Diazene-N-(di-imide) and hydrazido-(2–)N-(aminoimido) complexes: the addition of acids to dinitrogen complexes

Abstract

The protonation and reduction of dinitrogen in a mononuclear complex are described. The diazene compounds [MX₂(N₂H₂)(dpe)₂](I; M = W, X = Cl or Br; M = MO, X = Br; dpe = Ph₂PCH₂CH₂PPh₂), and hydrazido (2–)N complex salts, [Mo(N₂H₂)(depe)₂]X (X = Cl or Br; depe = Et₂PCH₂CH₂PEt₂) and trans-[WCl(N₂H₂)(PMe₂Ph)₄]Cl were prepared by the reaction of trans-[M(N₂)₂(diphos)₂](M = MO or W; diphos = dpe or depe) or cis-[W(N₂)₂(PMe₂Ph)₄] with an excess of the appropriate hydrogen halide. Compounds (I) contain labile halogen and are converted into the hydrazido-(2–)N complex salts [MX(N₂H₂)(dpe)₂]Y (Y = BPh₄, ClO₄, or PF₆, M = W; Y = BF₄, M = MO) by treatment with NaBPh₄, LiClO₄, NaPF₆, or [NEt₄]BF₄ as appropriate. The structural implications of the i.r., ¹H and ³¹P n.m.r. spectroscopic properties of the N₂H₂ compounds and of their ¹⁵N analogues are discussed.

With only 2 mol equiv. of HCl, trans-[W(N₂)₂(dpe)₂] gives the hydride [WH(N₂)₂(dpe)₂]HCl₂ and trans-[Mo(N₂)₂(dpe)₂] gives the dihydride [MoH₂Cl₂(dpe)₂]. [WH(N₂)₂(dpe)₂]HCl₂ is converted into [WH₂Cl₂(dpe)₂] in refluxing methanol and [WCl₂(N₂H₂)(dpe)₂] gives [WCl₂{N₂H(COCH₃)}(dpe)₂] with acetyl chloride or acetic anhydride.

This work provides the first chemical evidence that dinitrogen is as likely to be reduced at a mono- as at a bi-metal site in nitrogenase.