NH insertion to a phosphoazonium cation gives an alpha-phosphenium product

An α-cationic phosphine was isolated in good yield from the reaction of [Mes*NP][GaCl 4 ] (Mes* = 2,4,6-tri- tert-butylphenyl) and Dipp 2 NacNacH (Dipp 2 NacNac = [DippNC(CH 3 )] 2 CH (Dipp = 2,6-di- iso-propylphenyl)). The product was characterized spectroscopically and crystallographically. In the product, the phosphorus atom is incorporated within the NacNac ring, while maintaining a bond to the nitrogen atom of the NMes* group. A similar reaction involving IPr=NH (IPr = [DippN(CH)] 2 C) and [Mes*NP][GaCl 4 ] gave a much different product. A few crystals of [IPr=NH 2 ][GaCl 4 ] were isolated and characterized using only X-ray crystallography. The anticipated neutral phosphine product could not be recovered from attempted deprotonations of the α-cationic phosphenium salt.