Electrochemical activation of O2 catalyzed by bioinspired Mn(III)-Schiff base complexes

FERREYRA, JOAQUÍN; HUREAU, CHRISTELLE; PALOPOLI, CLAUDIA; SIGNORELLA, SANDRA; RICHEZZI, MICAELA; ANXOLABÉHÈRE-MALLART, ELODIE

Simposio; American Symposium on Coordination and Organometallic Chemistry; 2022

Molecular oxygen (O2) is considered an excellent oxidant due to its abundant, inexpensive and environmentally benign characteristics, yet reductive activation is necessary for it to be able to react with diamagnetic species. Nature can overcome this spin state barrier by employing diverse transition metal ions (e.g. Mn, Cu and Fe) that also exist in open-shell spin ground states and can react directly with triplet O2 [1]. For this reason, development of biomimetic transition-metal-containing catalysts is a promising approach to the use of this oxidant in moderate conditions. In this work, three Mn(III)-Schiff base complexes ([MnIII(X-salpn)]+, salpn = 1,3-bis(salicylidenamino)propane, X = H, 5-Cl and 3,5-Cl2) and their bisoxo-bridged diMn(IV) dimers were obtained and fully characterized, and the ability of the monomers to catalyze the electrochemical activation of O2 was examined. As it raises Mn(III)/Mn(II) couple redox potential, the introduction of electron-withdrawing ?Cl substituents lowers the ability of the catalyst to interact with O2, with Mn(3,5-Cl2salpn)]+ complex being utterly unreactive. In addition, experimental data from electrochemical and spectroelectrochemical studies of [Mn(salpn)]+ and [Mn(5-Clsalpn)]+ complexes under aerobic conditions suggest that, after the electrochemical reduction of the metallic center, the reaction takes place by a mechanism which involves the formation of bisoxo-bridged diMn(IV) intermediates.