Dihalides of Sterically Constrained Tricyclic Phosphines, Lewis Acidity and Fluoride Affinity, Chloride Abstraction, and a Phosphonium Cation, Dimethylphosphorane

Abstract

Treatment of the trilithium compounds 3 with PCl3 afforded sterically constrained tricyclic phosphines with annulated five‐ (2 ×) and six‐membered rings and the P atoms in the bridgehead positions (2a, vinylic SiMe2Ph; 2b, vinylic SiMe3 groups). Their AuCl complexes (4) were used for an estimation of the buried volumes (4b: %V = 46 %). Reactions of 2b with XeF2 or SO2Cl2 afforded PX2 derivatives [X = F (5b), Cl (6b)]. Crystal structure determinations including the recently reported difluorides and diiodides of 2a (5a and 7) allow a systematic comparison of structural details. The P atoms have trigonal bipyramidal to square pyramidal surroundings. The PF2 phosphorane 5a behaves as a Lewis acid and coordinates F– to yield a phosphate anion (8) with a PF3C3 molecular centre, while Cl– abstraction from 3a afforded an unstable phosphonium cation (9). Unusual methylphosphoranes with one or two methyl groups attached to phosphorus were obtained by reactions of the dihalides 5a or 6a with methyllithium.