Ethynylcobaltocenium compounds as precursors for bridged, heteronuclear oligometallocenes

Abstract

A general procedure for introducing substituents into cationic sandwich complexes by nucleophilic attack of suitable carbanions and subsequent hydride abstraction has been applied to the preparation of ethynyl-substituted cobaltocene species. Ethynylcobaltocenium hexafluorophosphate, trimethylsilylethynylcobaltocenium hexafluorophosphate, and salts of ferrocenylethynylcobaltocenium, a rigidly-bridged, conjugated heteronuclear bimetallocene, have been prepared. These compounds and isolated exo-diene intermediates have been characterized by NMR and IR spectroscopy, mass spectrometry and cyclic voltammetry. The new two-centered sandwich cation ferrocenylethynylcobaltocenium exhibits diamagnetism, indicating a situation not involving asymmetric averaging of the formal oxidation states on the NMR time scale. The electrochemical potentials and halfwave separations fall within the expected ranges.