Aerobic Partial Oxidation of Alkanes Using Photodriven Iron Catalysis

Abstract

Photodriven oxidations of alkanes in trifluoroacetic acid using commercial and synthesized Fe­(III) sources as catalyst precursors and dioxygen (O2) as the terminal oxidant are reported. The reactions produce alkyl esters and occur at ambient temperature in the presence of air, and catalytic turnover is observed for the oxidation of methane in a pure O2 atmosphere. Under optimized conditions, approximately 17% conversion of methane to methyl trifluoroacetate at more than 50% selectivity is observed. It is demonstrated that methyl trifluoroacetate is stable under catalytic conditions, and thus overoxidized products are not formed through secondary oxidation of methyl trifluoroacetate.

Manganese Catalyzed Partial Oxidation of Light Alkanes

“…A pure sample of CF 3 H or mixtures of CF 3 H and methane and CO 2 injected into the TCD did not yield any signal for CF 3 H with our method. In previously published work, we found that the formation of CO 2 from solvent degradation led to the formation of CF 3 H through the decarboxylation of HTFA. However, in this current work, 1 H NMR analysis of pressurized J-Young tubes did not lead to the observation of CF 3 H. We note that the presence of paramagnetic Mn II species complicates the NMR analysis.…”

Partial Oxidation of Methane Enabled by Decatungstate Photocatalysis Coupled to Free Radical Chemistry

“…48 We also reported that Fe(TFA) 3 mediates photodriven hydrocarbon functionalization. 47 Similarly, FeCl 3 has been shown to functionalize methane and heavier alkanes to a variety of products. 49 The Schelter and Goldberg groups recently reported photodriven, aerobic alkane iodination in acetonitrile using catalytic [ n Bu 4 N]Cl.…”

“…Several examples of such reactions that are successful for unactivated hydrocarbons (e.g., cyclohexane) have been reported. − Using the strategy of generating chlorine from chloride, we recently pursued photodriven light alkane functionalization. , Higher yields were obtained for the chloride–iodate OxE process under photocatalytic conditions (∼50% yield was achieved for methane) compared to yields for the analogous thermally driven reaction . We also reported that Fe­(TFA) 3 mediates photodriven hydrocarbon functionalization . Similarly, FeCl 3 has been shown to functionalize methane and heavier alkanes to a variety of products .…”

“…Of particular interest was the possibility that photoexcited DT could also generate chlorine atoms, Cl•, under these reaction conditions due to the very high reduction potential of DT•• . There have been a number of recent advances in the photogeneration of Cl•, including photoreduction of metal chlorides ,,,,− and photoredox oxidation of chloride ion (Cl – ). ,− As noted above, the generation of chlorine has been used to functionalize unactivated hydrocarbons. − , DT is robust under acidic conditions and has a high quantum yield for photoexcitation, but it has not been employed for the generation of Cl• as a C–H activation mediator. Herein, we report experimentally and validate computationally the use of DT as a photocatalyst for methane partial oxidation in the presence of chloride and iodine to form methyl trifluoroacetate (MeTFA) and methyl chloride (MeCl or CH 3 Cl).…”

“…42−46 Using the strategy of generating chlorine from chloride, we recently pursued photodriven light alkane functionalization. 47,48 Higher yields were obtained for the chloride−iodate OxE process under photocatalytic conditions (∼50% yield was achieved for methane) compared to yields for the analogous thermally driven reaction. 48 We also reported that Fe(TFA) 3 mediates photodriven hydrocarbon functionalization.…”