Evidence of Sulfur Non‐Innocence in [Co<sup>II</sup>(dithiacyclam)]<sup>2+</sup>‐Mediated Catalytic Oxygen Reduction Reactions
Beatrice Battistella, Linda Iffland‐Mühlhaus, Maximillian Schütze, Beatrice Cula, Uwe Kuhlmann, Holger Dau, Peter Hildebrandt, Thomas Lohmiller, Stefan Mebs, Ulf‐Peter Apfel, Kallol Ray
Abstract
Abstract In many metalloenzymes, sulfur‐containing ligands participate in catalytic processes, mainly via the involvement in electron transfer reactions. In a biomimetic approach, we now demonstrate the implication of S‐ligation in cobalt mediated oxygen reduction reactions (ORR). A comparative study between the catalytic ORR capabilities of the four‐nitrogen bound [Co(cyclam)] 2+ ( 1 ; cyclam=1,5,8,11‐tetraaza‐cyclotetradecane) and the S‐containing analog [Co(S 2 N 2 ‐cyclam)] 2+ ( 2 ; S 2 N 2 ‐cyclam=1,8‐dithia‐5,11‐diaza‐cyclotetradecane) reveals improved catalytic performance once the chalcogen is introduced in the Co coordination sphere. Trapping and characterization of the intermediates formed upon dioxygen activation at the Co II centers in 1 and 2 point to the involvement of sulfur in the O 2 reduction process as the key for the improved catalytic ORR capabilities of 2 .