title: Iron(II) vacataporphyrins: a variable annulene conformation inside a regular porphyrin frame.
abstract: 5,10,15,20-Tetraaryl-21-vacataporphyrin (1), an annulene-porphyrin hybrid containing a butadiene fragment in the macrocycle perimeter, gives paramagnetic iron(II) complexes 2. The porphyrin 1 is devoid of one donor atom of the coordination core; hence, metal ion is bound in the macrocyclic cavity by only three pyrrolic nitrogen atoms. The coordination sphere in 2-X (where X = Cl, Br, I) is completed by a halide anion. The butadiene fragment flexibility and constraints of coordination lead to two stereoisomers with the chain oriented inward (2-i-X) or outward (2-o-X) of the macrocyclic center. Axial halide subtraction (AgBF(4) addition) leads to two new forms differing in the butadiene chain configuration. The (1)H NMR spectra of all complexes show characteristics typical for high-spin iron(II) complexes of porphyrinoids. The dependence of the relaxation times T(1) versus Fe(II)···H distances (estimated by MM+ models) for three of the isomers is in accordance with the in, out, and/or zigzag geometries. The 2-o-X complex is more reactive than 2-i-X and reacts at room temperature with dioxygen to form the iron(II) 21-oxaporphyrin complex, conserving the iron(II) oxidation state. After the addition of imidazole or excess of methanol to a mixture of 2-o-X and 2-i-X, single five-coordinate complexes with out annulene configuration and two axial ligands are formed.
authors.affiliation: Department of Chemistry, University of Wrocław, ul. F. Joliot-Curie 14, 50-383 Wrocław, Poland. ewa.dudziak@chem.uni.wroc.pl
authors.forename: Ewa
authors.initials: E
authors.lastname: Pacholska-Dudziak
authors.forename: Aneta
authors.initials: A
authors.lastname: Gaworek
authors.forename: Lechosław
authors.initials: L
authors.lastname: Latos-Grażyński
mesh_terms: D002070:Butadienes / Q000737:chemistry; D015393:Chemistry, Bioinorganic / Q000379:methods*; D056831:Coordination Complexes / Q000032:analysis / Q000138:chemical synthesis*; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D005296:Ferrous Compounds / Q000032:analysis / Q000138:chemical synthesis*; D006219:Halogens / Q000737:chemistry; D007093:Imidazoles / Q000737:chemistry; D007501:Iron / Q000737:chemistry / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008280:Magnetics; D008665:Metalloporphyrins / Q000032:analysis / Q000138:chemical synthesis*; D008958:Models, Molecular; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D011166:Porphyrins / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D002070:Butadienes; D056831:Coordination Complexes; D005296:Ferrous Compounds; D006219:Halogens; D007093:Imidazoles; D008665:Metalloporphyrins; D011166:Porphyrins; D007501:Iron