A New Thiolate-Bound Dimanganese Cluster as a Structural and Functional Model for Class Ib Ribonucleotide Reductases

Abstract

In class Ib ribonucleotide reductases (RNRs) a dimanganese(II) cluster activates superoxide (O2⋅−) rather than dioxygen (O2), to access a high valent MnIII−O2−MnIV species, responsible for the oxidation of tyrosine to tyrosyl radical. In a biomimetic approach, we report the synthesis of a thiolate-bound dimanganese complex [MnII2(BPMT)(OAc)2](ClO)4 (BPMT=(2,6-bis{[bis(2-pyridylmethyl)amino]methyl}-4-methylthiophenolate) (1) and its reaction with O2⋅− to form a [(BPMT)MnO2Mn]2+ complex 2. Resonance Raman investigation revealed the presence of an O−O bond in 2, while EPR analysis displayed a 16-line St=1/2 signal at g=2 typically associated with a MnIIIMnIV core, as detected in class Ib RNRs. Unlike all other previously reported Mn−O2−Mn complexes, generated by O2⋅− activation at Mn2 centers, 2 proved to be a capable electrophilic oxidant in aldehyde deformylation and phenol oxidation reactions, rendering it one of the best structural and functional models for class Ib RNRs.