A Mn^IIMn^III‐Peroxide Complex Capable of Aldehyde Deformylation

Abstract

Ribonucleotide reductases (RNRs) are essential enzymes required for DNA synthesis. In class Ib Mn2 RNRs superoxide (O2.−) was postulated to react with the MnII2 core to yield a MnIIMnIII‐peroxide moiety. The reactivity of complex 1 ([MnII2(O2CCH3)2(BPMP)](ClO4), where HBPMP=2,6‐bis{[(bis(2‐pyridylmethyl)amino]methyl}‐4‐methylphenol) towards O2.− was investigated at −90 °C, generating a metastable species, 2. The electronic absorption spectrum of 2 displayed features (λmax=440, 590 nm) characteristic of a MnIIMnIII‐peroxide species, representing just the second example of such. Electron paramagnetic resonance and X‐ray absorption spectroscopies, and mass spectrometry supported the formulation of 2 as a MnIIMnIII‐peroxide complex. Unlike all other previously reported Mn2‐peroxides, which were unreactive, 2 proved to be a capable oxidant in aldehyde deformylation. Our studies provide insight into the mechanism of O2‐activation in Class Ib Mn2 RNRs, and the highly reactive intermediates in their catalytic cycle.

Stoichiometric Aldehyde Deformylation Mediated by Nucleophilic Peroxo‐diiron(III) Complex as a Functional Model of Aldehyde Deformylating Oxygenase

“…In the present study, we tested the nucleophilic reactivity of the well‐defined peroxo‐diiron(III) species, 1 , with various electrophilic substrates. To probe the nucleophilic reactivity of mono and dinuclear metal‐peroxides, p ‐X‐PhC(O)Cl and p ‐X‐PhC(O)H can be used as model substrates . Non‐heme dinuclear peroxo‐diiron(III) intermediate, [Fe III 2 (μ‐O 2 )(MeBzim‐Py) 4 (CH 3 CN) 2 ] 4+ ( 1 ), decays over the course of 80 min at 15 °C with k decay =1.066×10 −4 s −1 .…”

“…To probe the nucleophilic reactivity of mono and dinuclear metal-peroxides, p-X-PhC(O)Cla nd p-X-PhC(O)H can be used as model substrates. [14] Non-hemed inuclear peroxo-diiron(III) intermediate, [Fe III 2 (m-O 2 )(MeBzim-Py) 4 (CH 3 CN) 2 ] 4 + (1), decays over the course of 80 min at 15 8C with k decay = 1.066 10 À4 s À1 .T he decay process of 1 can be acceleratedb yt he addition of 50 equiv of PhC(O)H or PhC(O)Cl resultingi nt he formation of benzoic acid in both cases based on GC-MSa nalysis (yields % 80-90 %b ased on 1,F igure S1 in the Supporting Information). The reactivity of 1 was monitored by UV/Vis spectroscopy and the rate of its rapid decomposition was measureda t7 10 nm ( Figure 1A).…”

“…This value is almost identical with the data reported for the previously published [Mn II Mn III (O 2 )(BPMP)] 2 + /p-X-PhC(O)H system (1 =+0.64;H BPMP = 2,6-bis[(bis(2-pyridylmethyl)amino)methyl]-4-methylphenol),s uggesting as imilar mechanism including an ucleophilic attack of the peroxide on the aldehyde C-atom in the rate-determinings tep (Scheme 2). [14] It is worth noting that much higher 1 values (1.7-2.5) were obtainedf or mononuclear peroxo complexes. [15] In contrast, the Hammett plot for the para-substituted benzoyl chlorided erivatives gave a 1-value of zero, suggesting ad ifferent reactionm echanism, where the nucleophilic attack of the peroxo-diiron(III) as rate-determining step can be excluded (Figure 2).…”

Eccentricities in Spectroscopy and Reactivity of Non‐Heme Metal Intermediates Contained in Bispidine Scaffolds

“…react with aldehydes by a direct nucleophilic attack at the carbonyl centre. [83][84][85][86][87][92][93][94] Such nucleophilic deformylation reactions have been reported for several metal complexes. However, recently, a novel mechanistic pathway was discovered for aldehyde deformylation reaction.…”

“…Several metal-peroxo complexes have been observed to exhibit deformylation abilities with model aldehyde substrates like 2-phenylpropionaldehyde (2-PPA) or cyclohexanecaboxaldehye (CCA). [80][81][82][83][84][85][86][87][88][89][90][91] It was a common notion that the metal-dioxygen adducts like metal-peroxo, or metal-hydroperoxo, etc. react with aldehydes by a direct nucleophilic attack at the carbonyl centre.…”