Improved Synthetic Route to Unsymmetrically Substituted Phosphinimino-phosphonium Salts. Crystal Structure of Tri-w-butyl- [tris(diethylamino)phosphinimino]phosphonium Chloride

Symmetrically substituted phosphinimino-phos­ phonium salts [R3PNPR3]X have been known for a long time, and their unusual stability towards acids and bases was demonstrated by the work of Ap­ pel and Hauss [1], and Schmidbaur and Jonas [2]. The delocalisation of the positive charge in the PNP skeleton and the shielding by the substituents are the main reason for the use of phosphinimino-phos­ phonium cations as ideal counterions for the sta­ bilisation of unstable anions [3]. In particular, the bis(triphenylphosphin)iminium cation has found extensive use as a large non-interacting organic cation for the crystallisation of anionic species, notably metal carbonyl cluster anions [4]. Previ­ ously we reported the preparation of unsymmetri­ cally substituted phosphinimino-phosphonium salts of the type [Bu"3PNPR3]X (R3 = Me3, Me(NMe2)2, (Me2N)3, (Et2N)3; X = I, PFö) using the fluorophosphonium salt [Bu^PFJBr as starting mate­ rial [5], but structural information was lacking. In this paper we describe an improved synthetic route to the unsymmetrically substituted phosphiniminophosphonium cation [Bu”3PNP(NEt2)3]+ with chlo­ ride as counterion and its characterisation by Xray crystal structure analysis. The tri-n-butylchlorophosphonium chloride 1 served as starting material; it can easily be prepared by chlorination of tri-nbutylphosphine with phosphorus pentachloride un­ der mild conditions [6]. Treatment of 1 with N-trimethylsilyl-tris(diethylamino)-phosphinimine 2 af­ forded the title compound 3 as a colourless solid: Bu"3P + PC15 — [Bun3PCl]+C r + PCI3 1