Mimicking Class I b Mn₂‐Ribonucleotide Reductase: A Mn^II₂ Complex and Its Reaction with Superoxide

E-ISSN： 1521-3773|57|4|918-922

ISSN： 1433-7851

Source： ANGEWANDTE CHEMIE INTERNATIONAL EDITION, Vol.57, Iss.4, 2018-01, pp. : 918-922

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Abstract

AbstractA 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 (λ_max=460, 610 nm) typical of a Mn‐peroxide species and a 29‐line EPR signal typical of a Mn^IIMn^III entity. Mn K‐edge X‐ray absorption near‐edge spectroscopy (XANES) suggested a formal oxidation state change of Mn^II₂ in 1 to Mn^IIMn^III for 2. Electrospray ionisation mass spectrometry (ESI‐MS) suggested 2 to be a Mn^IIMn^III‐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.