Aluminum chloride-catalyzed reactions of ferrocene with phosphorus(III) amides. Novel coordination of the PN system

Abstract In aluminum chloride-catalyzed reactions with ferrocene, P III compounds show reactivities in the order, PCl 3 ⪡ R 2 NPCl 2 > (R 2 N) 2 PCl > (R 2 N) 3 P, revealing that active intermediate species are formed by the coordination of aluminum chloride not to phosphorus but to nitrogen. Evidence is presented which supports this, and indicates that aluminum chloride cleaves the PN bond via bonding to nitrogen, generating PCl. HCl, formed as by-product of the Friedel-Crafts reactions, is not a factor in the cleavage of the PN bond. Catalysis and inhibition of the reactions are discussed in terms of a mechanism based on the concept of a dimolar aluminum chloride complex of a donor species such as R 2 NPCl 2 or R 3 N. The reactions are seen to generate (Fc) 3 P both by a stepwise electrophilic process and by disproportionation of (Fc) 2 PCl. The coordination of AlCl 3 to nitrogen of PN is rationalized on the basis of bond energetics and the unavailability of electrons for back-bonding to phosphorus. Several new phosphorus amides of ferrocene are reported.