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首页> 外文期刊>Chemistry: A European journal >Catalyzing aldehyde hydrosilylation with a molybdenum(VI) complex: A density functional theory study
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Catalyzing aldehyde hydrosilylation with a molybdenum(VI) complex: A density functional theory study

机译：钼（VI）配合物催化醛氢化硅烷化：密度泛函理论研究

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[MoCl2O2] catalyzes the hydrosilylation reaction of aldehydes and ketones, as well as the reduction of other related groups, in apparent contrast to its known behavior as an oxidation catalyst. In this work, the mechanism of this reaction is studied by means of density functional theory calculations using the B3LYP functional complemented by experimental data. We found that the most favorable pathway to the first step, the Si-H activation, is a [2+2] addition to the Mo=O bond, in agreement with previous and related work. The stable intermediate that results is a distorted-square-pyramidal hydride complex. In the following step, the aldehyde approaches this species and coordinates weakly through the oxygen atom. Two alternative pathways can be envisaged: the classical reduction, in which a hydrogen atom migrates to the carbon atom to form an alkoxide, which then proceeds to generate the final silyl ether, or a concerted mechanism involving migration of a hydrogen atom to a carbon atom and of a silyl group to an oxygen atom to generate the silyl ether weakly bound to the molybdenum atom. In this Mo-VI system, the gas-phase free energies of activation for both approaches are very similar, but if solvent effects are taken into account and HSiMe3 is used as a source of silicon, the classical mechanism is favored. Several unexpected results led us to search for still another route, namely a radical path. The energy involved in this and the classical pathway are similar, which suggests that hydrosilylation of aldehydes and ketones catalyzed by [MoCl2O2] in acetonitrile may follow a radical pathway, in agreement with experimental results.
机译：[MoCl 2 O 2]催化醛和酮的氢化硅烷化反应以及其他相关基团的还原，这与其作为氧化催化剂的已知行为明显相反。在这项工作中，通过使用B3LYP官能团和实验数据进行补充的密度泛函理论计算，研究了该反应的机理。我们发现，第一步的最有利途径是Si-H活化，与先前和相关工作一致，是Mo = O键的[2 + 2]加成。产生的稳定中间体是扭曲的方形金字塔形氢化物配合物。在接下来的步骤中，醛接近该物种并通过氧原子微弱地配位。可以设想两种替代途径：经典还原，其中氢原子迁移至碳原子以形成醇盐，然后醇盐继续生成最终的甲硅烷基醚;或协同机制涉及氢原子迁移至碳原子甲硅烷基与氧原子相连，产生弱结合于钼原子的甲硅烷基醚。在此Mo-VI系统中，两种方法的活化气相自由能都非常相似，但是如果考虑到溶剂效应，并且将HSiMe3用作硅源，则倾向于经典机理。几项出乎意料的结果使我们寻找了另一条路线，即一条根本路线。该途径和经典途径涉及的能量相似，这表明[MoCl2O2]在乙腈中催化的醛和酮的氢化硅烷化可能遵循自由基途径，与实验结果一致。

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