A Mn II Mn III ‐Peroxide Complex Capable of Aldehyde Deformylation

Ribonucleotide reductases (RNRs) are essential enzymes required for DNA synthesis. In class Ib Mn 2 RNRs superoxide (O 2 .− ) was postulated to react with the Mn II 2 core to yield a Mn II Mn III ‐peroxide moiety. The reactivity of complex 1 ([Mn II 2 (O 2 CCH 3 ) 2 (BPMP)](ClO 4 ), where HBPMP=2,6‐bis{[(bis(2‐pyridylmethyl)amino]methyl}‐4‐methylphenol) towards O 2 .− was investigated at −90 °C, generating a metastable species, 2 . The electronic absorption spectrum of 2 displayed features ( λ max =440, 590 nm) characteristic of a Mn II Mn III ‐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 Mn II Mn III ‐peroxide complex. Unlike all other previously reported Mn 2 ‐peroxides, which were unreactive, 2 proved to be a capable oxidant in aldehyde deformylation. Our studies provide insight into the mechanism of O 2 ‐activation in Class Ib Mn 2 RNRs, and the highly reactive intermediates in their catalytic cycle.