| Autor: |
Thompson BJ; Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, USA. vhuxter@arizona.edu.; Department of Optical Sciences, University of Arizona, Tucson, Arizona 85721, USA., Kumar A; Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, USA. vhuxter@arizona.edu.; Department of Physics, University of Arizona, Tucson, Arizona 85721, USA., Huxter VM; Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, USA. vhuxter@arizona.edu.; Department of Physics, University of Arizona, Tucson, Arizona 85721, USA. |
| Abstrakt: |
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 N,N -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. |
