硅宾化合物的合成及其均相催化反应性能探究

Silylenes, low-valent organosilicon, are the analogues of carbenes. The silicon centre possesses II oxidation state, and has a lone pair of electrons with high s-character as well as an active empty 3p orbital, which shows amphiphilic feature. Silylenes can react with small molecules via oxidative addition. However, due to the relatively high HOMO-LUMO energy gap and the insufficient matching of valence-orbital with that of substrates, the reductive elimination process is hard to occur, compared with transition-metal catalysis. Owing to the lack of suitable ligand and functional group system, the catalytic reactivity of such species has not been well explored hitherto. In this project, we plan to design and synthesize a series of silylene complexes with different ligands and functional groups in the coordination sphere, to investigate their transition-metal-like catalytic reactivity in functionalized olefin polymerization and small molecule hydroboration, which are two representative aspects in transition-metal catalysis. The anticipated results will provide a reliable base in both theory and experiment for the development of organosilicon chemistry in homogeneous catalysis field.

低价态有机硅化合物硅宾，是碳卡宾的14族重元素类似物。其硅原子呈II价，具有高度s特征的孤对电子和活泼的空3p轨道，兼具Lewis碱和Lewis酸的两性特征。相比过渡金属的反应性，硅宾可以通过氧化加成反应活化小分子，但因其HOMO-LUMO能垒偏大且与底物价层轨道匹配性不足，还原消除反应难以发生。因缺乏合适的配体与官能团体系以及催化反应种类，该物种的催化反应化学长期未有开拓。本项目拟设计合成系列硅宾化合物，选择过渡金属均相催化中两种代表性反应：极性官能团烯烃聚合和不饱和小分子硼氢化反应，探究不同配体和官能团体系的硅宾化合物的类过渡金属催化反应性能。本研究将为有机硅化学在均相催化领域的发展提供理论和实验依据。

本项目设计合成系列硅宾化合物，通过选取合适官能团体系调控硅中心外围的空间和电子结构，采用实验与理论计算相结合的方法探究硅宾化合物催化极性官能团烯烃聚合以及不饱和小分子硼氢化的反应性能。主要研究了：1. 一种RSi-SiR脒基双硅宾化合物在Lewis酸存在下与极性官能团烯烃的反应，揭示了其催化底物聚合反应活性，并结合量化计算佐证了一种FLP催化机理以及负氢转移链终止机理；2. 一种NHC-氢硅宾化合物用于催化各种不饱和小分子底物如CO2、取代醛酮、取代吡啶等的硼氢化反应性，并与外方合作进行DFT催化机理研究揭示了低价态Si(II)H基团的类过渡金属催化反应性能，且作为非金属催化剂，体现了绿色化学理念；3. 深入研究了脒基硅宾及其类似物与炔类和咪唑环等不饱和小分子的反应特性，展示了丰富的产物结构，揭示了低价态硅宾化合物新的反应模式。