Theoretical Study on the Structural-Function Relationship of Manganese(III)-Iodosylarene Adducts

Abstract

Metal-iodosylarene complexes have been recently viewed as a second oxidant alongside of the well-known high-valent metal-oxo species. Extensive efforts have been exerted to unveil the structure-function relationship of various metal-iodosylarene complexes. In the present manuscript, density functional theoretical calculations were employed to investigate such relationship of a specific manganese-iodosylbenzene complex [Mn III (TBDAP)(PhIO)(OH)] 2+ (1). Our results fit the experimental observations and revealed new mechanistic findings. 1 acts as a stepwise 1e+1e oxidant in sulfoxidation reactions. Surprisingly, C-H bond activation of 9,10-dihydroanthracene (DHA) by 1 proceeds via a novel ionic hydride transfer/proton transfer (HT/PT) mechanism. As a comparison to 1, the electrophilicity of an iodosylbenzene monomer PhIO was investigated. PhIO performs concerted 2e-oxidations both in sulfoxidation and C-H activation. Hydroxylation of DHA by PhIO was found to proceed via a novel ionic and concerted proton-transfer/hydroxylrebound mechanism involving 2e-oxidation to form a transient carbonium species.

Theoretical Study on the Aliphatic C─H Bond Activation by a Mononuclear Manganese(III) Iodosylbenzene Complex

“…As shown in Figure 1, pathway A via 5 TS1 is the most feasible route to the oxidation product in the reaction between CHD and 1 , which has an energy barrier of 20.7 kcal/mol. This barrier is 5.8 kcal/mol higher than that for DHA, which is consistent with the fact that CHD has a stronger C─H bond than DHA 7 …”

“…Further, Wang and co‐workers studied the mechanism of the C─H bond activation of dihydroanthracene (DHA) by 1 through density functional theory (DFT) calculations. Their DFT results suggested that there is a rate‐determining hydride transfer in the first step of the reaction 7 . However, there still remain uncertainties regarding the nature of the hydride transfer and other mechanistic possibilities.…”

“…This barrier is 5.8 kcal/mol higher than that for DHA, which is consistent with the fact that CHD has a stronger C H bond than DHA. 7 The transition states in pathways C and D (via 5 TS c and 5 TS d ) are less stable than 5 TS1 by 7.3 and 12.4 kcal/mol, respectively, highlighting the superiority of pathway A over pathways C and D as a reaction route. Furthermore, pathway B does not involve any stable transition state.…”

“…Their DFT results suggested that there is a rate-determining hydride transfer in the first step of the reaction. 7 However, there still remain uncertainties regarding the nature of the hydride transfer and other mechanistic possibilities. Herein, we report theoretical studies on the C H bond activation of 1,4-cyclohexadiene (CHD) by 1 with more specific analysis to give mechanistic insights for the aliphatic C H bond activation by 1.…”

“…This result is in contrast to the reaction of 1 with thioanisole, for which Wang and co-workers suggested that the halogen bond interaction between sulfur atom of thioanisole and iodine atom induces the O I bond cleavage leading to the formation of a high-valent manganese (V) oxo species. 7,8 Having identified pathway A as the operative one, we next investigated this particular pathway in further detail (Supporting Information Tables S1-S3 and Figure S1-S4). The relative energies of intermediates and transition states in different spin states for pathway A are depicted in Figure 2.…”