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 (O 2 ⋅ - ) rather than dioxygen (O 2 ), to access a high valent Mn III -O 2 -Mn IV species, responsible for the oxidation of tyrosine to tyrosyl radical. In a biomimetic approach, we report the synthesis of a thiolate-bound dimanganese complex [Mn II 2 (BPMT)(OAc) 2 ](ClO) 4 (BPMT=(2,6-bis{[bis(2-pyridylmethyl)amino]methyl}-4-methylthiophenolate) (1) and its reaction with O 2 ⋅ - to form a [(BPMT)MnO 2 Mn] 2+ complex 2. Resonance Raman investigation revealed the presence of an O-O bond in 2, while EPR analysis displayed a 16-line S t =1/2 signal at g=2 typically associated with a Mn III Mn IV core, as detected in class Ib RNRs. Unlike all other previously reported Mn-O 2 -Mn complexes, generated by O 2 ⋅ - activation at Mn 2 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.