Thompson Benjamin J, Kumar Anshu, Huxter Vanessa M
Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, USA.
Department of Optical Sciences, University of Arizona, Tucson, Arizona 85721, USA.
Phys Chem Chem Phys. 2024 Jul 24;26(29):19900-19907. doi: 10.1039/d4cp02026j.
Hydroxylation reactions are important in biological processes and synthetic schemes. Many challenging hydroxylation reactions have been achieved using photoredox catalytic methods. For the oxidative hydroxylation of arylboronic acids, methylene blue has been used successfully as a photoredox catalyst to produce phenyl groups. Here we use broadband transient absorption spectroscopy to determine the mechanism of the photoredox catalytic reaction of methylene blue with phenylboronic acid in the presence of -diisopropylethylamine. Our results show that the reaction proceeds through the triplet state of methylene blue in the presence of oxygen, generating superoxide radical anions. In addition, we observe dimerization of the methylene blue at typical catalytic loadings. As these dimers do not participate in the reaction, increasing the concentration of methylene blue is potentially detrimental to the overall yield.
羟基化反应在生物过程和合成方案中都很重要。许多具有挑战性的羟基化反应已通过光氧化还原催化方法实现。对于芳基硼酸的氧化羟基化反应，亚甲蓝已成功用作光氧化还原催化剂以生成苯基。在此，我们使用宽带瞬态吸收光谱法来确定在二异丙基乙胺存在下亚甲蓝与苯硼酸的光氧化还原催化反应的机理。我们的结果表明，在有氧存在的情况下，反应通过亚甲蓝的三重态进行，生成超氧自由基阴离子。此外，我们观察到在典型的催化负载量下亚甲蓝会发生二聚化。由于这些二聚体不参与反应，增加亚甲蓝的浓度可能会对总产率产生不利影响。
