Harnessing Chromium(V) Hydrazido Intermediates for N₂ Functionalization to Multisubstituted Hydrazines through Ligand Migration

The direct conversion of N₂ into N-containing organic compounds remains a fundamental challenge in synthetic chemistry. Here, we report a high-valent chromium(V)-mediated strategy for synthesizing multisubstituted hydrazine derivatives via ligand migration, representing ligand migration to N_α in a Cr-hydrazido complex. Our approach begins with the oxidation of chromium(IV) hydrazido precursor <b>1</b> by benzyl bromide, which replaces the 1,2-bis(diethylphosphino)ethane (depe) ligand with two bromide ions to generate the high-valent chromium(V) dibromide hydrazido complex <b>2</b>. Sequential ligand metathesis of <b>2</b> with aryl Grignard reagents (ArMgBr, Ar = biphenyl, <i>p</i>-methylphenyl, <i>o</i>-methoxyphenyl), alkenyl or alkyl Grignard reagents (1-phenylvinylmagnesium bromide and isopropylmagnesium bromide), followed by ligand migration from the Cr center to the N_α atom and electrophilic trapping (MeOH, PhCH₂Br), affords structurally diverse hydrazines (<b>4a-c</b>, <b>5a-c</b>, and <b>6</b>). Single-crystal X-ray crystallography, in situ UV-vis spectroscopy, and DFT calculations collectively reveal a ligand migration mechanism in chromium chemistry, directly forging N-C bonds from N₂ without ammonia intermediates. This migration not only constructs new N-C bonds but also enables the direct construction of complex hydrazine structures directly from N₂.