Visible Light-Promoted Additions of Potassium Organotrifluoroborates to Imines
Poster Number
40
College
College of Arts and Sciences
Department
Chemistry, Physics, Geology, & the Environment
Faculty Mentor
James M. Hanna Jr., Ph.D.
Abstract
Recently, the use of visible light combined with a suitable photocatalyst to promote key bond-forming steps in organic synthesis has emerged as a viable strategy to achieve a number of important synthetic transformations. Visible light passes through ordinary glass, and organic substrates do not typically absorb wavelengths in the visible range, providing a significant advantage of this method over traditional ultraviolet (UV) photochemistry. The photocatalyst involved is often a ruthenium or iridium polypyridyl complex, which absorbs light in the visible range to give a relatively long-lived excited state. This photo-excited catalyst then mediates the formation of radicals from organic substrates, through a series of single-electron-transfer (SET) events; the organic radicals thus generated engage in downstream reactions, leading to the final product(s). We have begun exploring this strategy as a means to effect formal additions of potassium organotrifluoroborates to imines. We have found that irradiation of an argon-sparged dichloromethane solution of potassium benzyltrifluoroborate, benzalaniline, and diphenylphosphate in the presence of Ir-dF(CF3)-dtb at room temperature using blue LEDs (450 nm) yielded the expected addition product in 76% isolated yield; only traces of homocoupling products could be detected. Control experiments established that catalyst and light are both required for reaction; the elimination of diphenylphosphate led to a slightly lower yield. Light/dark experiments seemed to favor a single-cycle mechanism rather than a radical-chain mechanism.
Previously Presented/Performed?
68th Southeastern Regional Meeting of the American Chemical Society (SERMACS), Columbia, South Carolina, October 2016
Grant Support?
Supported by a grant from the National Institutes of Health IDeA Networks for Biomedical Research Excellence (NIH-INBRE)
Start Date
21-4-2017 2:15 PM
Visible Light-Promoted Additions of Potassium Organotrifluoroborates to Imines
Richardson Ballroom
Recently, the use of visible light combined with a suitable photocatalyst to promote key bond-forming steps in organic synthesis has emerged as a viable strategy to achieve a number of important synthetic transformations. Visible light passes through ordinary glass, and organic substrates do not typically absorb wavelengths in the visible range, providing a significant advantage of this method over traditional ultraviolet (UV) photochemistry. The photocatalyst involved is often a ruthenium or iridium polypyridyl complex, which absorbs light in the visible range to give a relatively long-lived excited state. This photo-excited catalyst then mediates the formation of radicals from organic substrates, through a series of single-electron-transfer (SET) events; the organic radicals thus generated engage in downstream reactions, leading to the final product(s). We have begun exploring this strategy as a means to effect formal additions of potassium organotrifluoroborates to imines. We have found that irradiation of an argon-sparged dichloromethane solution of potassium benzyltrifluoroborate, benzalaniline, and diphenylphosphate in the presence of Ir-dF(CF3)-dtb at room temperature using blue LEDs (450 nm) yielded the expected addition product in 76% isolated yield; only traces of homocoupling products could be detected. Control experiments established that catalyst and light are both required for reaction; the elimination of diphenylphosphate led to a slightly lower yield. Light/dark experiments seemed to favor a single-cycle mechanism rather than a radical-chain mechanism.
