title: Complete Series of {FeNO}(8), {FeNO}(7), and {FeNO}(6) Complexes Stabilized by a Tetracarbene Macrocycle.
abstract: Use of a macrocyclic tetracarbene ligand, which is topologically reminiscent of tetrapyrrole macrocycles though electronically distinct, has allowed for the isolation, X-ray crystallographic characterization and comprehensive spectroscopic investigation of a complete set of {FeNO}(x) complexes (x = 6, 7, 8). Electrochemical reduction, or chemical reduction with CoCp2, of the {FeNO}(7) complex 1 leads to the organometallic {FeNO}(8) species 2. Its crystallographic structure determination is the first for a nonheme iron nitroxyl {FeNO}(8) and has allowed to identify structural trends among the series of {FeNO}(x) complexes. Combined experimental data including (57)Fe Mössbauer, IR, UV-vis-NIR, NMR and Kβ X-ray emission spectroscopies in concert with DFT calculations suggest a largely metal centered reduction of 1 to form the low spin (S = 0) {FeNO}(8) species 2. The very strong σ-donor character of the tetracarbene ligand imparts unusual properties and spectroscopic signatures such as low (57)Fe Mössbauer isomer shifts and linear Fe-N-O units with high IR stretching frequencies for the NO ligand. The observed metal-centered reduction leads to distinct reactivity patterns of the {FeNO}(8) species. In contrast to literature reported {FeNO}(8) complexes, 2 does not undergo NO protonation under strictly anaerobic conditions. Only in the presence of both dioxygen and protons is rapid and clean oxidation to the {FeNO}(7) complex 1 observed. While 1 is stable toward dioxygen, its reaction with dioxygen under NO atmosphere forms the {FeNO}(6)(ONO) complex 3 that features an unusual O-nitrito ligand trans to the NO. 3 is a rare example of a nonheme octahedral {FeNO}(6) complex. Its electrochemical or chemical reduction triggers dissociation of the O-nitrito ligand and sequential formation of the {FeNO}(7) and {FeNO}(8) compounds 1 and 2. A consistent electronic structure picture has been derived for these unique organometallic variants of the key bioinorganic {FeNO}(x) functional units.
authors.affiliation: Institut für Anorganische Chemie, Georg-August-Universität , Tammannstrasse 4, D-37077 Göttingen, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Kupper
authors.affiliation: Max Planck Institute for Chemical Energy Conversion , Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany.|Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195-1700, United States.
authors.forename: Julian A
authors.initials: JA
authors.lastname: Rees
authors.affiliation: Institut für Anorganische Chemie, Georg-August-Universität , Tammannstrasse 4, D-37077 Göttingen, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Dechert
authors.affiliation: Max Planck Institute for Chemical Energy Conversion , Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany.|Department of Chemistry and Biochemistry, Cornell University , Ithaca, New York 14853, United States.
authors.forename: Serena
authors.initials: S
authors.lastname: DeBeer
authors.affiliation: Institut für Anorganische Chemie, Georg-August-Universität , Tammannstrasse 4, D-37077 Göttingen, Germany.
authors.forename: Franc
authors.initials: F
authors.lastname: Meyer