Alkane Oxidation Catalyzed by Manganese-tmtacn Complexes with H2O2

Abstract

The C-H bond activation of alkanes for selective hydroxylation by metal complexes has been the subject of intense research for application in synthetic chemistry and industrial processes. As metal-containing enzymes functionalize the energetically difficult C-H bonds of alkanes, biomimetic alkane hydroxylations using the model complexes of the enzymes have received much attention in the communities of bioinorganic and oxidation chemistry. Among the reported model complexes, manganese complexes using N, N’,N”-trimethyl-1,4,7-triazacyclononane (tmtacn) are known to catalyze various oxidation reactions, such as epoxidation of olefins, hydroxylation of saturated and aromatic hydrocarbons, and oxidation of alcohols, by peroxides. In the oxidation reactions of alkane and alkene, the nature of carboxylate buffers was reported to have a significant effect on the activities of the Mn-tmtacn catalysts. The differences in the activity observed in different carboxylate buffers were suggested perhaps to arise from differences in the structures of the active Mn species involved in the oxidation reactions. As an attempt to get an additional insight into the reactivity and selectivity features of the catalytic alkane oxidation process based on our experience with porphyrin catalysts, we have studied the alkane oxidation using the Mn-tmtacn catalyst and H2O2 in the presence of an oxalate buffer under mild conditions. We now report that this Mn catalyst is able to oxidize alkanes with moderate yields at 0 C and perform a stereospecific hydroxylation via a mechanism involving metal-based oxidants.