Generation and characterization of new fluoro-substituted carbenes

Singlet fluorocarbenes substituted with diphenylphosphanyl, phenylsulfanyl, and trimethylsilyl groups were generated upon photolysis of the corresponding tricyclo[4.3.1.0]decadiene precursors 1a-c. Diphenylphosphanyl fluoro carbene 2a was directly observed by transient UV-Vis spectroscopy. Its lifetime in several solvents ranged from 1 to 10 mus. A study of its reactivity toward methyl acrylate and tetramethylethylene along with DFT calculations did not indicate specific solvation of the carbene center. Fluorothiophenyl carbene 2b and fluorotrimethylsilyl carbene 2c were studied by their reaction with pyridine to form ylides and have lifetimes of 1 mus (cyclohexane) and 33 ns (carbon tetrachloride), respectively, at room temperature. Transient UV-Vis spectroscopy supported by DFT calculations showed that, in the case of fluorothiophenyl carbene 2b, carbene formation is in competition with the generation of the diradical intermediate formed by the cleavage of only a single C-C bond of the cyclopropane ring of the precursor.