Accessing iron amides from dimesityliron

•A new crystallographically characterized phase of mesityliron.•Rare high spin Fe-amido complexes characterized.•Topologically unique dpa− complexes without the usual M(II)–M(II) bonds.•EMAC structures typical for complexes of dpa− with M2+ are not found.

A new phase of dimesityliron has been crystallized from diethylether; the crystal structure shows a dinuclear complex with co-crystallized solvent. Crystalline [Fe2(mes)2(μ2-mes)2]·Et2O is a convenient starting material and reacts with di(2-pyridyl)amine to yield rare iron di(2-pyridyl)amido complexes. Crystal structures of air-sensitive [Fe2(mes)2(dpa)2], [Fe2(dpa)3Cl] and [Fe4(dpa)6O] were determined. [Fe4(dpa)6O] is known, and the dinuclear complexes [Fe2(mes)2(dpa)2] and [Fe2(dpa)3Cl] represent only the second and third reports of homometallic iron dpa− complexes. Long Fe … Fe distances of 3.043(1) and 3.104(2) Å in [Fe2(mes)2(dpa)2] and [Fe2(dpa)3Cl], respectively, and very unsymmetrically coordinated amido groups, indicate that the iron atoms are not involved in M–M bonding. This fact, and the relatively low coordination numbers of the high spin Fe(II) atoms are consistent with sensitivity of these compounds towards O2. DFT calculations were employed to rationalize the formation of the unusual architectures displayed by the dpa− complexes of iron.

Graphical abstractIron(II) complexes of di(2-pyridyl)amide (dpa−) prepared using mesityliron show unconventional structures and metal: ligand stoichiometries compared to the linear M–M bonded structures prolifically seen for this prototype ligand. Low coordination numbers and high-spin states for the iron rationalize their O2 sensitivity.Figure optionsDownload full-size imageDownload as PowerPoint slide