基于“金属-金属/配体-金属电子转移”分子氧活化催化剂构筑及其仿生催化烯烃环氧化

The direct epoxidation of alkenes with molecular oxygen is of great significance, but the vigorous activation conditions of the oxygen molecules make the alkenes easy to form allyl cations, resulting in problems such as reduced selectivity. Recently, the redox-active ligands have attracted much attention in successfully mimicking the electronic regulation function of biological enzymes. Despite of their dramatic enhancement for the multi-electron transfer ability of metals and activation of molecular oxygen at room temperature, the molecular designs of the ligands were limited to "ligand-metal charge transfer", which brought about the difficulty to obtain the active metal-oxo species for epoxidation. Our preliminary research work showed that the conjugated macrocyclic of bimetallic hexaphyrins could gently activate molecular oxygen to achieve selective epoxidation of alkenes, but the activation mechanism of molecular oxygen, catalytic mechanism and product selective regulation mechanism were not clear.. In view of the scientific problems of bimetallic hexaphyrin catalytic system, this project intends to clarify the structure-activity relationship between “the electronic structure and dinuclear metal of catalysts” and “the performances of activation and transmission of oxygen molecules”. A series of bimetallic hexaphyrins were proposed to be first constructed, and then carefully investigated by means of in-situ characterization techniques such as electron paramagnetic resonance, combined with theoretical calculations. Based on them, the regulation mechanism of product selectivity would be further clarified. The project is expected to provide new ideas for the design of biomimetic catalysts with adjustable electronic properties, as well as to enrich and develop the biomimetic catalytic system.

分子氧为氧源的烯烃直接环氧化具有重要意义，但氧分子剧烈的活化条件使得烯烃易于形成烯丙基阳离子，导致选择性降低等问题。近年来，模仿生物酶电子调节功能的氧化还原活性配体在增强金属多电子转移能力，促进分子氧室温活化方面引起了广泛关注。但其设计思路局限于“配体-金属电荷转移作用”，调控电子性质的手段单一，难以获得烯烃环氧化所需的高价金属氧代物。我们的前期研究工作表明，大环共轭结构的双金属六元卟啉可以较温和地活化分子氧，实现烯烃的选择性环氧化，但分子氧活化机制、催化机理及产物选择性调控机制仍未明确。.针对双金属六元卟啉体系分子氧活化与传递机制等科学问题，本项目拟通过构建一系列双金属六元卟啉，借助电子顺磁共振等原位表征技术，结合理论计算研究，阐明催化剂的电子结构及双核金属在氧分子活化与传递等方面的构效关系，明确产物选择性的调控机制，为构建电子性质可调的仿酶催化剂提供新的思路，丰富并发展仿生催化理论。

分子氧为氧源的烃类直接氧化具有重要意义。通过模仿生物酶，本项目设计并构建了大环共轭结构的双金属六元卟啉，可以较温和地活化分子氧、氮氧自由基前体，进而实现ppm级别催化剂载量、温和条件下，环己烯、丁烷等轻烃的选择性氧化及氨基衍生化。.针对双金属六元卟啉体系底物活化与自由基传递机制等科学问题，本项目通过构建一系列双金属六元卟啉，借助电子顺磁共振等原位表征技术，结合理论计算研究，阐明催化剂的大环配体及双核金属在自由基活性中间体活化与传递过程中主客体协同诱导质子耦合电子转移这一关键机理，明确产物选择性的调控机制。此外，我们受到双核金属六元卟啉协同催化特点的启发，将其作为金属物种限域前驱体结合球磨法，尝试构建了双原子纳米酶，发现原子对间距调控可以大幅提升其逆水煤气反应催化性能，其中双原子Ni的活性约为单原子Ni的2倍、纳米粒子的31倍，CO选择性接近100%。以上发现为构建电子性质可调的仿酶催化剂（模拟酶、仿生纳米酶）构建提供新的思路，丰富并发展均相/多相体系的仿生催化理论。