N–H and N–C Bond Formation with an N2‑Derived Dihafnium μ‑Nitrido Complex

Exposure of the base-free isocyanato dihafnocene μ-nitrido complex prepared from CO-induced N2 cleavage to a dihydrogen atmosphere resulted in rapid 1,2-addition across the hafnium–nitrogen bond followed by insertion of the terminal isocyanate ligand into the putative hafnium hydride ligand and formed a bridging formamide ligand. Terminal alkynes and sterically hindered allenes underwent preferential addition of a C–H bond across the hafnium nitride fragment and resulted in isolation of the μ-imido acetylide and allenyl dihafnocene complexes, respectively. Reducing the steric profile of the allene enabled N–C rather than N–H bond-forming chemistry arising from cycloaddition of the π system. In the presence of additional allene, the resulting azahafnacyclobutanes underwent exchange, establishing the reversibility of the N–C bond forming reaction. Ketones with enolizable hydrogens, amines, and guanidines underwent rapid deprotonation upon addition to the isocyanato dihafnocene μ-nitrido complex and offer a route to N–H bond formation, as well as allowing isolation of a rare example of a parent amido compound. The preference of the dihafnium nitrido system for N–H over N–C bond formation was explored by treatment with styrene oxide, which afforded exclusively the E2 elimination product rather than the expected 1,2-amino alkoxide complex.