Unsaturated Organic Derivatives of Phosphaferrocene – Synthesis and Reactivity of Vinyl- and Alkynylphosphaferrocenes

Abstract

Starting from 2-formyl-3,4-dimethylphosphaferrocene, a series of vinyl-substituted phosphaferrocenes was prepared by Wittig and related olefination reactions. The parent 3,4-dimethyl-2-vinylphosphaferrocene (2) could be selectively converted to either the terminal or branched alcohols 8b and 8a by hydroboration/oxidation or protonation in aqueous solution, respectively. Elimination of HBr from 2-bromovinylphosphaferrocene 9 provided access to the 2-ethynylphosphaferrocene derivative 10, which could be converted to other alkynes by deprotonation and electrophilic quench. Additionally, the syntheses of the 2-cyano- (15) and 2-(ethoxycarbonyl)phosphaferrocene derivative 13 are reported. Several new phosphaferrocenes were converted into their respective Fe(CO)₄ complexes, which were investigated by IR spectroscopy. The CO stretching vibrations were found to depend on the nature of the substituent in the 2-position and the cyano compound 15 was identified as the least electron-donating ligand. Reaction of the alkynylphosphaferrocenes 10 and 11 with Co₂(CO)₈ afforded the respective dimetallatetrahedrane complexes 24 and 25. The molecular structures of compounds 12, 21 and 25 have been determined by X-ray diffraction analysis.