Singly Unified Driving Force Dependence of Outer-Sphere Electron-Transfer Pathways of Nonheme Manganese(IV)−Oxo Complexes in the Absence and Presence of Lewis Acids

Abstract

Epoxidation of styrene derivatives, sulfoxidation of thioanisole derivatives, and hydroxylation of toluene derivatives by a nonheme manganese(IV)-oxo complex binding triflic acid, [(N4Py)Mn^IV(O)]²⁺-(HOTf)₂ [<b>1</b>-(H⁺)₂], and scandium triflate, [(N4Py)Mn^IV(O)]²⁺-(Sc(OTf)₃)₂ [<b>1</b>-(Sc³⁺)₂], occur via outer-sphere electron-transfer (OSET) pathways, exhibiting singly unified driving force dependence, enabling one to predict absolute values of the second-order rate constants of these three types of substrate oxidations by the manganese(IV)-oxo complex, using the Marcus theory of electron transfer. When [(N4Py)Mn^IV(O)]²⁺ (<b>1</b>) was replaced by [(N4Py)Fe^IV(O)]²⁺ (<b>2</b>), OSET pathways were changed to inner-sphere electron-transfer (ISET) pathways. The difference in the OSET versus ISET pathways is clarified based on the difference in the Lewis basicity of the oxo moieties in <b>1</b> and <b>2</b>.