Aromatic C-F activation by complexes containing the {Pt2S2} core via nucleophilic substitution: a combined experimental and theoretical study.

The C-F bond activation of perfluorobenzene and perfluoropyridine have been achieved by means of the complex [Pt(2)(mu-S)(2)(dppp)(2)], where dppp denotes 1,3-bis(diphenylphosphino)propane. The reaction with the first substrate requires a long time (five days) and high temperature (reflux in toluene) to yield [Pt(o-S(2)C(6)F(4))(dppp)] and [Pt(3)(mu(3)-S)(2)(dppp)(3)]F(2), and involves replacement of two fluorides in the ortho position. In contrast, the reaction with perfluoropyridine is much faster (15 min at 0 degrees C) yielding [Pt(2)(mu-S){mu-(p-SC(5)F(4)N)}(dppp)(2)]F, which implies the C-F activation in the para position with respect the pyridine nitrogen. The mechanism of both reactions has been studied computationally and the geometries of the transition states are consistent with an S(N)Ar mechanism where a sulfido bridging ligand replaces the fluoride anion. The energy barriers corresponding to the first and the second fluoride substitution are 131.7 and 137.1 kJ mol(-1) for perfluorobenzene and 85.9 and 142.7 kJ mol(-1) for perfluoropyridine, respectively. The different energy barrier of the first substitution explains the different experimental conditions required and the various products obtained for these reactions.