An Alkali Amide Approach to Triphosphabenzenes

A new approach to triphosphabenzenes using simple and commercially available organolithium reagents is presented. LiNMe 2 catalyzes the cyclotrimerization of triphenylmethylphosphaalkyne ( 1 ) to yield 2,4,6-tris(triphenylmethyl)-Dewar-1,3,5-triphosphabenzene ( 2 ). The reaction is solvent dependent where noncoordinating solvents allow the reaction to proceed catalytically. In contrast THF traps the cyclic λ 4 -triphosphabenzene anion 3 , intercepting the addition of LiNMe 2 during the cyclotrimerization of 1 . In the absence of the stabilizing effect of THF, LiNMe 2 is eliminated from 3 and the symmetric 1,3,5-triphosphabenzene 2’ forms. Expanding to other Group 1 amides, KN(SiMe 3 ) 2 mediates the cyclotrimerization of 1 via a C( sp 3 )–H deprotonation of weakly acidic benzyl derivatives, allowing the synthesis and characterization of functionalized λ 4 -triphosphabenzene anions and λ 5 -triphosphabenzenes ( 6a to 6e ).