Abstract:Photoredox catalysis provides many green opportunities for radical-mediated synthetic transformations. However, the determination of the underlying mechanisms has been challenging due to lack of quantitative methods that can be easily implemented in synthetic labs, where this research tends to be centered. We report here on the development, characterization and calibration of a novel actinometer based on the photocatalyst tris(2,2′-bipyridyl)ruthenium(II) chloride (Ru(bpy)3Cl2). By using the same molecule as t… Show more
“…11 This apparent quantum yield is more formally known as photonic efficiency (ζ p ) and can be described as equation (1). In order to calculate I 0 , we employed our recently developed Ru(bpy) 3 Cl 2 visible-light actinometer 12 , where we were able to calculate that the I 0 for the 460 nm LED set-up employed was 4.7±0.1 × 10 −7 mol hν s −1 (see section H of SI). In order to calculate the ζ p , initial reaction rates after 1 hour of irradiation were determined (Figure 2).…”
Indole alkaloids represent an important class of molecules, with many naturally occurring derivatives possessing significant biological activity. One area that requires further development in the synthesis of indole derivatives is the Diels–Alder reaction. In this work, we expand on our previously developed heterogeneous protocol for the [4+2] cycloaddition of indoles and electron-rich dienes mediated by platinum nanoparticles supported on titanium dioxide semiconductor particles (Pt(0.2%)@TiO2) with visible-light irradiation. This reaction proceeds with broad scope and is more efficient per incident photon than the previous homogeneous method, and the catalyst can be easily recycled and reused.
“…11 This apparent quantum yield is more formally known as photonic efficiency (ζ p ) and can be described as equation (1). In order to calculate I 0 , we employed our recently developed Ru(bpy) 3 Cl 2 visible-light actinometer 12 , where we were able to calculate that the I 0 for the 460 nm LED set-up employed was 4.7±0.1 × 10 −7 mol hν s −1 (see section H of SI). In order to calculate the ζ p , initial reaction rates after 1 hour of irradiation were determined (Figure 2).…”
Indole alkaloids represent an important class of molecules, with many naturally occurring derivatives possessing significant biological activity. One area that requires further development in the synthesis of indole derivatives is the Diels–Alder reaction. In this work, we expand on our previously developed heterogeneous protocol for the [4+2] cycloaddition of indoles and electron-rich dienes mediated by platinum nanoparticles supported on titanium dioxide semiconductor particles (Pt(0.2%)@TiO2) with visible-light irradiation. This reaction proceeds with broad scope and is more efficient per incident photon than the previous homogeneous method, and the catalyst can be easily recycled and reused.
“…Both of these chemicals are highly phosphorescent and can be chemically engineered; the chloride in [Ru(bpy) 3 ]Cl 2 can be replaced with anions such as hexafluorophosphate. Recently, [Ru(bpy) 3 ]Cl 2 was used as a photocatalyst with photochemical and redox properties, as well as an actinometer 13 .Figure 3Imaging comparison between traditional microscopy and optimized optics. Traditional microscopy (left) does not have the illumination and setup optimized in respect of the optical activity of particles, compared to our method (right), which focuses on optimized background environment, and an innovative microscope objective combined with a specific illumination that permit the particle to self-distribute the light rays internally for better surface observation, rather than acting as a prism with uniform reflections.…”
Scanning electron microscopy and X-ray microtomography are useful methods for high resolution shape imaging. Visible microscopy is also common, however, developing a low-cost and customizable system for surface and shape investigation of optically active particles is challenging. In this work, we demonstrate an assembly offering good light sensitivity, flexibility of illumination and contrasts from varying angles. The design was applied, together with recent programs for focus-stacking, to analyze crystals of taurine, L-glutamic acid, acetylsalicylic acid, and copper sulfate, along with digital 3D-360° modelling of phosphorescent [Ru(bpy)3]Cl2 and strontium aluminate particles. We further tested the approach for real time monitoring of size, shape and texture analysis of fat filled milk particles and acid whey powders. The findings show proof of concept for detailed feature imaging of particles directly from the process environment.
“…Of the various reaction components, only TMEDA was shown to efficiently quench [Ru*(bpy) 3 ] 2+ ( k q =3.46×10 7 m −1 s −1 with τ 0 =1100 ns) [Eq. (2); Scheme C] . From this data, we calculated a quenching fraction of 95 % [Eq.…”
Photocatalytic radical trifluoromethylation strategies have impacted the synthesis of trifluoromethyl-containing molecules. However, mechanistic aspects concerning such transformations remain poorly understood. Here, we describe in detail the mechanism of the visible-light photocatalytic trifluoromethylation of N-methylpyrrole with gaseous CF3 I in flow. The use of continuous-flow microreactor technology allowed for the determination of different important parameters with high precision (e.g., photon flux, quantum yield, reaction rate constants) and for the handling of CF3 I in a convenient manner. Our data indicates that the reaction occurs through a reductive quenching mechanism and that there is no radical chain process present.
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