Synthesis, Characterization, and the Effect of Lewis Bases on the Nuclearity of Iron Alkoxide Complexes

Inspired by the potential of alkoxides as weak-field ligands and their ability to bridge, we report herein a series of high-spin iron complexes supported by a bis-alkoxide framework ^PhDbf. A diiron complex [Fe₂(^PhDbf)₂] (1a) is obtained upon metalation of the ligand, whereas addition of substituted pyridines affords five-coordinate mononuclear iron complexes [(R-Py)₂Fe(^PhDbf)] (2a-4a, R = H, p-^tBu, p-CF₃). The potential for nuclearity control of the metal complexes via auxiliary ligands is highlighted by the formation of asymmetric diiron species [(p-CF₃-Py)Fe₂(^PhDbf)₂] (5a) and [(m-CF₃-Py)Fe₂(^PhDbf)₂] (6a) with trifluoromethyl substituted pyridines, while electron-rich pyridines only produced monomeric species. Electronic properties analysis via UV-vis, electron paramagnetic resonance, ⁵⁷Fe Mössbauer spectroscopy, and time-dependent density functional theory, along with redox capabilities of these complexes are reported to illustrate the effect of nuclearity on reactivity and the potential of these complexes to access higher oxidation states relevant in oxidative chemistry. Species 1a-5a, [(THF)₂Fe(^PhDbf)][PF₆] (7), [PyFe(^PhDbf)Cl] (2b), and [Py₂Fe(^PhDbf)][PF₆] (2c) were characterized via SCXRD. Indirect evidence for the formation of dimeric Fe(III) species (1b, 5b, and 6b) is discussed.