Iron carbonyl complexes of heterocyclic α-diimines: systematic synthesis, crystal structures of [Fe(CO)3(L)] and [Fe2(CO)7(L)] (L=2,2′-bipyridine and 1,10-phenantroline), and their AIM analysis

Heterocyclic α-diimines {2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (4,4′-Me2bpy), 1,10-phenantroline (phen), 4,7-dimethyl-1,10-phenantroline (4,7-Me2phen) and 2,9-dimethyl-1,10-phenantroline (2,9-Me2phen)} react, in a wide range of conditions, with iron clusters of nuclearity one, two or three. Two kinds of compounds, [Fe(CO)3(α-diimine)] (type 1) and [Fe2(CO)7(α-diimine)] (type 2), are afforded in all cases. We propose a reaction mechanism to explain this behaviour. The crystal structures of compounds [Fe(CO)3(bpy)] (1a), [Fe(CO)3(phen)] (1b), [Fe2(CO)7(bpy)] (2a) and [Fe2(CO)7(phen)] (2b) at 173 K were determined by single-crystal X-ray diffraction methods. In contrast, reaction of the pentanuclear iron cluster [Fe5C(CO)15] with bpy led to the tetranuclear salt [Fe(bpy)3][(μ-H)Fe4C(CO)12]2 (3). The electronic structures of the mono- and di-iron derivatives with bpy and phen were analysed using the atoms in molecules (AIM) theory. Their comparative study seems to rule out the existence of FeFe bond in the dinuclear complexes.