Donor-stabilised cations, phosphinamide anions, and unusual oxidative cyclisation products from halogenated phosphoranimines and phosphinimines with a bulky 2,4,6-tri-tert-butylphenyl substituent at nitrogen

Abstract

New aspects of the chemistry of the phosphoranimine Cl₃PNMes* (Mes* = 2,4,6-tri-tert-butylphenyl) (7) and the phosphinimine ClPNMes* (2) have been explored. A cationic derivative of 7 was prepared from the reaction between this species and DMAP (DMAP = 4-dimethylaminopyridine) in the presence of the halide abstraction agent AgOTf (OTf = OSO₃CF₃) which yielded the donor-stabilized cation [DMAP–PCl₂NMes*]⁺ ([9]⁺). When treated with tertiary phosphinesⁿBu₃P or Ph₃P, 7 was found to undergo a reductive dechlorination reaction to yield 2 and dichlorophosphoranes R₃PCl₂ (R = ⁿBu (13a), Ph (13b)). The phosphinimine 2 reacts with Cl⁻ sources to form the novel dichlorophosphinamide anion [Cl₂PNMes*]⁻ ([14]⁻) which was characterized in solution. Treatment of [Ph₄P][14], generated in situ, with GaCl₃ or MeOTf regenerated 2 and provided further evidence for the formation of the anion [14]⁻. In addition, phosphoranimine 2 was found to undergo an unexpected oxidative cyclization reaction when treated with the oxygen transfer agent pyridine-N-oxide to yield a P-chlorophosphoryl-ox-3-azoline (18).