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

The structural and physicochemical properties of the manganese-corrolazine (Cz) complexes (TBP8Cz)MnV(identical)O (1) and (TBP8Cz)MnIII (2) (TBP = p-tertbutylphenyl) 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. Highfrequency 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 (angstrom), 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 (right arrow)MnIV process in 1 (near 0.0 V vs saturated calomel reference electrode). Chemical reduction of 1 results in the formation of a MnIIIMnIV((mu)-O) dimer as characterized by electron paramagnetic resonance spectroscopy.