Substrate-dependent aromatic ring fission of catechol and 2-aminophenol with O₂ catalyzed by a nonheme iron complex of a tripodal N₄ ligand

The catalytic reactivity of an iron(ii) complex [(TPA)Fe^II(CH₃CN)₂]²⁺ (1) (TPA = tris(2-pyridylmethyl)amine) towards oxygenative aromatic C-C bond cleavage of catechol and 2-aminophenol is presented. Complex 1 exhibits catalytic and regioselective C-C bond cleavage of 3,5-di-tert-butylcatechol (H₂DBC) to form intradiol products, whereas it catalyzes extradiol-type C-C bond cleavage of 2-amino-4,6-di-tert-butylphenol (H₂AP). The catalytic reactions are found to be pH-dependent and the complex exhibits maximum turnovers at pH 5 in acetonitrile-phthalate buffer. An iron(iii)-catecholate complex [(TPA)Fe^III(DBC)]⁺ (2) is formed in the ring cleavage of catechol. In the extradiol-type cleavage of H₂AP, an iron(iii)-2-iminobenzosemiquinonate complex [(TPA)Fe^III(ISQ)]²⁺ (3) (ISQ = 4,6-di-tert-butyl-2-iminobenzosemiquinonate radical anion) is observed in the reaction pathway. This work shows the importance of the nature of 'redox non-innocent' substrates in governing the mode of ring fission reactivity.