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)MnIV(O)]2+-(HOTf)2 [1-(H+)2], and scandium triflate, [(N4Py)MnIV(O)]2+-(Sc(OTf)3)2 [1-(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)MnIV(O)]2+ (1) was replaced by [(N4Py)FeIV(O)]2+ (2), 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 1 and 2.