A Manganese(IV)-Hydroperoxo Intermediate Generated by Protonation of the Corresponding Manganese(III)-Superoxo Complex

Abstract

Earlier work revealed that metal-superoxo species primarily function as radicals and/or electrophiles. Herein, we present ambiphilicity of a MnIII-superoxo complex revealed by its proton- and metal-coupled electron-transfer processes. Specifically, a MnIV-hydroperoxo intermediate, [Mn­(BDPBrP)­(OOH)]+ (1, H2BDPBrP = 2,6-bis­((2-(S)-di­(4-bromo)­phenylhydroxylmethyl-1-pyrrolidinyl)­methyl)­pyridine) was generated by treatment of a MnIII-superoxo complex, Mn­(BDPBrP)­(O2 •) (2) with trifluoroacetic acid at −120 °C. Detailed insights into the electronic structure of 1 are obtained using resonance Raman and multi-frequency electron paramagnetic resonance spectroscopies coupled with density functional theory calculations. Similarly, the reaction of 2 with scandium­(III) triflate was shown to give a Mn­(IV)/Sc­(III) bridging peroxo species, [Mn­(BDPBrP)­(OO)­Sc­(OTf) n ](3‑n)+ (4). Furthermore, it is found that deprotonation of 1 quantitatively regenerates 2, and that one-electron oxidation of the corresponding MnIII-hydroperoxo species, Mn­(BDPBrP)­(OOH) (3), also yields 1.

Trapping an Elusive Fe(IV)-Superoxo Intermediate Inside a Self-Assembled Nanocage at Room Temperature

“…These features however mask the weak O-O stretch feature at 1086 cm -1 although the isotope sensitivity can be uncovered by subtracting the dominant cage peaks carefully (SI Figure S15). 17 We also see the side-on O-O stretch feature coupled to ligand vibrations at 697 cm -1 disappear with 18 Oisotope enrichment similar to that observed for Fe(III)-superoxo complex for TPP. 16c We see isotope shifts in all these features and other weaker signals between 600-900 cm -1 under the constraint of the signal to noise, clearly enunciating the presence of an Fe(IV)-superoxo species.…”

Structure and Reactivity of a High-Spin, Non-Heme Iron(III)-Superoxo Complex Supported by Phosphinimide Ligands

“…Finally, the [L Ad H]Fe complex was found to catalyze C-C and C-H bond cleavage processes. Inspired by previous reports of nucleophilic metal-dioxygen species that engage in aldehyde deformylation, 7,[40][41][42][43][44][45] we examined the reactivity of [L Ad H]Fe and 2-PPA in the presence of O2. Exposure of a 1:1 mixture of [L Ad H]Fe and 2-PPA to O2 resulted in the formation of acetophenone in >95% NMR yield.…”

Ambiphilicity of a mononuclear cobalt(iii) superoxo complex

“…In particular, the reaction of Mn III (BDP Br P)(O 2) (H 2 BDP Br P = 2,6-bis((2-(S)di(4-bromo)-phenylhydroxylmethyl-1-pyrrolidinyl)methyl)pyridine) with trifluoroacetic acid (TFA) and Sc(OTf) 3 yields rare examples of Mn IV -hydroperoxo complexes, Mn IV (BDP Br P)(OOH), and [Mn IV (m-OO) Sc(OTf) n ] (3Àn)+ as evidenced by the combined spectroscopic and computational studies (Scheme 1). 8 Obviously, these proton-and metal-coupled electron transfer processes provide the first experimental support for the proposed ambiphilicity of metal-superoxo species. In this regard, more examples are desired to fully understand how the ambiphilic property of metal-superoxo species affects their chemical reactivity.…”

“…On the other hand, they can initiate deformylation processes when treated with 2-phenylpropionaldehyde, thereby revealing their nucleophilic character. 7,8 Besides the aforementioned well know activities, in a given elementary transformation metal-superoxo intermediates may function not only as an electrophile but also as a nucleophile. In fact, ambiphilicity of metal-superoxo species has been postulated in a series of theoretical and experimentally investigations including O 2 activation catalyzed by a-ketoglutarate dependent dioxygenases, 9 and by Cu, Fe and Co model complexes.…”

“…10 Only recently has such ambiphilic property been experimentally confirmed. 8 In our continuing efforts devoted to investigating reactivity of metalsuperoxo intermediates, some of us succeeded in preparing a range of homologous Fe III -, Co III -and Mn III -superoxo species by reacting O 2 with the corresponding divalent precursors. 11 It has been shown that these trivalent metal-superoxo complexes can convert into the metal-hydroperoxo complexes via HAA.…”