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