Cooperative Reactions of Pentafulvene Niobium Complexes: Formation of Alkylidene, Imido, Hydrazido, and Niobaaziridine Complexes

The substitution of the chlorido ligand of bis(η5:η1-(di-p-tolyl)-pentafulvene)niobium chloride by reaction with (trimethylsilyl)methyllithium is followed by α-C–H bond activation. Because of the π-η5:σ-η1 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 N-methylaniline, 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.