Bis(imido)vanadium(V)-Catalyzed [2+2+1] Coupling of Alkynes and Azobenzenes Giving Multisubstituted Pyrroles

The
combination of VCl3(THF)3 and N,N-bis­(trimethylsilyl)­aniline (1a)
is an efficient catalyst for the [2+2+1] coupling reaction of alkynes
and azobenzenes, giving multisubstituted pyrroles. A plausible reaction
mechanism involves the generation of a mono­(imido)­vanadium­(III) species
as an initiation step, where 1a served as an imido source
with concomitant release of 2 equiv of ClSiMe3, followed
by a reaction with azobenzene to form a catalytically active bis­(imido)­vanadium­(V)
species via NN bond cleavage.