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 Nα in a Cr-hydrazido complex. Our approach begins with the oxidation of chromium(IV) hydrazido precursor 1 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 2. Sequential ligand metathesis of 2 with aryl Grignard reagents (ArMgBr, Ar = biphenyl, p-methylphenyl, o-methoxyphenyl), alkenyl or alkyl Grignard reagents (1-phenylvinylmagnesium bromide and isopropylmagnesium bromide), followed by ligand migration from the Cr center to the Nα atom and electrophilic trapping (MeOH, PhCH2Br), affords structurally diverse hydrazines (4a-c, 5a-c, and 6). 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.