BODIPY Photocatalyzed Beckmann Rearrangement and Hydrolysis of Oximes under Visible Light

A novel, efficient, and mild protocol for rearrangement of oximes to amides or hydrolyzing to ketone/aldehyde using a simple BODIPY dye as a photocatalyst and air as an oxidant via propagation reaction under visible-light irradiation is reported. The triplet excited state of BODIPY played a significant role in the catalytic process. It was found that the various substituted ketoximes, both with electron-withdrawing and electron-donating substituents, afforded the corresponding products with moderate to excellent yields, and the catalytic efficiency was up to 0.01 mol %.

Utilization of BODIPY-based redox events to manipulate the Lewis acidity of fluorescent boranes

This report describes the implementation of a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dye into the ligand framework of a borane. The redox-active nature of the BODIPY dye is utilized to generate a family of molecular boranes that are capable of exhibiting tunable Lewis acidities through BODIPY-based redox events.

Synthesis, Structure and Photophysical Properties of a New Class of Inherently Chiral Boron(III) Chelates-The tert-Leucine Complexes

A new family of boron(III) chelates is introduced whereby molecular chirality, confirmed by circular dichroism, is imported during synthesis such that isolation of the diastereoisomers does not require separation procedures. The photophysical properties of two members of the family have been examined: the N,O,O-salicylaldehyde-based derivative shows pronounced intramolecular charge-transfer character in fluid solution and is weakly fluorescent, with a large Stokes shift. The corresponding 2-methylamino-benzaldehyde-derived N,N,O-chelate absorbs and fluoresces in the visible region with a much smaller Stokes shift. Orange fluorescence is also observed for this compound as a cast film. Temperature-dependence studies show that decay of the fluorescent state is weakly activated but emission is less than quantitative at 77 K. Quite rare for boron(III)-based chelates, this derivative undergoes intersystem crossing to form a meta-stable triplet-excited state. X-ray crystal structures are reported for both compounds, along with simulated ECD spectra.

Synthesis and Characterization of Hydrazine-Appended BODIPY Dyes and the Related Aminomethyl Complexes

The synthesis and characterization of three new organic hydrazines containing BODIPY dyes is described. The respective aminomethyl complexes were also synthesized to aid in the assignment of the physical properties that were hydrazine-based vs. BODIPY-based. Incorporation of a BODIPY dye into an organic hydrazine introduced a reduction event (average value of -1.70 V vs. Cp₂Fe/Cp₂Fe⁺). Although two irreversible oxidation events were observed, it was unclear whether the oxidation events arose from BODIPY-based or amine/hydrazine-based oxidations. The respective BODIPY-appended hydrazine complexes exhibited excited state lifetimes on the order of 2-6 ns, suggesting the presence of a singlet excited state. The excited state lifetimes of the BODIPY-appended hydrazine complexes were about a factor of ten greater than the respective aminomethyl complexes. Computational analysis showed that by appending a BODIPY dye to a hydrazine fragment the hydrazine fragment becomes more susceptible to transfer H₂ equivalents as protons and hydrides as opposed to H-atoms, which occurs with common organic hydrazines. Computational analysis also revealed that the BODIPY-based redox events can be used to manipulate the mechanism for H₂ transfer from the BODIPY-appended hydrazine, where a BODIPY-based reduction favors H-atom transfer and a BODIPY-based oxidation favors proton transfer followed by hydride transfer.

Utilization of a Fluorescent Dye Molecule as a Proton and Electron Reservoir

Fluorescent dyes have been widely utilized as chemical sensors and in photodynamic therapy, but exploitation of their redox-active nature in chemical reactions has remained mostly unexplored. This report describes the isolation of a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-based radical. The redox-active nature of the BODIPY compound can be utilized in combination with a guanidine center, the basicity of which can be manipulated by greater than 14 pK_a units, to promote the conversion of protons and electrons into H-atoms for transfer to substrate molecules.

Influence of Lewis acid strength on hydride transfer to unsaturated substrates

Coordination of a Lewis acid to a substrate molecule increases its ability to accept a hydride between 20 and 70 kcal mol⁻¹.