title: Design and synthesis of a dinucleating ligand system with varying terminal donor functions that provides no bridging donor and its application to the synthesis of a series of Fe(III)-μ-O-Fe(III) complexes.
abstract: Based on a rational ligand design for stabilizing high-valent {Fe(μ-O)2Fe} cores, a new family of dinucleating bis(tetradentate) ligands with varying terminal donor functions has been developed: redox-inert biomimetic carboxylates in H4julia, pyridines in susan, and phenolates in H4hilde(Me2). Based on a retrosynthetic analysis, the ligands were synthesized and used for the preparation of their diferric complexes [(julia){Fe(OH2)(μ-O)Fe(OH2)}]·6H2O, [(julia){Fe(OH2)(μ-O)Fe(OH2)}]·7H2O, [(julia){Fe(DMSO)(μ-O)Fe(DMSO)}]·3DMSO, [(hilde(Me2)){Fe(μ-O)Fe}]·CH2Cl2, [(hilde(Me2)){FeCl}2]·2CH2Cl2, [(susan){FeCl(μ-O)FeCl}]Cl2·2H2O, [(susan){FeCl(μ-O)FeCl0.75(OCH3)0.25}](ClO4)2·0.5MeOH, and [(susan){FeCl(μ-O)FeCl}](ClO4)2·0.5EtOH, which were characterized by single-crystal X-ray diffraction, FTIR, UV-Vis-NIR, Mössbauer, magnetic, and electrochemical measurements. The strongly electron-donating phenolates afford five-coordination, while the carboxylates and pyridines lead to six-coordination. The analysis of the ligand conformations demonstrates a strong flexibility of the ligand backbone in the complexes. The different hydrogen-bonding in the secondary coordination sphere of [(julia){Fe(OH2)(μ-O)Fe(OH2)}] influences the C-O, C[double bond, length as m-dash]O, and Fe-O bond lengths and is reflected in the FTIR spectra. The physical properties of the central {Fe(μ-O)Fe} core (d-d, μ-oxo → Fe(III) CT, νas(Fe-O-Fe), J) are governed by the differences in terminal ligands - Fe(III) bonds: strongly covalent π-donation with phenolates, less covalent π-donation with carboxylates, and π-acceptation with pyridines. Thus, [(susan){FeCl(μ-O)FeCl}](2+) is oxidized at 1.48 V vs. Fc(+)/Fc, which is shifted to 1.14 V vs. Fc(+)/Fc by methanolate substitution, while [(julia){Fe(OH2)(μ-O)Fe(OH2)}] is oxidized ≤1 V vs. Fc(+)/Fc. [(hilde(Me2)){Fe(μ-O)Fe}] is oxidized at 0.36 V vs. Fc(+)/Fc to a phenoxyl radical. The catalytic oxidation of cyclohexane with TONs up to 39.5 and 27.0 for [(susan){FeCl(μ-O)FeCl}](2+) and [(hilde(Me2)){Fe(μ-O)Fe}], respectively, indicates the potential to form oxidizing intermediates.
authors.affiliation: Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie, Universität Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany. thorsten.glaser@uni-bielefeld.de.
authors.forename: Julia Bernhardette Hildegard
authors.initials: JB
authors.lastname: Strautmann
authors.affiliation: Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie, Universität Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany. thorsten.glaser@uni-bielefeld.de.
authors.forename: Susanne
authors.initials: S
authors.lastname: Dammers
authors.affiliation: Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie, Universität Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany. thorsten.glaser@uni-bielefeld.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Limpke
authors.affiliation: Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie, Universität Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany. thorsten.glaser@uni-bielefeld.de.
authors.forename: Janine
authors.initials: J
authors.lastname: Parthier
authors.affiliation: Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie, Universität Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany. thorsten.glaser@uni-bielefeld.de.
authors.forename: Thomas Philipp
authors.initials: TP
authors.lastname: Zimmermann
authors.affiliation: Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie, Universität Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany. thorsten.glaser@uni-bielefeld.de.
authors.forename: Stephan
authors.initials: S
authors.lastname: Walleck
authors.affiliation: Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie, Universität Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany. thorsten.glaser@uni-bielefeld.de.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Heinze-Brückner
authors.affiliation: Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie, Universität Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany. thorsten.glaser@uni-bielefeld.de.
authors.forename: Anja
authors.initials: A
authors.lastname: Stammler
authors.affiliation: Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie, Universität Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany. thorsten.glaser@uni-bielefeld.de.
authors.forename: Hartmut
authors.initials: H
authors.lastname: Bögge
authors.affiliation: Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie, Universität Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany. thorsten.glaser@uni-bielefeld.de.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Glaser