Iron 10‐Thiacorroles: Bioinspired Iron(III) Complexes with an Intermediate Spin (S=3/2) Ground State

Abstract

A first systematic study upon the preparation and exploration of a series of iron 10-thiacorroles with simple halogenido (F, Cl, Br, I), pseudo-halogenido (N3 , I3 ) and solvent-derived axial ligands (DMSO, pyridine) is reported. The compounds were prepared from the free-base octaethyl-10-thiacorrole by iron insertion and subsequent ligand-exchange reactions. The small N4 cavity of the ring-contracted porphyrinoid results in an intermediate spin (i.s., S=3/2) state as the ground state for the iron(III) ion. In most of the investigated cases, the i.s. state is found unperturbed and independent of temperature, as determined by a combination of X-ray crystallography and magnetometry with (1) H NMR-, EPR-, and Mössbauer spectroscopy. Two exceptions were found. The fluorido iron(III) complex is inhomogenous in the solid and contains a thermal i.s. (S=3/2)→high spin (h.s., S=5/2) crossover fraction. On the other side, the cationic bis(pyridine) complex resides in the expected low spin (l.s., S=1/2) state. Chemically, the iron 10-thiacorroles differ from the iron porphyrins mainly by weaker axial ligand binding and by a cathodic shift of the redox potentials. These features make the 10-thiacorroles interesting ligands for future research on biomimetic catalysts and model systems for unusual heme protein active sites.

Can Cyclen Bind Alkali Metal Azides? A DFT Study as a Precursor to Synthesis

“…The N 3 ‐side‐on structures M‐2 a (M=Li, Na, Rb) and M‐2 b (M=K, Cs) are similar to some crystal structures of transition metal azide‐NNNN containing macrocycles –,,. The N 3 unit of these structures adopts a side‐on conformation similar to that in the transition‐metal tetraaza analogues.…”

“…The N 3 unit of these structures adopts a side‐on conformation similar to that in the transition‐metal tetraaza analogues. However, the M−N−N bond angle is larger in these transition‐metal azides with M−N−N bond angles ranging from 121.3(2) ° to 149.7(8) ° for M=Co, Fe, Cu, Cr, Mn and Ru,–,, compared with 101.6–85.6 ° (BP86; B3LYP, 104.2–86.9 °) for the alkali metal N 3 ‐side‐on structures investigated in this work (Supporting Information, Tables S3 and S4). Several transition‐metal azide crystal structures– have the cyclam unit (1,4,8,11‐tetraazacyclotetradecane) as the macrocycle, which has four N−H groups as potential coordinating groups.…”

“…In these investigations, it was found that the azide ligand takes up an axial position on the transition metal macrocycle through strong interaction between the transition metal and the terminal N of the azide . Some of these complexes have been used in simple experiments that mimic the reactions of naturally occurring metalloenzymes, in which the azide group was mainly employed in ligand exchange reactions at the active sites ,,. The dissociative pathways of the photolabile azide ligand have also been highlighted in several reports ––.…”

Anorganische Chemie 2014

“…Dabei sind die jeweiligen Oxidations‐ und Spinzustände des zentralen Eisenions oft ein Schlüssel zum Verständnis der Proteinfunktion. Nach Einbau von Schwefel in einen heterocyclischen Corrol‐Liganden entwickelte die Arbeitsgruppe Bröring in Braunschweig eine Syntheseroute für Eisen(III)‐Komplexe mit 10‐Thiacorrol, einem kontrahierten Verwandten des natürlichen Porphyrinsystems 3_6. Als Folge der verkleinerten Kavität befindet sich das fünffach koordinierte Fe3+‐Ion hier deutlich oberhalb der Ringebene (Abbildung 3, oben).…”

Demetalation of copper undecaarylcorroles: Molecular structures of a free-base undecaarylisocorrole and a gold undecaarylcorrole

“…19 A second remarkable feature of isocorroles is their strong absorption in the near-infrared, [ 17 ] which is of great relevance to photodynamic therapy. 20 Reported herein are optimized syntheses for a family of sterically hindered undecaarylisocorrole ligands, including the first, single-crystal X-ray structure of a freebase undecaarylisocorrole.…”