Recent Advances in Photo-Induced Catalysis Mediated by <i>N</i>-Heterocyclic Carbene Metal Complexes

氮杂环卡宾(N-Heterocyclic Carbenes, NHCs)本身具有高度共轭的平面五圆环结构，在和金属中心配位后能够通过σ-π协同作用稳定金属中心的氧化态，在光激发下，NHC配体能够通过分子内的电荷转移，将能量高效地传递至金属中心，使金属中心产生稳定的激发态活性。这种特殊的光物理性质能够显著地降低催化反应的活化能，实现更加绿色的催化方式。配体的易修饰特点也有利于引入特征官能团对复杂光诱导催化体系中的副反应进程进行针对性限制，甚至突破经典催化反应条件的局限性。此外，光源参数波长和强度的精确可控性，让光诱导的催化反应在复杂药物合成、功能材料制备以及光催化降解等多个重要领域都具有巨大的潜在应用价值。本文介绍了一系列具有光催化活性的氮杂环卡宾金属络合物的合成，及其在光照条件下的催化应用及相关反应机理。N-heterocyclic carbenes (NHCs) intrinsically possess a highly delocalized planar pentacyclic framework. Subsequent to coordination with the metallic core, they can stabilize the oxidation state of the metal via σ-π cooperative interactions. Upon photo-activation, NHC ligands are capable of transferring energy expeditiously to the metallic core through intramolecular charge displacement, thereby endowing the metallic core with stable excited-state reactivity. This distinctive photophysical property can significantly reduce the activation energy of the catalytic reaction, enabling a more environmentally friendly catalytic approach. The amenability of ligands to modification also facilitates the introduction of characteristic functional groups to specifically restrict the side-reaction processes in complex photo-induced catalytic systems, and even overcome the limitations of classical catalytic reaction conditions. Moreover, the precise controllability of the wavelength and intensity of the light source parameters endows photo-induced catalytic reactions with great potential application value in multiple important fields such as complex drug synthesis, functional material preparation, and photocatalytic degradation. This paper presents the synthesis of a series of N-heterocyclic carbene metal complexes with photocatalytic activity, as well as their catalytic applications under illumination conditions and the relevant reaction mechanisms.