Multi-Site Reduction of Hexachlorophosphazene to Low-Valent PN Heterocycles and Extension to the Reduction of poly-Chlorophosphazene

Abstract

Facile one and two site reduction of hexachlorophosphazene using cyclic (alkyl)(amino)carbene substituents is shown to yield P-CAACMe-cyclo-(PNP(Cl)2NP(Cl)2N) 1 and P,P’-bis-CAACMe-cyclo-(PNPNP(Cl)2N) 2 (CAACMe=1-[2,6-bis(isopropyl)phenyl]-3,3,5,5-tetramethyl-2-pyrrolidinylidene). Compound 1 is characterized by its predominantly phosphorus centered HOMO, which results in typical phosphine-type nucleophilic and reductive reactivity; however, the resultant compounds of such reactions feature properties distinct from their classical phosphine analogues due to the CAAC centered LUMO, which acts as acceptor for both intramolecular interactions and photophysical excitations. In contrast, compound 2 exhibits π-conjugation spanning the endocyclic PNP moiety and the two CAACMe substituents, despite its non-planar structure. Treatment of 2 with [Cp*RuCl]4 results in the electrophilic displacement of one of the CAACMe¬ moieties by two Cp*RuCl fragments to yield the spirocyclic compound 3. Preliminary results show that the methodology used to reduce hexachlorophosphazene to 1 can be directly transposed to the regiospecific reduction of poly-chlorophosphazene, to yield poly-1, a fundamentally new class of inorganic polymer that possesses a phosphorus center with chemically active lone pairs in the main chain.