A dinucleating ligand system with varying terminal donor functions but without bridging donor functions: Design, synthesis, and applications for diiron complexes

A Dinucleating Ligand System with Varying Terminal Donors to Mimic Diiron Active Sites

“…Due to their tripodal topology, both ligand compartments coordinate in a cis configuration but while the two terminal carboxylate donors of the ligand julia 4À are in a trans orientation, the two terminal pyridines of the ligand susan are in a cis orientation. [66] This wrapping of the ligand julia 4À causes an arrangement of the terminal H 2 O ligands with a dihedral angle (H 2 OÀ FeÀ FeÀ H 2 O) of 59°. On the other hand, the two terminal Cl À donors in [(susan){FeCl(μ-O)FeCl}] 2 + are trans relative to the central Fe-μ-OÀ Fe core resulting in a dihedral angle of 170°.…”

“…We studied the μ-oxo-bridged diiron complexes intensively by magnetic, electrochemical, and spectroscopic means. [45,66,[69][70][71] It turned out, that the UV-Vis-NIR spectroscopic and magnetic properties are only slightly depending on the nature of the anionic ligand X À in the mono-μ-oxo-bridged complexes [(susan){Fe III X(μ-O)Fe III X}] 2 + . [66] However, the variation of the bridging mode from mono-bridged μ-oxo to doublybridged μ-oxo,μ-carboxylato results in strong differences in the UV-Vis-NIR spectra, which is known from tpa-based complexes.…”

“…[45,66,[69][70][71] It turned out, that the UV-Vis-NIR spectroscopic and magnetic properties are only slightly depending on the nature of the anionic ligand X À in the mono-μ-oxo-bridged complexes [(susan){Fe III X(μ-O)Fe III X}] 2 + . [66] However, the variation of the bridging mode from mono-bridged μ-oxo to doublybridged μ-oxo,μ-carboxylato results in strong differences in the UV-Vis-NIR spectra, which is known from tpa-based complexes. [84][85][86] Figure 5 shows a comparison of the UV-Vis-NIR spectra of the mono-[(susan){Fe(OAc)(μ-O)Fe(OAc)}] 2 + and doubly-bridged [(susan){Fe(μ-O)(μ-OAc)Fe}] 3 + complexes.…”

Dinuclear Diferrous Complexes of a Bis(tetradentate) Dinucleating Ligand: Influence of the Exogenous Ligands on the Molecular and Electronic Structures

“…In order to further explore the geometric and electronic structures and their relation to reactivity, we have developed a dinucleating ligand system consisting of two ethylene-bridged tripodal ligand compartments with varying terminal donors. [15,16] The ligand H 4 julia (Scheme 1) was used to realize a {Fe III (μ-O) 2 Fe III } core in aqueous solution which is oxidized at room temperature by atmospheric O 2 to a transient Fe III Fe IV intermediate. [17] Oxo-bridged diferric complexes of susan catalyze the hydroxylation of cyclohexane in the presence of organic peroxides, [18] and the oxidation of methanol with H 2 O 2 to formaldehyde, formate, and CO 2 .…”

“…[19] Although the peroxo intermediate [(susan){Fe III (μ-O 2 )(μ-O)Fe III }] 2 + is not the active species, it is too reactive to be isolated or further characterized under these catalytic conditions. [19] Despite the straightforward syntheses of mono-bridged μoxo diferric complexes [(susan){Fe III X(μ-O)Fe III X}] 2 + (X=Cl À , F À , OAc À , OMe À , OH À ) [15,16,18,[20][21][22] and doubly-bridged complexes [(susan){Fe III (μ-O)(μ-OAc)Fe III }] 3 + , [21] [(susan){Fe III (μ-O)(μ-O 2 CH)Fe III }] 3 + , [19] and [(susan){Fe III (μ-O)(μ-CO 3 )Fe III }] 3 + , [23] such complexes are not accessible with the ligand susan 6À Me (Scheme 1). [22] An exception is the complex [(susan 6À Me ){Fe III F(μ-O)Fe III F}](ClO 4 ) 2 with the small ligand F À that could be obtained only under much harsher conditions than for the susan complexes.…”