Mechanism of the interaction of Mn tetraazaporphines with peracetic acid -The comparative reactivity of Mn(III) porphinoid complexes in the formation of Mn-oxenes

The mechanism of peracetic acid interaction with Mn(III) complexes of tetra -R-tetra-tert-butyl-tetraazaporphines (RTAPM-nCl, R = H, Br, PhSO2, NO2) in acetonotrile/acetic acid solutions has been studied. Analysis of the kinet ic data of trans-stilbene epoxidation, naphthalene hydroxylation, 1, 1 -dip henyl-2-picrylhydrazine (DPPH), and tetra-4-tert-butyl-phthalocyanine zinc (PcZn) one-electron oxidations revealed the reversible formation of a two-c enter molecular "catalyst-oxidant" complex ligated with a molecule of aceti c acid { A = [RTAPMn(AcOOH)(AcOH)] (X)}. The subsequent irreversible transf ormation of A with rate constant k(2) leads to the formation of two high-va lent oxometallo species, supposedly [RTAPMn(V)(O)(AcOH)](X) and [(.+)RTAPMn (IV)(O)(AcOH)](X), which are in equilibrium and show distinct oxidation abi lities towards olefin and naphthalene. The Hammett-type dependencies of k2 and of the rate constant of A formation (kj) have been analyzed and compare d with those ones determined earlier for Mn(III) meso-tetra(2,6-dichloro-4- R-phenyl)porphyrins (RTDCPPM-nCl). The enhanced sensibility of the acceptor properties of Mn ion to electronegative substitution in tetraazaporphine m acrocycle is considered to be a reason of the highest catalytic oxidative a ctivity of Mn-tetra-nitro-tetra-tert-butyltetraazaporphine within studied M n porphinoids. (C) 2001 Elsevier Science B.V. All rights reserved.