Unusual Reactivity of a Thiazole-Based Mn Tricarbonyl Complex for CO2 Activation

Manganese tricarbonyl complexes have attracted considerable attention as competent electrocatalysts for CO2 reduction owing to their unique chemistry and the natural abundance of Mn. While the analogous Re complexes are well-known to activate CO2 under anhydrous conditions, most reported Mn tricarbonyl catalysts require exogenous protons. In an effort to understand the reason for the different CO2 reduction mechanisms, we investigate the reactivity of Mn(pbt)(CO)(3)Br, (1, where pbt = 2-(2-pyridyl)-benzothiazole) with CO2. Our combined electrochemical and spectroscopic data suggest that 1 can undergo a CO2 conversion to CO similar to Re complexes with and without the presence of a proton source but only at potentials significantly more negative than the second reduction. Furthermore, the one- and two-electron reduced species are chemically generated and characterized by NMR, UV-vis, and IR spectroscopy. By exploring sequential chemical reduction of 1, we uncover unusual reactivity of the reduced dimeric Mn-Mn species as well as the isolation of a species capable of C-H activation.