Zirconium Hydrazides as Metallanitrene Synthons: Release of Molecular N₂ from a Hydrazinediido Complex Induced by Oxidative N–N Bond Cleavage

The N–N bond in the zirconium hydrazinediido(2−) complex [Zr­(N₂^TBSN_py)­(NNPh₂)­(py)] (1) is readily cleaved by one-electron oxidation. Reacting [Zr­(N₂^TBSN_py)­(NNPh₂)­(py)] (1) with 0.5 molar equiv of iodine led to the release of molecular N₂ and yielded the mixed diphenylamido/iodo complex [Zr­(N₂^TBSN_pyNPh₂)­(I)] (2). Exposure of hydrazinediide 1 to an excess of iodine resulted in further oxidation of the diphenylamido ligand, yielding the diiodo complex 3 and tetraphenylhydrazine. Similar reactivity was observed in the reaction of 1 with diphenyl diselenide and diaryl disulfides, which reacted to give the corresponding diphenylamido/arylchalcogenido complexes [Zr­(N₂^TBSN_pyNPh₂)­(SePh)] (4a) and [Zr­(N₂^TBSN_py)­(NPh₂)­(SAr)] (Ar = Ph (4b), C₆F₅ (4c)) along with N₂. The reactions were also carried out on an NMR scale with a ¹⁵N_α-labeled hydrazido complex (1-¹⁵N). In all cases a single ¹⁵N NMR resonance at 310.16 ppm, assigned to ¹⁵N₂, indicated the formation of dinitrogen from the N_α atom in the hydrazide. A crossover labeling experiment employing a 1:1 mixture of 1 and ¹⁵N_α-labeled 1-¹⁵N revealed that the isotope distribution is, as expected, statistical 1:2:1 (¹⁴N₂: ^14/15N₂: ¹⁵N₂), which is consistent with a reaction pathway involving a dinuclear intermediate in the dinitrogen-forming step. Complex 1 reacted with N₂O to give a mixture of two compounds, the bis­(diphenylamido) complex 6 and the doubly bridged μ-oxo complex 7. In contrast, reaction of 1 with 1 molar equiv of pyridinium N-oxide only gave the doubly bridged μ-oxo complex 7 along with 2,2′-bipyridine and diphenylamine.