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

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 [MnII 2 (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)MnO2 Mn]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 MnIII MnIV 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.