Addition and NN bond cleavage of diazo-compounds by phosphino-phosphenium cations.

The phosphino-phosphenium cation (PPC) [Ph 3 PPPh 2 ][GaCl 4 ] reacts as a frustrated Lewis pair to add across the NN bond of ( t BuO 2 CN) 2 . In contrast, photolytical addition [Ph 2 ClPPPh 2 ][GaCl 4 ] to (RN) 2 results in cleavage of the NN bond affording [Ph 2 P(μ-NR) 2 PPh 2 Cl][GaCl 4 ] (R = Ph 2, C 6 H 4 Cl 3 ). While the chloride of 2 is replaced with N 3 or CN via reaction with Me 3 SiN 3 or t BuNC respectively, reaction with (C 6 F 5 ) 2 BH effects ring opening to give [HN(Ph)PPh 2 (μ-NPh)PPh 2 ][GaCl 4 ] 7. This reactivity demonstrates that PPCs behave as FLPs to effect either addition or cleavage of NN double bonds.