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.