Spontaneous Reduction of Mononuclear High‐Spin Iron(III) Complexes to Mononuclear Low‐Spin Iron(II) Complexes in Aqueous Media and Nuclease Activity via Self‐Activation

Abstract

Mononuclear high-spin [Fe(III) (Pyimpy)Cl3 ]⋅2 CH2 Cl2 (1⋅2 CH2 Cl2 ) and [Fe(III) (Me-Pyimpy)Cl3 ] (2), as well as low-spin Fe(II) (Pyimpy)2 ](ClO4 )2 (3) and [Fe(II) (Me-Pyimpy)2 ](ClO4 )2 (4) complexes of tridentate ligands Pyimpy and Me-Pyimpy have been synthesized and characterized by analytical techniques, spectral, and X-ray structural analyses. We observed an important type of conversion and associated spontaneous reduction of mono-chelated high-spin Fe(III) (1⋅2 CH2 Cl2 and 2) complexes to low-spin bis-chelated Fe(II) complexes 3 and 4, respectively. This process has been explored in detail by UV/Vis, fluorescence, and (1) H NMR spectroscopic measurements. The high positive potentials observed in electrochemical studies suggested a better stabilization of Fe(II) centers in 3 and 4. Theoretical studies by density functional theory (DFT) calculations supported an increased stabilization for 3 in polar solvents. Self-activated nuclease activity of complexes 1⋅2CH2 Cl2 and 2 during their spontaneous reduction was examined for the first time and the mechanism of nuclease activity was investigated.

Oxidation chemistry of C–H bond by mononuclear iron complexes derived from tridentate ligands containing phenolato function

“…For complexes 1 to 4, magnetic moments were found to be 5.31, 5.49, 5.59, 5.85BM respectively, that is predicting the stabilization of high-spin d 5 iron(III) centre in all complexes, it is consistent with the magnetic moment reported in literature. [47] (See supporting information S14−S17). Thermal stability of all the complexes was determined using TGA analysis.…”

Selective oxidation of benzyl alcohol to benzaldehyde, 1‐phenylethanol to acetophenone and fluorene to fluorenol catalysed by iron (II) complexes supported by pincer‐type ligands: Studies on rapid degradation of organic dyes

“…The Fe–N im bond distances are 1.875 Å (Fe1—N3) and 1.912 Å Fe1—N7 and Fe–N py distances have been found to have slight differences 2.031 Å (Fe1—N8), 2.031 Å (Fe1‐N5), 2.093 Å (Fe1‐N4), 2.122 Å (Fe1‐N1). A similar pattern was observed in case of complex 2 (minor differences in N py distances) N py distances were found consistent with the data reported in the literature, however the N im distances were shorter in our case as compared to the reported values. The bond parameters for complexes 1 and 2 were quite similar to the data obtained from theoretically optimized geometries of both the complexes (shown in Table S8).…”

“…We have recently reported iron complex derived from meridional tridentate ligand (L Ph ) having NNN donors (Shown in Scheme ) . Addition of H 2 O 2 to this complex did not provide us the indication of generation of stable hydroperoxo and oxo species in solution.…”

“…Investigation of literature revealed that Borovik and co‐workers, Goldberg and co‐workers, and Fout and co‐workers reported the stabilization of Fe IV =O through hydrogen bonding because the hydrogen atom present in the ligand system showed proximity with the Fe IV =O species . We have performed theoretical (DFT and TD‐DFT) calculations for the complex derived from L Ph described in our previous report . (Shown in Figure S38) and we designed new ligands (L 1 and L 2 as shown in Scheme ) which possibly could stabilize hydroperoxo and oxo species through hydrogen bonding during catalytic activity.…”

Imidazolidine Ring Cleavage upon Complexation with First‐Row Transition Metals

“…Spontaneous reduction of the Fe III under aerobic conditions is quite rare in iron coordination chemistry. A few examples of the spontaneous reduction of a ferric ion chelated with bis(methylimidazolyl)ketone, salicyloyl hydrazonodithiolane, hydrazide, or Schiff base ligands have been identified in the literature, but the mechanism of the reduction has not been reported. Nevertheless, Sosa‐Torres et al reported that oxidative dehydrogenation of polyamine ligands in the presence of Fe III led to the Fe II complexes of the corresponding imine ligands , .…”