Photo/Thermally Induced Reversible (De-)Coordination of the Perfluorinated Cp* Ligand in Metallocenes

The electron-deficient ferrocene [Fe(C5H5)(C5(CF3)5)] is complemented by the synthesis and full characterisation of the analogous bench-stable ruthenocene [Ru(C5H5)(C5(CF3)5)]. These complexes have been studied with respect to the substitution lability of the perfluorinated Cp* ligand under mild conditions. Photolysis of the metallocenes in MeCN converted the [C5(CF3)5]- ligand into a weakly coordinating anion. This gave access to the highly reactive piano-stool complexes [M(C5H5)(MeCN)3][C5(CF3)5] (M = Fe, Ru). The unstable iron half-sandwich complex dismutates under formation of [Fe(C5H5)2] and [Fe(MeCN)6][C5(CF3)5]2. It was trapped by the chelating diphosphine DPPE and isolated as thermally stable [Fe(C5H5)(DPPE)(MeCN)][C5(CF3)5]. For [Ru(C5H5)(MeCN)3][C5(CF3)5] a thermally induced backreaction to ruthenocene is observed. This represents the first example of a reversible dissociation and recoordination of a cyclopentadienyl ligand, initiated by light and heat.