An unsymmetrical phosphonium diylide with a fluorenylidene subunit and its lithium complexes

The phosphonium ylide MePh₂P(flu) (3) (flu = C₁₃H₈, fluorenylidene) was conveniently prepared by reaction of Ph₂P(fluH) (1) (fluH = C₁₃H₉, fluorenyl) with iodomethane, followed by subsequent dehydrohalogenation of the resulting phosphonium salt MePh₂P(fluH)]I (2) by potassium tert-butoxide. Compound 3 was further deprotonated by n-butyllithium, yielding the corresponding lithium complex Li{CH₂PPh₂(flu)}(tmeda)] (4) in presence of N,N,N′,N′-tetramethylethylenediamine (tmeda). This mononuclear lithium compound contains the monoanionic chelating diylidic ligand. An exchange of the neutral bidentate tmeda by tridentate N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (pmdta) enforces a change in coordination mode. Consequently, the diylide is monodentate in Li{CH₂PPh₂(flu)}(pmdta)] (5). Compounds 1–5 were characterized by NMR spectroscopy and single-crystal X-ray diffraction experiments.