Borylated Phenol and Phenoxyl Radical: Synthesis, Electrochemistry, and Magnetic Property
Date Issued
2014
Date
2014
Author(s)
Feng, Po-Yeng
Abstract
Free radicals that are exclusively composed of non-metal elements are relatively unstable, and generally require specific electronic and steric stabilization effects to realize the structural characterization of these open-shelled species. To date, substitution of organic free radicals with diarylboryl group has only been reported for few times. Taking into account the sigma-donating ability governed by the electropositive nature of boron, the boryl substituent should help in stabilizing the electron deficient phenoxyl radical. Furthermore, the empty p-orbital at boron could delocalize the un-paired electron and lead to stable free radicals. To evaluate the idea, we have prepared the dimesityl boryl substituted phenoxyl radical, and to investigate its structural changes under redox events. Interestingly, we have also discovered an electron reduction triggered sequential electron and hydrogen atom transfer process, which leads to transformation from a hydroxyphenyl-substituted borane to a hydridoborate phenoxide dianion. The neutral borylated phenoxyl radical could be further reduced with cobaltocene to the corresponding benzoquinone borataalkene derivative. ESR spectroscopic measurement of the free radical reveals a hyperfine-coupling constant of 3.424 G and 1.142 G to the 11B (I = 3/2) and 10B (I = 3) nuclei, respectively. This result indicated that the boryl substituent indeed stabilizes the open-shelled species through delocalization of the spin density on the phenol ring.
Subjects
酚自由基
硼烷
電子轉移
氫原子轉移
還原
Type
thesis
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