金属氮杂环卡宾共价有机框架材料的构筑及其在二氧化碳催化氢化中的应用

In consideration of the lack of efficient catalysts and the unclear reaction mechanism of the hydrogenation carbon dioxide to methanol, this proposal mainly focused on the synthesis, characterization and application of novel N-heterocyclic carbene metal complexes (M-NHCs) as homogenous catalysts in the corresponding transformation based on our previous study. By using hydrogenation transformation of carbon dioxide as model reactions, the corrections between the skeletons and structures of M-NHCs, the corresponding steric and/or electronic effects and the catalytic efficiency, reaction conversion and selectivity would be fully explored, which helps us to explore the plausible hydrogenation mechanism and optimize the viable catalysts. Furthermore, in combination with the possible outcomes from the homogeneous catalytic study and correlation between catalyst structure and activity, a series of covalent organic frameworks (COFs) have been proposed via covalent assembly by linkers and the functional units derived from privileged homogenous NHC ligands, which could be function as robust, highly efficient and selective, and reusable solid molecular catalysts for the sustainable conversion of carbon dioxide to valuable platform molecules. In comparison to the plausible homogenous catalytic mechanism, the micro-nano effects including isolation effect, confinement effect, interface effect, cooperative effect, size effect and amplification effect would be fully investigated to realize straightforward, highly efficient and highly selective hydrogenation of carbon dioxide under the mild reaction conditions, which may further guide and extend their potential towards green, sustainable and energy chemistry with potential industrial applicability.

本项目主要针对目前二氧化碳催化氢化制备甲醇中高效催化剂缺失及机理不清等主要问题，基于我们课题组在氮杂环金属卡宾化合物制备、组装及其催化应用方面的前期工作，拟设计和开发一系列新型氮杂环金属卡宾均相催化剂，利用二氧化碳催化氢化反应，考察其骨架、结构、位阻及电子效应对催化效率、反应转化率及选择性的影响，达到优化催化剂结构、深入探究反应机理的目的。随后在总结均相催化剂构效关系的基础上，通过共价键组装策略，利用基于优势金属氮杂环卡宾基元砌块发展一系列用于二氧化碳绿色催化转化且稳定、高效、高选择性，可重复使用的COF型固体分子催化剂。结合均相催化机理着重研究这类新型固体晶态COF催化材料的孤立效应、限域效应、界面效应、协同效应、尺寸效应及放大效应，实现在温和条件下二氧化碳催化氢化转化，拓宽其在绿色催化和能源化学中的应用范围，从而提高实用性为其工业化奠定研究基础。

针对目前CO2催化氢化等高值转化中高效催化剂缺失及机理不清等主要问题，基于课题组前期在金属氮杂环卡宾化合物均相催化剂制备、组装及其催化应用方面的基础上，利用共价策略设计和开发了三类固体分子催化材料。首先，利用固定空间取向的二咪唑、三咪唑及四咪唑盐为前体，通过与不同金属共价配位组装的策略，高效构筑了一系列共价自负载固体分子催化材料，在此基础上进一步实现了磁性核壳结构自负载型复合固体催化材料；其次，基于优势的双氮杂环卡宾金属化合物，利用傅克反应，通过直接共价交联策略，实现了一系列超交联固体分子催化材料的可控制备和催化中心的精准构筑，并将其拓展至钳形催化剂体系；最后，利用三聚氯氰替代常规的交联剂，基于双氮杂环卡宾金属化合物，制备了一系列共价三嗪框架（CTF）催化材料。在利用电镜、衍射、核磁、红外、吸附等多种手段进行详细表征后，发现所有的固体材料中金属中心是原子级分在在催化剂基质中的，其配位环境与相应的均相金属有机分子催化剂完全一致，在CO2氢化、氢甲酰化、氢胺甲基化等高值转化反应中显示出极高的催化活性、反应选择性和重复使用性。在此基础上，结合催化机理着重研究导致共价固体分子催化材料催化性能提升的孤立效应、限域效应、界面效应、协同效应、放大效应及尺寸效应，在温和条件下实现了多类CO2高值转化，为其产业化转化奠定了基础。