N-heterocyclic carbine ligands. The competition of the potential side reactions will be examined. The catalyst activity and product selectivity will be proposed and analyzed in association with the following factors: combination of catalyst center and ligand, electronic and steric properties of ligands, important reaction conditions, and solvent effect. Our calculations will provide not only the structures of possible intermediates and transition states but also reveal the origination of the product chemo-, regio-, and enantio-selectivities. The rate-determining step with respect to the corresponding reaction system will be predicted on the basis of the detailed kinetics and energetics. This project will advance the understanding of the complexity of the detailed mechanisms of Fe-catalyzed alkene or alkyne hydrosilylations, and can afford valuable insights on the design and preparation of newly efficient iron-based catalysts and the effective control over reaction conditions.

以烯烃或炔烃为原料，经硅氢化反应选择性的合成高附加值产品具有广阔的应用前景。低价铁配合物由于其优良的催化性能、低廉的价格和环境友好等特点，近十多年在均相催化领域的应用价值日益凸现。本项目拟采用基于密度泛函理论（DFT）的第一性原理，对羰基铁配合物、双亚胺吡啶铁络合物、卡宾铁配合物催化烯烃或炔烃硅氢化反应进行理论计算研究，考察可能存在副反应的竞争性，系统分析催化剂金属中心与配体组合效应、配体电子效应和立体效应、重要反应条件以及溶剂效应对反应活性和产物选择性的影响，探寻反应过程所涉及的关键中间体和过渡态结构，获得基元步骤的动力学、热力学参数，阐明反应的速控步，揭示产物化学选择性和区域选择性的来源。该研究不仅可以为深入理解铁基催化烯烃/炔烃硅氢化反应机理提供理论依据，而且有望为新型高效廉价铁基配合物的设计合成和反应条件的有效调控提供有益思路。

以烯烃或炔烃为原料，经硅氢化反应选择性的合成高附加值产品具有广阔的应用前景。近年来凸现于均相催化领域的催化性能优良的、廉价的和环境友好的低价铁配合物的应用备受关注。本项目采用密度泛函理论（DFT），对几种低价铁催化的烯烃硅氢化反应和副反应进行了研究。结论如下：(1)反应底物HSiR3和烯烃与Fe(CO)4的配位能力相差不大，是造成Fe(CO)5催化反应化学选择性低的原因之一，即乙烯的去氢硅烷化与乙烯的硅氢化存在竞争。在计量反应中，乙烯硅氢化的催化循环（CH机理）略占优势。产物的选择性受乙烯插入Fe–Si键的过渡态和乙烯金属氢化物的异构化所控制。(2)反应底物HSiR3或H2与(MePDI)Fe的配位能力远超出烯烃，因而烯烃不会发生异构化。此类配合物在催化烯烃硅氢化时遵循CH机理，包括硅烷的配位活化，烯烃配位和氢化和Si–C还原消除。速控步与烯烃的配位和Si–C还原消除有关。(3)对Fe(CO)x(PR3)y的异构体、成键性质和稳定性等进行了研究。NBO证实，PR3具有强的σ-供体和弱的π-受体性质，中心Fe的电子密度增加，使得Fe与CO的反馈π键稍微增强。Fe–C键的键级变化次序按照R = Cy > Ph > Me > H > OPh > F的顺序减小，取代基R电负性越大，P的给电子性质越差，中心Fe的电子密度增加越少，Fe与CO的反馈π键增大的程度越小。第一膦配体解离能都低于Fe(CO)5的第一羰基解离能（PMe3除外），这表明膦配体修饰羰基铁化合物更有利于空配位点的产生。(4)真正的活性催化体16电子硅基铁配合物CpFe(CO)SiMe3是CpFe(CO)2Me经由乙醛解离路径获得的。由CpFe(CO)SiMe3引发的整个催化循环涉及：(i)1,3-二乙烯基二硅氧烷（1,3DVS）的配位与C=C双键插入Fe–Si键；(ii)由于SiMe3中甲基的立体排斥作用较强，中间体C经历C1–C2键旋转异构化得到抓氢化合物C1，之后原乙烯基端位氢迁移生成硅乙烯基铁氢化物F1；(iii) F1经异构化得到的乙烯基-铁氢化物G1发生C–H还原消除；(iv)氢硅烷的配位和硅乙基的加氢。本项目的完成揭示了低价铁催化的烯烃硅氢化的反应机理，有望为新型高效铁基配合物的设计合成提供有益思路。