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)Mn^V⋮O (1) and (TBP₈Cz)Mn^III (2) (TBP = p-tert-butylphenyl) have been determined. Recrystallization of 2 from toluene/MeOH resulted in the crystal structure of (TBP₈Cz)Mn^III(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 Mn^III 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) Mn^III 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 Mn^V → Mn^IV process in 1 (near 0.0 V vs saturated calomel reference electrode). Chemical reduction of 1 results in the formation of a Mn^IIIMn^IV(μ-O) dimer as characterized by electron paramagnetic resonance spectroscopy.