Oxygen-Atom Transfer Reactivity of Axially Ligated Mn(V)鈥揙xo Complexes: Evidence for Enhanced Electrophilic and Nucleophilic Pathways

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• 作者：Heather M. Neu ; Tzuhsiung Yang ; Regina A. Baglia ; Timothy H. Yosca ; Michael T. Green ; Matthew G. Quesne ; Sam P. de Visser ; David P. Goldberg
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：October 1, 2014
• 年：2014
• 卷：136
• 期：39
• 页码：13845-13852
• 全文大小：552K
• ISSN：1520-5126

文摘

Addition of anionic donors to the manganese(V)鈥搊xo corrolazine complex Mn^V(O)(TBP₈Cz) has a dramatic influence on oxygen-atom transfer (OAT) reactivity with thioether substrates. The six-coordinate anionic [Mn^V(O)(TBP₈Cz)(X)]^{鈭?/sup> complexes (X = F鈥?/sup>, N₃鈥?/sup>, OCN鈥?/sup>) exhibit a 鈭? cm鈥? downshift of the Mn鈥揙 vibrational mode relative to the parent MnV(O)(TBP₈Cz) 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 鈮?thiocyanate 鈮?nitrate < cyanate < azide < fluoride 鈮?cyanide. This trend correlates with DFT calculations on the binding of the axial donors to the parent MnV(O)(TBP₈Cz) complex. A Hammett study was performed with p-X-C₆H₄SCH₃ derivatives and [MnV(O)(TBP₈Cz)(X)]鈭?/sup> (X = CN鈥?/sup> or F鈥?/sup>) as the oxidant, and unusual 鈥淰-shaped鈥?Hammett plots were obtained. These results are rationalized based upon a change in mechanism that hinges on the ability of the [MnV(O)(TBP₈Cz)(X)]鈭?/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 MnV(O)(TBP₈Cz鈥?) complex yielded a linear Hammett relationship for all substrates (蟻 = 鈭?.40), consistent with a straightforward electrophilic mechanism. This study provides new, fundamental insights regarding the influence of axial donors on high-valent MnV(O) porphyrinoid complexes.}