Fluorinated Sulfilimino Iminiums: Efficient and Versatile Sources of Perfluoroalkyl Radicals under Photoredox Catalysis

Reported herein is the use of S‐perfluoroalkyl sulfilimino iminiums as a new source of R_F radicals under visible‐light photoredox catalysis (R_F=CF₃, C₄F₉, CF₂Br, CFCl₂). These shelf‐stable perfluoroalkyl reagents, readily prepared on gram scale from the corresponding sulfoxide using a one‐pot procedure, allow the efficient photoredox‐induced oxyperfluoroalkylation of various alkenes using fac‐Ir(ppy)₃ as the photocatalyst. Importantly, spin‐trapping/electron paramagnetic resonance experiments were carried out to characterize all the radical intermediates involved in this radical/cationic process.     

Generation and EPR Spectroscopy of the First Silenyl Radicals,R2C=Si.−R: Experiment and Theory

The first two persistent silenyl radicals (R₂C=Si^.?R), with a half‐life (t_1/2) of about 30 min, were generated and characterized by electron paramagnetic resonance (EPR) spectroscopy. The large hyperfine coupling constants (hfccs) (a(²⁹Si_α)=137.5–148.0 G) indicate that the unpaired electron has substantial s character. DFT calculations, which are in good agreement with the experimentally observed hfccs, predict a strongly bent structure (?C=Si?R=134.7–140.7°). In contrast, the analogous vinyl radical, R₂C=C^.?R (t_1/2≈3 h), exhibits a small hfcc (a(¹³C_α)=26.6 G) and has a nearly linear geometry (?C=C?R=168.7°).     

A 19th Century “Ideal” Oil Paint Medium: A Complex Hybrid Organic–Inorganic Gel

British 19th century painters such as J. M. W. Turner, commonly modified the properties of their paint by using gels called “gumtions”. These gels allowed them to easily tune the paint handling and drying properties. The fascinating properties of these “gumtions” were obtained by adding lead acetate to a ternary system based on mastic resin, linseed oil and turpentine. Herein, we report and investigate in depth the rheological properties of these gels as well as their structure at a molecular and supra‐molecular scale.     

Fast Heavy‐Atom Tunneling in Trifluoroacetyl Nitrene

Chemical reactions involving quantum mechanical tunneling (QMT) increasingly attract the attention of scientists. In contrast to the hydrogen‐tunneling as frequently observed in chemistry and biology, tunneling solely by heavy atoms is rare. Herein, we report heavy‐atom tunneling in trifluoroacetyl nitrene, CF₃C(O)N. The carbonyl nitrene CF₃C(O)N in the triplet ground state was generated in cryogenic matrices by laser (193 or 266 nm) photolysis of CF₃C(O)N₃ and characterized by IR and EPR spectroscopy. In contrast to the theoretically predicted activation barriers (>10 kcal mol⁻¹), CF₃C(O)N undergoes rapid rearrangement into CF₃NCO with half‐life times of less than 10 min and unprecedentedly large ¹⁴N/¹⁵N kinetic isotope effects (1.18–1.33) in solid Ar, Ne, and N₂ matrices even at 2.8 K. The tunneling disappearance of CF₃C(O)N becomes much slower in the chemically active toluene and in 2‐methyltetrahydrofuran at 5 K.