Elucidation of the Reaction Mechanisms of Hydrosilylations with Cationic Transition-Metal Catalysts

阳离子过渡金属催化剂氢化硅烷化反应机理的阐明

• 批准号: 427411484
• 负责人: Professor Dr. Martin Oestreich
• 金额: --
• 依托单位: Institut für Chemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/427411484?language=en
• 关键词: Elucidation; Reaction; Mechanisms; Hydrosilylations; Cationic

The mechanistic understanding of chemical reactions is a fundamental requirement for their further development. We have been engaged for quite a while in the experimental elucidation of the ionic hydrosilylation of carbonyl compounds catalyzed by main-group Lewis acids and transition-metal complexes, respectively. The key insight of our preliminary work is that those hydrosilylation reactions that are promoted by cationic transition-metal catalysts do not proceed by their postulated reaction mechanisms. Our laboratory showed for two prominent cases that the neutral transition-metal hydride formed as an intermediate during the catalysis is not sufficiently hydridic to reduce the silylcarboxonium ion. Another molecule of the hydrosilane is needed to activate that transition-metal hydride either by coordination or even oxidative addition of the Si‒H bond (two-silicon rather than one-silicon cycle). Hence, more than one equivalent of the hydrosilane is required to accelerate and drive these hydrosilylations to completion. The consequences of this finding are far-reaching as it means that reported mechanisms of related hydrosilylation reactions are also likely to require partial revision. Within this project, we verify the generality of our hypothesis by systematically looking into the mechanisms of two additional representative carbonyl hydrosilylations. We hope that a universally valid mechanistic picture will evolve from this.

对化学反应机理的理解是其进一步发展的基本要求。我们长期以来一直致力于主族路易斯酸和过渡金属络合物催化的羰基化合物的离子氢化硅烷化的实验阐明。我们前期工作的关键见解是，那些由阳离子过渡金属催化剂促进的氢化硅烷化反应并不按照其假设的反应机制进行。我们的实验室在两个突出案例中表明，在催化过程中作为中间体形成的中性过渡金属氢化物的氢性不足以还原甲硅烷基碳鎓离子。需要另一个氢硅烷分子通过配位甚至氧化加成 Si-H 键（双硅而不是单硅循环）来激活过渡金属氢化物。因此，需要超过一当量的氢硅烷来加速并驱动这些氢硅烷化反应完成。这一发现的影响是深远的，因为它意味着相关氢化硅烷化反应的报道机制也可能需要部分修改。在这个项目中，我们通过系统地研究另外两个代表性羰基氢化硅烷化的机制来验证我们假设的普遍性。我们希望由此发展出一个普遍有效的机制图景。