N₂ hydrogenation from activated end-on bis(indenyl) zirconium dinitrogen complexes

Sodium amalgam reduction of the bis(indenyl)zirconium dihalide complexes, (η⁵-C₉H₅-1-ⁱPr-3-Me)₂ZrX₂ (X = Cl, Br, I), yielded the corresponding end-on dinitrogen complexes, [(η⁵-C₉H₅-1-ⁱPr-3-Me)₂Zr(NaX)]₂(μ₂, η¹, η¹-N₂), with inclusion of 1 equiv of salt per zirconocene. The solid state structures of the chloro and iodo congeners establish short Zr=N and elongated N-N bonds, consistent with modest to strong activation of the coordinated dinitrogen molecule. Exposure of the N₂ compounds to 1 atm of dihydrogenresulted in rapid N-H bond formation to yield a hydrido zirconocene hydrazido compound concomitant with salt elimination. These studies establish a new structural type of zirconocene dinitrogen complex and demonstrate that side-on coordination of the N₂ ligand in the ground state is not a prerequisite for dinitrogen hydrogenation.