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Understanding the Mechanism of H+-Induced Demetalation as a Design Strategy for Robust Iron(III) Peroxide-Activating Catalysts

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posted on 19.09.2003, 00:00 by Anindya Ghosh, Alexander D. Ryabov, Sherry M. Mayer, David C. Horner, Duane E. Prasuhn,, Sayam Sen Gupta, Leonard Vuocolo, Caleb Culver, Michael P. Hendrich, Cliffton E. F. Rickard, Richard E. Norman, Colin P. Horwitz, Terrence J. Collins
The FeIII-TAML (tetra-amido macrocyclic ligand) activators 1 (Y = Cl) and 2 (Y = H2O), a (R = Me, X = H), b (Me, Cl), c (Me, MeO), d (Et, Cl), e (F, H), f (F, Cl), are five-coordinated in the solid state (X-ray crystallography) but are six-coordinated species in water with two H2O axial ligands. The first pKa's of aqueous ligands are in the range of 9.5−10.5. The acid-induced demetalation of 2 follows the equation kobs = k1*[H+] + k3*[H+]3. The rate constants k1* and k3* vary by 5 and 11 orders of magnitude depending on the nature of substituents R. The highest stabilization against the demetalation is achieved for R = F.