Mimicking Class I b Mn 2 ‐Ribonucleotide Reductase: A Mn II 2 Complex and Its Reaction with Superoxide

A fascinating discovery in the chemistry of ribonucleotide reductases (RNRs) has been the identification of a dimanganese (Mn 2 ) active site in class I b RNRs that requires superoxide anion (O 2 .− ), rather than dioxygen (O 2 ), to access a high‐valent Mn 2 oxidant. Complex 1 ([Mn 2 (O 2 CCH 3 )(N‐Et‐HPTB)](ClO 4 ) 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 O 2 .− 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 II Mn III entity. Mn K‐edge X‐ray absorption near‐edge spectroscopy (XANES) suggested a formal oxidation state change of Mn II 2 in 1 to Mn II Mn III for 2 . Electrospray ionisation mass spectrometry (ESI‐MS) suggested 2 to be a Mn II Mn 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 O 2 .− activation at class I b Mn 2 RNRs.