Stimulus-responsive metallocenes: a photo/thermal switch enabled by the perfluorinated Cp* ligand.

The electron-deficient ferrocene [Fe(CH)(C(CF))] is complemented by the synthesis and full characterisation of the analogous bench-stable ruthenocene [Ru(CH)(C(CF))]. 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 [C(CF)] ligand into a weakly coordinating anion. This gave access to the highly reactive piano-stool complexes [M(CH)(MeCN)][C(CF)] (M = Fe, Ru). The unstable iron half-sandwich complex dismutates under formation of [Fe(CH)] and [Fe(MeCN)][C(CF)]. It was trapped by the chelating diphosphine DPPE and isolated as thermally stable [Fe(CH)(DPPE)(MeCN)][C(CF)]. For [Ru(CH)(MeCN)][C(CF)] 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.