title: Synthesis and characterization of divalent manganese, iron, and cobalt complexes in tripodal phenolate/N-heterocyclic carbene ligand environments.
abstract: Two novel tripodal ligands, (BIMPN(Mes,Ad,Me))(-) and (MIMPN(Mes,Ad,Me))(2-), combining two types of donor atoms, namely, NHC and phenolate donors, were synthesized to complete the series of N-anchored ligands, ranging from chelating species with tris(carbene) to tris(phenolate) chelating arms. The complete ligand series offers a convenient way of tuning the electronic and steric environment around the metal center, thus, allowing for control of the complex's reactivity. This series of divalent complexes of Mn, Fe, and Co was synthesized and characterized by (1)H NMR, IR, and UV/vis spectroscopy as well as by single-crystal X-ray diffraction studies. Variable-temperature SQUID magnetization measurements in the range from 2 to 300 K confirmed high-spin ground states for all divalent complexes and revealed a trend of increasing zero-field splitting |D| from Mn(II), to Fe(II), to Co(II) complexes. Zero-field (57)Fe Mössbauer spectroscopy of the Fe(II) complexes 3, 4, 8, and 11 shows isomer shifts δ that increase gradually as carbenes are substituted for phenolates in the series of ligands. From the single-crystal structure determinations of the complexes, the different steric demand of the ligands is evident. Particularly, the molecular structure of 1-in which a pyridine molecule is situated next to the Mn-Cl bond-and those of azide complexes 2, 4, and 6 demonstrate the flexibility of these mixed-ligand derivatives, which, in contrast to the corresponding symmetrical TIMEN(R) ligands, allow for side access of, e.g., organic substrates, to the reactive metal center.
authors.affiliation: Department of Chemistry and Pharmacy, Inorganic Chemistry, Friedrich-Alexander-University Erlangen-Nuremberg , Egerlandstrasse 1, 91058 Erlangen, Germany.
authors.forename: Martina
authors.initials: M
authors.lastname: Käß
authors.forename: Johannes
authors.initials: J
authors.lastname: Hohenberger
authors.forename: Mario
authors.initials: M
authors.lastname: Adelhardt
authors.forename: Eva M
authors.initials: EM
authors.lastname: Zolnhofer
authors.forename: Susanne
authors.initials: S
authors.lastname: Mossin
authors.forename: Frank W
authors.initials: FW
authors.lastname: Heinemann
authors.forename: Jörg
authors.initials: J
authors.lastname: Sutter
authors.forename: Karsten
authors.initials: K
authors.lastname: Meyer