Zhao Liang, Cai Wei, Ji Guanfeng, Wei Jianwei, Du Zenggang, He Cheng, Duan Chunying
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, P. R. China.
Inorg Chem. 2022 Jun 27;61(25):9493-9503. doi: 10.1021/acs.inorgchem.2c00441. Epub 2022 Jun 13.
Metal-organic frameworks (MOFs) have gained attention as multifunctional catalytic platforms, allowing us to gain important insights into synergistically activating both C-H bonds and oxygen for improving oxidation. Herein, by ingenious incorporation of anthraquinone, we report an anthraquinone-based MOF as a bifunctional heterogeneous photocatalytic platform to simultaneously activate inert C(sp)-H bonds and oxygen for C-H bond oxidation. Making use of the rigid framework with the fixation and isolation effect, both a great chemical stability and bifunctional synergistic photocatalytic effects were obtained through the immobilization of anthraquinone into a MOF. Importantly, while decorating two carboxyl groups on anthraquinone, the carbonyl groups of anthraquinone photosensitizers were not involved in coordinating the self-assembly and orderly arranged on the wall of channels that were constructed through a π-π interaction between the anthraquinone moieties in the adjacent layers, which was beneficial to form and stabilize the excited-state radical intermediates in the molecule-fenced channels, and the close proximity between the catalytic sites and the substrates to abstract a hydrogen atom from the substrate through the hydrogen atom transfer process aimed at activating the inertness of C-H bonds. Moreover, high-density-distributed anthraquinone dyes in the confined channels would activate oxygen to form singlet oxygen (O) through an energy transfer pathway, further promoting inert C(sp)-H bond oxidation efficiency. Under visible light irradiation, this anthraquinone-based MOF was successfully applied to explore activation and oxidation of a series of substrates containing benzylic C(sp)-H bonds in the presence of air or oxygen to produce the corresponding carbonyl products. This bifunctional photocatalytic platform based on a heterogeneous MOF provides an available catalytic avenue to develop a scalable and sustainable synthetic strategy using green and sustainable oxygen as the potent oxidant.
金属有机框架材料（MOFs）作为多功能催化平台已受到关注，这使我们能够深入了解协同活化碳氢键和氧以改善氧化反应的重要见解。在此，通过巧妙地引入蒽醌，我们报道了一种基于蒽醌的MOF作为双功能多相光催化平台，用于同时活化惰性碳（sp）-氢键和氧以实现碳氢键氧化。利用具有固定和隔离作用的刚性框架，通过将蒽醌固定到MOF中，获得了良好的化学稳定性和双功能协同光催化效果。重要的是，在蒽醌上修饰两个羧基时，蒽醌光敏剂的羰基不参与自组装配位，而是有序排列在通过相邻层中蒽醌部分之间的π-π相互作用构建的通道壁上，这有利于在分子围栏通道中形成和稳定激发态自由基中间体，并且催化位点与底物之间的紧密接近有利于通过氢原子转移过程从底物中提取氢原子，从而激活碳氢键的惰性。此外，受限通道中高密度分布的蒽醌染料将通过能量转移途径活化氧以形成单线态氧（O），进一步提高惰性碳（sp）-氢键的氧化效率。在可见光照射下，这种基于蒽醌的MOF成功地应用于在空气或氧气存在下探索一系列含有苄基碳（sp）-氢键的底物的活化和氧化，以生成相应的羰基产物。这种基于多相MOF的双功能光催化平台提供了一条可行的催化途径，以开发一种使用绿色可持续氧作为有效氧化剂的可扩展且可持续的合成策略。
