On the Catalytic Hydrodefluorination of Fluoroaromatics Using Nickel Complexes: The True Role of the Phosphine

Homogeneous catalytic hydrodefluorination (HDF) of fluoroaromatics
under thermal conditions was achieved using nickel(0) compounds of
the type [(dippe)­Ni­(η2-C6F6‑nHn)]
where n = 0–2, as the catalytic precursors.
These complexes were prepared in situ by reacting
the compound [(dippe)­Ni­(μ-H)]2 with the respective fluoroaromatic substrate. HDF seems to
occur homogeneously, as tested by mercury drop experiments, producing
the hydrodefluorinated products. However, despite previous findings
by other groups, we found that these HDF reactions were actually the
result of direct reaction of the alkylphosphine with the fluoroaromatic
substrate. This metal- and silane-free system is the first reported
example of a phosphine being able to hydrodefluorinate on its own.