摘要
Addition of anionic donors to the manganese(V)-oxo corrolazine complex Mn <sup>V</sup> (O)(TBP <sub>8</sub> Cz) has a dramatic influence on oxygen-atom transfer (OAT) reactivity with thioether substrates. The six-coordinate anionic [Mn <sup>V</sup> (O)(TBP <sub>8</sub> Cz)(X)] <sup>O</sup> complexes (X = F <sup>-</sup> , N <sub>3</sub> <sup>-</sup> , OCN <sup>-</sup> ) exhibit a 5 cm <sup>-1</sup> downshift of the Mn-O vibrational mode relative to the parent Mn <sup>V</sup> (O)(TBP <sub>8</sub> Cz) complex as seen by resonance Raman spectroscopy. Product analysis shows that the oxidation of thioether substrates gives sulfoxide product, consistent with single OAT. A wide range of OAT reactivity is seen for the different axial ligands, with the following trend determined from a comparison of their second-order rate constants for sulfoxidation: five-coordinate thiocyanate nitrate < cyanate < azide < fluoride cyanide. This trend correlates with DFT calculations on the binding of the axial donors to the parent Mn <sup>V</sup> (O)(TBP <sub>8</sub> Cz) complex. A Hammett study was performed with p-X-C <sub>6</sub> H <sub>4</sub> SCH <sub>3</sub> derivatives and [Mn <sup>V</sup> (O)(TBP <sub>8</sub> Cz)(X)] <sup>O</sup> (X = CN <sup>-</sup> or F <sup>-</sup> ) as the oxidant, and unusual V-shaped Hammett plots were obtained. These results are rationalized based upon a change in mechanism that hinges on the ability of the [Mn <sup>V</sup> (O)(TBP <sub>8</sub> Cz)(X)] <sup>O</sup> complexes to function as either an electrophilic or weak nucleophilic oxidant depending upon the nature of the para-X substituents. For comparison, the one-electron-oxidized cationic Mn <sup>V</sup> (O)(TBP <sub>8</sub> Cz <sup>+</sup> ) complex yielded a linear Hammett relationship for all substrates (= 1.40), consistent with a straightforward electrophilic mechanism. This study provides new, fundamental insights regarding the influence of axial donors on high-valent Mn <sup>V</sup> (O) porphyrinoid complexes.