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

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Apr 21st, 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.