Selective CH Functionalization of Methane, Ethane, and Propane by a Perfluoroarene Iodine(III) Complex

Abstract

Direct partial oxidation of methane, ethane, and propane to their respective trifluoroacetate esters is achieved by a homogeneous hypervalent iodine(III) complex in non-superacidic (trifluoroacetic acid) solvent. The reaction is highly selective for ester formation (>99%). In the case of ethane, greater than 0.5 M EtTFA can be achieved. Preliminary kinetic analysis and density functional calculations support a nonradical electrophilic CH activation and iodine alkyl functionalization mechanism.

Selective C−H Functionalization of Methane and Ethane by a Molecular SbV Complex

“…The lowest-energy functionalization route identified involves TFA anion dissociation followed by barrierless substitution leading to EtTFAa nd Sb III (TFA) 3 .F or an accurate estimate of TFA dissociation, we used am icrosolvation model:( TFA) 4 Sb V -(Et) + (TFAH) 5 ! [(TFA) 3 (TFAH)Sb V (Et)] + + [(TFAH) 4 -(TFA)] À ,w hich requires 18 kcal mol À1 .T his relatively lowenergy pathway for Sb V -C functionalization, compared to the reverse barrier for ethyl group protonation (reverse of C À H activation) is consistent with the fact that no H/D exchange of ethane was observed for reactions in TFAD.This substitution pathway that gives EtTFAissignificantly lower in energy than the transition state for deprotonation/elimination to give ethylene ( Figure 4B), which we estimated to be at 40 kcal mol À1 above the ground state,a nd would lead to EG(TFA) 2 . This high-energy pathway is consistent with EG(TFA) 2 being formed sequentially after EtTFA.…”

“…[1] An associated challenge is that following functionalization, the remaining CÀHbonds can be more reactive than the starting alkane.B ecause of these challenges,t here are al imited number of molecular catalysts that can effect the selective oxy-functionalization of methane and ethane C À Hb onds, with most utilizing transition metals. [2] However,d ue to the large mass and toxicity of these metals, we began asearch for lower mass and less toxic period 5maingroup-metal complexes ( Figure 1B)w ith similar reactivity towards alkanes.W ew ere attracted to Sb because of its historical use in the chemical industry,a nd the possibility of accessing compounds with ah igh oxidation state (Sb V ,d 10 s 0 electronic occupation). [2] However,d ue to the large mass and toxicity of these metals, we began asearch for lower mass and less toxic period 5maingroup-metal complexes ( Figure 1B)w ith similar reactivity towards alkanes.W ew ere attracted to Sb because of its historical use in the chemical industry,a nd the possibility of accessing compounds with ah igh oxidation state (Sb V ,d 10 s 0 electronic occupation).…”

“…[1b] In adeparture from using transition-metal-based catalysts, we previously demonstrated that Tl III and Pb IV trifluoroacetate main-group compounds promote efficient functionalization of light alkanes in trifluoroacetic acid (TFAH) solvent. [2] However,d ue to the large mass and toxicity of these metals, we began asearch for lower mass and less toxic period 5maingroup-metal complexes ( Figure 1B)w ith similar reactivity towards alkanes.W ew ere attracted to Sb because of its historical use in the chemical industry,a nd the possibility of accessing compounds with ah igh oxidation state (Sb V ,d 10 s 0 electronic occupation). [3] We were also highly encouraged by our preliminary computational prediction of methane C À H activation and metal-methyl functionalization reactions, which indicated that Sb V (TFA) 5 has an accessible activation barrier (see the Supporting Information).…”

Contrasting electronic requirements for CH binding and CH activation in d6 half‐sandwich complexes of rhenium and tungsten

“…Activation of CH bonds and selective functionalization of an alkane are eagerly sought after goals . Hopes that these could indeed be realized by studying organometallic complexes increased when Perutz and coworkers characterized metal‐alkane complexes by carrying out UV photolysis of M(CO) 6 (M = Cr, Mo, and W) in low temperature methane matrices .…”

Preface for Small-Molecule Activation: Carbon-Containing Fuels

“…These have been proposed to operate via a mechanism that is, interestingly, related to the CMD pathway proposed for palladium complexes. 7 The Forum Article by Que affords an overview of alkane C− H bond cleavage by oxoiron(IV) complexes, both heme-and nonheme-coordinated. Such species operate via hydrogen-atom transfer to the oxo group.…”