REACTION OF HYDROXIDE ION WITH MANGANESE(III) TETRAMESITYLPORPHYRIN AND THE OXIDATION-STATES OF MANGANESE TETRAMESITYLPORPHYRINS

The autoreduction reaction of the non-µ-oxo-dimer-forming chloromanganese(lll) tetramesitylporphyrin, (TMP)MnIII(Cl), with methanolic tetra-?-butylammonium hydroxide (YO-species = OH-or CH3O-) in acetonitrile and dimethyl sulfoxide under anaerobic conditions has been examined by UV/visible and2H NMR spectroscopies, where the spectral changes accompanying the reaction could be associated with changes in the oxidation and ligation states of the manganese porphyrin. Two intermediates, (TMP)MnIIand [(TMP)MnII(OY)]-, may be directly observed to form during the reaction by a mechanism thought to involve homolytic bond cleavage, which in a slower reaction convert to a product whose structure is suggested to be that of a [(TMP)-MnII(OY)2]-species. Exposure to air at any time during the reaction leads to the formation of the manganese(III) peroxo complex, [(TMP)MnIII(O2)]-The [(TMP)MnII(OY)]-species may be prepared independently from the reaction of (TMP)MnIIwith YO-, and2H NMR spectral studies on the titration of a toluene solution of (TMP-d8)MnIIwith YO-indicate only one YO-ligation. The pyrrole β-deuterium chemical shift for the [(TMP-d8)MnII(OY)]-complex in toluene at 25 °C is 37 ppm. The various oxidation states of the manganese tetramesitylporphyrins were examined in order to identify the intermediates and products of the reaction. Thin-layer spectroelectrochemical oxidation of the chloromanganese(III) tetramesitylporphyrin in methylene chloride shows the first I e oxidation to be porphyrin centered, providing the manganese(III) porphyrin T cation radical, ('+TMP)MnIII(Cl). Exchange of the chloro ligand for the hydroxy ligand shows that the first 1e oxidation of the hydroxymanganese(III) tetramesitylporphyrin at low temperature is metal centered, providing the (TMP)MnIV(O) species. Further le oxidation of the latter produces a species identified as the oxidized porphyrin radical cation, ('+TMP)MnIV(O). Spectroscopic data for the (TMP)-Mn,Iv(OY)2and [('+TMP)MnIII(Cl)](SbCl6-) species (UV/vis and2H NMR) and the ('-TMP)MnIIand (2-TMP)MnIIspecies (UV/vis) are reported. © 1990, American Chemical Society. All rights reserved.