Bromoacetic Acid-Promoted Nonheme Manganese-Catalyzed Alkane Hydroxylation Inspired by α-Ketoglutarate-Dependent Oxygenases

Abstract

Biomimetic iron and manganese complexes have emerged as important catalysts in chemo-, regio-, and stereoselective oxidation reactions. In this study, we describe a remote hydroxylation of undirected C(sp3)-H bonds utilizing a simple manganese complex as a catalyst and hydrogen peroxide (H2O2) as a terminal oxidant in the presence of bromoacetic acid (BrCH2CO2H) as an additive. Crucial features of this catalytic system are the excellent catalytic activity of an easily preparable manganese catalyst, [Mn(R,R-BPMCN)]2+ (1), a low catalyst loading, a short reaction time, a broad substrate scope, and an easy scale-up. Mechanistic studies were also performed to elucidate the role of BrCH2CO2H and the nature of the hydroxylating intermediate, revealing that the BrCH2CO2H additive facilitates the generation of a highly electrophilic Mn(V)-oxo bromoacetate intermediate as a responsible oxidant via a heterolytic O-O bond cleavage of a postulated Mn(III)-OOH precursor. One notable observation in the mechanistic studies was that a significant amount of 18O was incorporated from H218O into the alcohol product in these catalytic oxidation reactions. On the basis of the above experimental observations and from the support of density functional theory (DFT) calculations, we conclude that a highly electrophilic Mn(V)-oxo bromoacetate complex was generated as a responsible oxidant that effects the undirected C(sp3)-H hydroxylation via an oxygen-rebound mechanism, thus mimicking both the structure and the function of the active intermediate of iron(IV)-oxo succinate for α-ketoglutarate (αKG)-dependent nonheme iron oxygenases. © 2022 American Chemical Society.