FLUOROPHOSPHAALKENES–PREPARATION AND REACTIVITY

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Abstract
A novel preparative route to perfluoroheteroalkenes F3CE[dbnd]CF2 (E = P, As) and E'[dbnd]CF2 (E' = S, Se) has been developed using the trimethyltin compounds Me2SnE(CF3)2 and Me3SnE'CF3 as precursors. After a short information about the characterization of these heteroalkenes, the results of self-addition, HX-additon and [2 + 4] cycloaddition reactions of F3CP[dbnd]CF2 (1) [and in part of F3CAs[dbnd]CF2 (2)] are presented and discussed. A one-pot procedure could be developed for the Diels-Alder type reactions of 1 and 2, keeping a mixture of Me3SnE(CF3)2 and the corresponding diene at 70°C until the 19F signals of the tin compound disappeared. The enthalpy of dissociation of the dimer (CF3PCF2)2 as well as that of the retrodiene cleavage of the [2 + 4] cycloadduct, formed from 1 and cyclopentadiene, are deduced from appearance potentials and used for an estimate of the PC σ- and π-bond energy of 1. A one-pot process for the production of the labile diphosphene F3P[dbnd]PCF3 (23) and its trapping by dienes are reported. The observed reactivity of 1 and 23 support the view that these compounds show a remarkable similarity to alkenes.