Facile Access to the Pnictocenium Ions [Cp*ECl]+ (E=P, As) and [(Cp*)₂P]+: Chloride Ion Affinity of Al(ORF)₃?

摘要

The pnictocenium salts [Cp*PCl]+[μCl]− (1 a), [Cp*PCl]+[ClAl(ORF)₃]− (1 b), [Cp*AsCl]+[ClAl(ORF)₃]− (2), and [(Cp*)₂P]+[μCl]− (3), in which Cp*=Me₅C₅, μCl=(FRO)₃AlClAl(ORF)₃, and ORF=OC(CF₃)₃, were prepared by halide abstraction from the respective halopnictines with the Lewis superacid PhF→Al(ORF)₃.1 The X-ray crystal structures of 1 a, 2, and 3 established that in the half as well as in the sandwich cations the Cp* rings are attached in an η2-fashion. By using one or two equivalents of the Lewis acid, the two new weakly coordinating anions [μCl]− and [ClAl(ORF)₃]− resulted. They also stabilize the highly reactive cations in PhF or 1,2-F₂C₆H₄ solution at room temperature. The chloride ion affinities (CIAs) of a range of classical strong Lewis acids were also investigated. The calculations are based on a set of isodesmic BP86/SV(P) reactions and a non-isodesmic reference reaction assessed at the G3MP2 level.