Fluorenylidene: Kinetics and Mechanism

Article abstract of DOI:10.1021/ja00320a001

Laser irradiation of 9-diazafluorene in solution leads to the formation of a transient species with λ_max=470 nm that has been characterized as the triplet carbene and is believed to be in thermal equilibrium with the singlet state, which lies within a few kcal/mol.The singlet carbene is frequently more reactive and tends to dominate the chemistry.For example, in hydrogen donors, the triplet state abstracts hydrogen leading to the 9-fluorenyl radical, which is the only species detected in the flash experiments.However, product studies demonstrate that the predominant reaction path is the insertion of the singlet into C-H bonds (e.g., in cyclohexane), a process that is transparent to the technique of nanosecond laser photolysis.Irradiation of 9-diazofluorene in nitrile solvents results in carbene addition to the nitrile function, leading to nitrile ylides that react rapidly with electron-deficient olefins and present a characteristic absorption band at ca. 400 nm.The singlet carbene has a lifetime of <=5 ns and obeys the Skell-Woodworth rules.