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

Abstract

The N–N bond in the zirconium hydrazinediido(2−) complex [Zr­(N₂^TBSN_py)­(NNPh₂)­(py)] (<b>1</b>) is readily cleaved by one-electron oxidation. Reacting [Zr­(N₂^TBSN_py)­(NNPh₂)­(py)] (<b>1</b>) 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)] (<b>2</b>). Exposure of hydrazinediide <b>1</b> to an excess of iodine resulted in further oxidation of the diphenylamido ligand, yielding the diiodo complex <b>3</b> and tetraphenylhydrazine. Similar reactivity was observed in the reaction of <b>1</b> with diphenyl diselenide and diaryl disulfides, which reacted to give the corresponding diphenylamido/arylchalcogenido complexes [Zr­(N₂^TBSN_pyNPh₂)­(SePh)] (<b>4a</b>) and [Zr­(N₂^TBSN_py)­(NPh₂)­(SAr)] (Ar = Ph (<b>4b</b>), C₆F₅ (<b>4c</b>)) along with N₂. The reactions were also carried out on an NMR scale with a ¹⁵N_α-labeled hydrazido complex (<b>1-</b>^<b>15</b><b>N</b>). 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 <b>1</b> and ¹⁵N_α-labeled <b>1-</b>^<b>15</b><b>N</b> 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 <b>1</b> reacted with N₂O to give a mixture of two compounds, the bis­(diphenylamido) complex <b>6</b> and the doubly bridged μ-oxo complex <b>7</b>. In contrast, reaction of <b>1</b> with 1 molar equiv of pyridinium <i>N</i>-oxide only gave the doubly bridged μ-oxo complex <b>7</b> along with 2,2′-bipyridine and diphenylamine