THE CHEMISTRY OF YLIDS: XV. MECHANISM OF THE REACTION OF IMINOPHOSPHORANES WITH CARBONYL COMPOUNDS

Abstract

The pK_a values of two series of iminophosphoranes, N-(substituted phenyl)-iminotriphenylphosphoranes (VI) and N-phenyliminotri-(substituted phenyl)-phosphoranes (VII), have been correlated with σ⁰ and σ, respectively, giving ρ values of +3.5 and +9.3. A kinetic study of the reaction of VI and VII with benzaldehydes indicates that a betaine intermediate (V) is involved. The rate-limiting step of the reaction changes, the result of a delicate balance between the nucleophilicity of the nitrogen atom and the electrophilicity of the phosphorus atom. The involvement of dπ–pπ bonding is indicated.