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

The substitution of the chlorido ligand of bis(eta(5):eta(1)-(di-p-tolyl)-pentafulvene)niobium chloride by reaction with (trimethylsilyl ) me thyllithium is followed by alpha-C-H bond activation. Because of the pi-eta(5):sigma-eta(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 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.