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

Abstract The first two persistent silenyl radicals (R 2 C=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 ( 29 Si 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, R 2 C=C . −R ( t 1/2 ≈3 h), exhibits a small hfcc ( a ( 13 C α )=26.6 G) and has a nearly linear geometry (∡C=C−R=168.7°).