Mononuclear iron(III) complexes derived from tridentate ligands containing non-innocent phenolato donors: Self-activated nuclease, protease, and phenoxazinone synthase activity studies

The tridentate ligands (H)PhimpH, (OCH3)PhimpH, (CH3)PhimpH, (tBu)PhimpH, and (NO2)PhimpH have been synthesized and characterized. These tridentate ligands having non-innocent phenolato function, N-py and N-im donors upon deprotonation bind to iron(III) center resulting in a series of novel iron complexes, namely, [Fe((H)Phimp)(2)](ClO4) (1), [Fe((OCH3)Phimp)(2)](ClO4) (2), [Fe((CH3)Phimp)(2)](ClO4) (3), [Fe((tBu)Phimp)(2)](ClO4) (4), and [Fe((NO2)Phimp)(2)](ClO4) (5). Complexes were characterized by elemental analysis, IR, and UV-visible, and electrospray ionization mass spectral (ESI-MS) studies. Molecular structure of complex 2 was determined by single-crystal X-ray diffraction study. Electrochemical studies depicted Fe(III)/Fe(II) couple in the range of -0.50 to -0.65 V versus Ag/AgCl. Theoretical calculation using density functional theory (DFT) was also performed to optimize the geometrical and structural parameters. Time-dependent DFT (TD-DFT) was also optimized to observe the electronic properties, and data obtained were found to be consistent with experimentally observed values. Representative complex 4 exhibited nuclease and protease activities in the absence of external agents. Complex 4 was found to cleave the DNA and protein via self-activated mechanism. Complexes 1-5 were utilized to optimize oxidation of o-aminophenol in methanol. Complexes were found to be efficient in the oxidation of o-aminophenol. Kinetic experiments were also explored to gain better insight into the oxidation process.