A MnII MnIII -Peroxide Complex Capable of Aldehyde Deformylation.

Ribonucleotide reductases (RNRs) are essential enzymes required for DNA synthesis. In class Ib Mn2 RNRs superoxide (O2 .- ) was postulated to react with the MnII 2 core to yield a MnII MnIII -peroxide moiety. The reactivity of complex 1 ([MnII 2 (O2 CCH3 )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 MnII MnIII -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 MnII MnIII -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.