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

Abstract

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.