镁-三苯胺基MOF的制备及光/Lewis酸协同催化

Preparation of magnesium-triphenylamine based MOF for synergistic Lewis acid and photoredox catalysis

摘要:

利用水热法将具有Lewis酸性的Mg2+ 和光敏性的三苯胺三羧酸（H3TCA）自组装，构筑了金属有机框架（metal-organic framework; MOF）Mg-TCA，并通过SC-XRD表征了其晶体结构。UV-vis、FL、CV等测试表明Mg-TCA在可见光区（> 400 nm）具有良好的吸收，其激发态氧化还原电位为-1.95 V (vs. SCE)。以苯乙烯类化合物（0.2 mmol）为底物，NHPI活性酯（0.3 mmol）为自由基前体，Mg-TCA（0.01 mmol）为催化剂，DMSO（2 mL）为溶剂和氧化剂，氮气保护，在405nm的LED下照射24 h，反应以30%~82%的产率生成相应的α-烷基苯乙酮。催化剂Mg-TCA可以重复使用3次并且仍保持活性和晶态结构。机理研究表明在反应过程中发生了光/Lewis酸协同催化，Mg-TCA中具有Lewis酸性的镁节点对NHPI活性酯的吸附作用拉近了其与光催化中心三苯胺的距离，从而提升了催化反应的效率。

Abstract:

Self-assembly between Lewis acidic Mg2+ and photoredox tricarboxytriphenyl amine (H3TCA) constructs a metal organic framework Mg-TCA. SC-XRD was used to determine the crystal structure. UV-vis spectrum indicates that Mg-TCA has a good absorption ability in visible light region. CV,UV-vis and FL measurements indicate that the redox potential of the photoexcited Mg-TCA is -1.95 V (vs. SCE). Mg-TCA can effectively allow access to a wide range of α-alkyl-acetophenones (30%~82%) under the synergistic Lewis acid and photoredox catalysis, and the reaction conditions is shown as below: styrene substrate (0.2 mmol), NHPI ester (0.3 mmol), Mg-TCA (0.01 mmol), DMSO (2 mL), irradiated by 405 nm LED for 24 h at N2 atmosphere. The catalyst can be reused for three times without deactivation, and its structure remains intact before and after use. Mechanism studies indicate a synergistic Lewis acid and photoredox catalysis process within this transformation, the Lewis acidic nodes of Mg-TCA can bind and absorb NHPI ester, putting the NHPI ester approximate to the photoredox catalytic center within Mg-TCA, thus improving the catalytic efficiency.