Preparation and properties of stable protonation products of permethylmetallocenecarbaldehydes (M = Fe, Ru, Os)

Abstract

The products ofO-protonation of metallocenecarbaldehydes C₅Me₅MC₅Me₄CHO (M = Fe, Ru, Os) with HBF₄ and CF₃COOH were obtained for the first time, the adducts [C₅Me₅MC₅Me₄CH(OH)]⁺BF⁻ being isolated in a pure state. The structures of the adducts depend on the nature of the metal and the anion and are governed by the correlation between their basicities. For example, the Fe-containing adducts have an open fulvenoid structure with an interionic hydrogen bond irrespective of the nature of the anion X (X = BF₄ ⁻, CF₃COO⁻). In the case of the Ru- and Os-containing adducts in which the metal atoms are more basic than iron, the competition between the metal atom and the anion for the formation of a hydrogen bond with the OH group is clearly manifested in the IR and¹H NMR spectra. In the presence of the weakly basic BF₄ ⁻ anion, a cyclic structure with an intramolecular M...HO hydrogen bond is formed, while in the presence of a more basic F⁻ or CF₃COO⁻ anion. it transforms to the open fulvenoid structure with an interionic hydrogen bond. The structures of the compounds obtained were determined by IR and¹H NMR spectra, and the structure of the (C₅Me₅RuC₅Me₄CHOH)⁺...F⁻ salt was proved by X-ray diffraction analysis.