The substitution of the chlorido ligand of bis(η 5 :η 1 -(di-p-tolyl)-pentafulvene)niobium chloride by reaction with (trimethylsilyl)methyllithium is followed by α-C−H bond activation. Because of the π-η 5 :σ-η 1 coordination mode, the exocyclic carbon atom of the pentafulvene ligand is strongly nucleophilic and therefore protonated, and the niobium alkylidene species (3) is isolated. The formed complex 3 shows cooperating reactions of the remaining pentafulvene and the alkylidene ligand in activating different E−H bonds. Under mild conditions, terminal imido complexes (4) and a hydrazido complex (5) are obtained by double N−H bond splitting. By the reaction of 3 with Nmethylaniline, a niobaaziridine ( 6) is formed via simultaneous N−H and C−H bond activation. By deuterium labeling, the N−H bond can be assigned to the pentafulvene moiety and the C−H bond to the alkylidene carbon center.