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, [PhBP3mter](-), is introduced to provide access to species that cannot be stabilized with the [PhBP3Ph](-) ligand ([PhBP3R](-) = PhB(CH2PR2)(3)(-)). Treatment of [PhBP3mter]FeMe with hydrazine generates the unusual 5-coordinate hydrazido complex [PhBP3mter]Fe(eta(2)-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 [PhBP3mter]Fe(L)(eta(2)-N2H3) (L = N2H4 (2) or NH3 (3)). In contrast, treatment of [PhBP3Ph]FeMe with hydrazine forms the adduct [PhBP3Ph]Fe(Me)(;eta(2)-N2H4) (5). Complex 5 is thermally unstable to methane loss, generating intermediate [PhBP3Ph]Fe(eta(2)-N2H3), which undergoes bimolecular coupling to produce {[PhBP3Ph]Fe}(2)(mu-eta(1):eta(1)-N2H4)(mu-eta(2):eta(2)-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 [PhBP3R]Fe(NH3)(OAc) (R = Ph (9) and mter (11)).