Mononuclear Five- and Six-Coordinate Iron Hydrazido and Hydrazine Species

This article describes the synthesis and characterization of several low-spin iron­(II) complexes that coordinate hydrazine (N2H4), hydrazido (N2H3–), and ammonia. The sterically encumbered tris­(di-meta-terphenylphosphino)­borate ligand, [PhBPmter3]−, is introduced to provide access to species that cannot be stabilized with the [PhBPPh3]− ligand ([PhBPR3]− = PhB­(CH2PR2)3–). Treatment of [PhBPmter3]­FeMe with hydrazine generates the unusual 5-coordinate hydrazido complex [PhBPmter 3]­Fe­(η2-N2H3) (1), in which the hydrazido serves as an L2X-type ligand. Upon coordination of an L-type ligand, the hydrazido shifts to an LX-type ligand, generating [PhBPmter3]­Fe­(L)­(η2-N2H3) (L = N2H4 (2) or NH3 (3)). In contrast, treatment of [PhBPPh3]­FeMe with hydrazine forms the adduct [PhBPPh3]­Fe­(Me)­(η2-N2H4) (5). Complex 5 is thermally unstable to methane loss, generating intermediate [PhBPPh3]­Fe­(η2-N2H3), which undergoes bimolecular coupling to produce {[PhBPPh3]­Fe}2(μ-η1:η1-N2H4)­(μ-η2:η2-N2H2). The oxidation of these and related hydrazine and hydrazido species is also presented. For example, oxidation of 1 or 5 with Pb­(OAc)4 results in disproportionation of the N2Hx ligand (x = 3, 4), and formation of [PhBPR3]­Fe­(NH3)­(OAc) (R = Ph (9) and mter (11)).