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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. [ABSTRACT FROM AUTHOR]

Abstract: A fascinating discovery in the chemistry of ribonucleotide reductases (RNRs) has been the identification of a dimanganese (Mn2) active site in class I b RNRs that requires superoxide anion (O2.−), rather than dioxygen (O2), to access a high‐valent Mn2 oxidant. Complex 1 ([Mn2(O2CCH3)(N‐Et‐HPTB)](ClO4)2, N‐Et‐HPTB=N,N,N′,N′‐tetrakis(2‐(1‐ethylbenzimidazolyl))‐2‐hydroxy‐1,3‐diaminopropane) was synthesised in high yield (90 %). 1 was reacted with O2.− at −40 °C resulting in the formation of a metastable species (2). 2 displayed electronic absorption features (λmax=460, 610 nm) typical of a Mn‐peroxide species and a 29‐line EPR signal typical of a MnIIMnIII entity. Mn K‐edge X‐ray absorption near‐edge spectroscopy (XANES) suggested a formal oxidation state change of MnII2 in 1 to MnIIMnIII for 2. Electrospray ionisation mass spectrometry (ESI‐MS) suggested 2 to be a MnIIMnIII‐peroxide complex. 2 was capable of oxidizing ferrocene and weak O−H bonds upon activation with proton donors. Our findings provide support for the postulated mechanism of O2.− activation at class I b Mn2 RNRs. [ABSTRACT FROM AUTHOR]