Biomedical subjects
Publications and source records attributed to Liliya Simkhovich.
The first full assignment of (1)H NMR chemical shifts for iron corroles and the first synthesis of a series of (halogeno)iron corroles reveal very large effects of the axial ligands on the corresponding spectra, which apparently reflect differences in the relative importance of metal-to-corrole and corrole-to-metal pi-donation. These findings pave the way for a thorough analysis of the electronic structures of such complexes.
[reaction: see text] Following the discovery that meso-substituted corroles are formed in solvent-free condensation of pyrrole with aldehydes, we demonstrate that a small variation in the methodology is suitable for facile synthesis of cobalt(III) corrole and hexaphyrin. These compounds, as well as three noncyclic products, were fully characterized by spectroscopy and X-ray crystallography.
The aim of this research was to prepare mononuclear ruthenium corroles, because of the well-documented potency of analogous porphyrin complexes in catalysis. The syntheses of the mononuclear nitrosyl complexes [Ru(tpfc)(NO)] and [Ru(tdcc)(NO)] (tpfc=trianion of 5,10,15-tris(pentafluorophenyl)corrole, tdcc=trianion of 5,10,15-tris(2,6-dichlorophenyl)corrole), and of the binuclear [[Ru(tpfc)](2)] were achieved by using [[Ru(cod)Cl(2)](x)] (cod=cyclooctadiene) as the metal source. The NMR spectra of all three complexes clearly demonstrate that they are diamagnetic; this is consistent with a triple bond between the metal ions in [[Ru(tpfc)](2)] and is expected for classical [MNO](6) complexes. These features were further substantiated by the stretching frequencies of the [MNO] moieties, electrochemical measurements on all complexes, and the X-ray crystal structures of [Ru(tpfc)(NO)] and [[Ru(tpfc)](2)]. A comparison of the spectroscopic and structural characteristics of these new complexes with analogous iron corroles, as well as with iron and ruthenium porphyrins, suggests that it will be hard to obtain mononuclear ruthenium corroles without pi-accepting ligands.
A delicate control of reaction conditions allows the isolation of several distinctively different iron complexes of tris(pentafluorophenyl)- and tris(2,6-dichlorophenyl)corrole. As long as coordinating ligands are present, the iron(III) complexes are stable in solution. Otherwise they are aerobically oxidized to either mononuclear chloroiron(IV) or dinuclear (mu-oxo)iron(IV) complexes, in acidic and basic solutions, respectively (the latter holds only for tris(pentafluorophenyl)corrole). When treated with NaNO(2), the mononuclear chloroiron(IV) corroles are efficiently converted into diamagnetic iron nitrosyl complexes. The low- and intermediate-spin iron(III), iron nitrosyl, and chloroiron(IV) corroles were fully characterized by a combination of spectroscopic methods and X-ray crystallography. There was no indication for an open-shell corrole in any of the complexes.
In the present work we report on the detailed structural features of the chiral N21- and N22-substituted benzyl and picolyl derivatives of tris(pentafluorophenyl)corrole [H3(tpfc)]. The main difference between the isomers is that substitution on N22 creates a much more crowded environment, reflected in higher deformation of the corrole ring from planarity and of the meso-aryls from perpendicular orientation. The effects of metal-ion chelation on corrole geometry are demonstrated by structural investigations of the zinc(II) and rhodium(I) complexes of the N21- and N22-alkylated corroles. The major finding is the intramolecular coordination of the pyridine moiety of the picolyl substituent in the case of [ZnII(N21-picolyl-tpfc)]. This pyridine is readily attracted to the zinc ion as an axial ligand, thus replacing the external pyridine molecule of the precursor [ZnII(N21-benzyl-tpfc)(py)]. The change is associated with a considerable flattening of the corrole ring in order to allow a more convenient coordination of the zinc ion to all four pyrrole nitrogen atoms (at Zn-N(pyr-role) distances of 1.956-1.987 A for the nonsubstituted sites, and 2.224-2.247 A for the substituted sites). These structural investigations also aid a good understanding of the spectroscopic characteristics of the derivatives.