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Synthesis, Characterization, and Physicochemical Properties of Manganese(III) and Manganese(V)−Oxo Corrolazines

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posted on 2005-06-27, 00:00 authored by David E. Lansky, Beaven Mandimutsira, Bobby Ramdhanie, Maria Clausén, James Penner-Hahn, S. A. Zvyagin, Joshua Telser, J. Krzystek, Riqiang Zhan, Zhongping Ou, Karl M. Kadish, Lev Zakharov, Arnold L. Rheingold, David P. Goldberg
The structural and physicochemical properties of the manganese−corrolazine (Cz) complexes (TBP8Cz)MnV⋮O (1) and (TBP8Cz)MnIII (2) (TBP = p-tert-butylphenyl) have been determined. Recrystallization of 2 from toluene/MeOH resulted in the crystal structure of (TBP8Cz)MnIII(CH3OH) (2·MeOH). The packing diagram of 2·MeOH reveals hydrogen bonds between MeOH axial ligands and meso N atoms of adjacent molecules. Solution binding studies of 2 with different axial ligands (Cl-, Et3PO, and Ph3PO) reveal strong binding, corroborating the preference of the MnIII ion for a five-coordinate environment. High-frequency and field electron paramagnetic resonance (HFEPR) spectroscopy of solid 2·MeOH shows that 2·MeOH is best described as a high-spin (S = 2) MnIII complex with zero-field splitting parameters typical of corroles. Structural information on 1 was obtained through an X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure (EXAFS) study and compared to XANES/EXAFS data for 2·MeOH. The XANES data for 1 shows an intense pre-edge transition characteristic of a high-valent metal−oxo species, and a best fit of the EXAFS data gives a short Mn−O bond distance of 1.56 Å, confirming the structure of the metal−oxo unit in 1. Detailed spectroelectrochemical studies of 1 and 2 were performed revealing multiple reversible redox processes for both complexes, including a relatively low potential for the MnV → MnIV process in 1 (near 0.0 V vs saturated calomel reference electrode). Chemical reduction of 1 results in the formation of a MnIIIMnIV(μ-O) dimer as characterized by electron paramagnetic resonance spectroscopy.