Metallkomplexe mit Tetrapyrrol-Liganden, XIX [1]. Synthese und elektrochemische Charakterisierung der Kohlenmonosulfid-Metalloctaethylporphyrine mit Eisen(II) oder Osmium(II) im Zentrum. Ein Beitrag zur "Bathochromie-Regel" / Metal Complexes with Tetrapyrrole Ligands, XIX [1]. Synthesis and Electrochemical Characterization of Thiocarbonyl Metallooctaethylporphyrins with Iron(II) or Osmium(II) in the Center. A Contribution to the "Rule of Bathochromism"

Abstract

The preparation and spectroscopic characterization of thiocarbonyl metalloporphyrins M(OEP)CS(L') (e.g. 2e: M = Fe, L' = Py, 1e: M = Os, L' = Py** are described. Especially noteworthy is the existence of a pentacoordinate, diamagnetic, air-stable heme Fe(OEP)CS (2f: M = Fe, no L′). A linear correlation of the α-band frequencies (expressed as ϋ_a) in the optical spectrum and the metal(II/III) redox potentials (E_1/2) taken from cyclic voltam­metry experiments suggests (Abb. 3) that in complexes of the type M(OEP)LL' (1,2) λ_a is bathochromically shifted as the π-acceptor capacity of L increases (“Rule of Bathochromism”). The strong π-acceptor capacity of carbon monosulphide renders the attack of dioxygen to the thiocarbonyl heme unfavourable; O₂ and CS seem to be comparable in their π-acceptor strength.