Aluminium-27 N.M.R. Studies of Aluminum Fluoro Complexes in Dichloromethane Solution: Evidence for the Tetrafluoroaluminate Anion

Abstract

Mixed aluminium chloro/fluoro anions are formed in dichloromethane solution by the interaction of AICl₃ and [Ph₃PhCH₂P][H₂F₃]. Aluminium-27 n.m.r. studies are restricted to the stoichiometric ranges F/AI from 1 : 1 to 3 : 1 and F/AI > 8 : 1. Between these limits rapid precipitation reactions occur. In the fluoride-rich stoichiometric range there is rapid exchange on the n.m.r. time scale between the aluminium fluoro anion and free fluoride, so that a direct identification of the species by the multiplicity of the resonance is not possible. Indirect evidence strongly suggests that the aluminium species is [AIF₄. In the F/AI stoichiometry range from 1 : 1 to 3 : 1 aluminium-27 resonances were observed for all the other possible [AICI_xF₄-_x]- species. Studies on the aluminium \iodo/fluoro system support the identification of [AIF₄]-, but the system is labile and the mixed iodo/fluoro species undergo rapid disproportionation.