Abstract
A new end-on low-spin ferric heme peroxide, [(P(Im) )Fe(III) -(O(2)(2-) )](-) (P(Im) -P), and subsequently formed hydroperoxide species, [(P(Im) )Fe(III) -(OOH)] (P(Im) -HP) are generated utilizing the iron-porphyrinate P(Im) with its tethered axial base imidazolyl group. Measured thermodynamic parameters, the ferric heme superoxide [(P(Im) )Fe(III) -(O(2)(⋅-) )] (P(Im) -S) reduction potential (E°') and the P(Im) -HP pK(a) value, lead to the finding of the OO-H bond-dissociation free energy (BDFE) of P(Im) -HP as 69.5 kcal mol(-1) using a thermodynamic square scheme and Bordwell relationship. The results are validated by the observed oxidizing ability of P(Im) -S via hydrogen-atom transfer (HAT) compared to that of the F(8) superoxide complex, [(F(8) )Fe(III) -(O(2)(.-) )] (S) (F(8) =tetrakis(2,6-difluorophenyl)porphyrinate, without an internally appended axial base imidazolyl), as determined from reactivity comparison of superoxide complexes P(Im) -S and S with the hydroxylamine (O-H) substrates TEMPO-H and ABNO-H.