Formation of a Reactive [Mn(III)-O-Ce(IV)] Species and its Facile Equilibrium with Related Mn(IV)(OX) (X = Sc or H) Complexes

Lewis acid-bound high valent Mn-oxo species are of great importance due to their relevance to photosystem II. Here, we report the synthesis of a unique [(BnTPEN)Mn(III)-O-Ce(IV)(NO3)4]+ adduct (2) by the reaction of (BnTPEN)Mn(II) (1) with 4 eq. ceric ammonium nitrate. 2 has been characterized using UV/Vis, NMR, resonance Raman spectroscopy, as well as by mass spectrometry. Treatment of 2 with Sc(III)(OTf)3 results in the formation of (BnTPEN)Mn(IV)-O-Sc(III) (3), while HClO4 addition to 2 forms (BnTPEN)Mn(IV)-OH (4), reverting to 2 upon Ce(III)(NO3)3 addition. 2 can also be prepared by the oxidation of 1 eq. Ce(III)(NO3)3 with [(BnTPEN)Mn(IV)=O]2+ (5). In addition, the EPR spectroscopy revealed the elegant temperature-dependent equilibria between 2 and Mn(IV) species. The binding of redox-active Ce(IV) boosts electron transfer efficiency of 2 towards ferrocenes. Remarkably, the newly characterized Mn(III)-O-Ce(IV) species can carry out O-atom and H-atom transfer reactions. Lewis-acid-bound high-valent manganese-oxo species are important in understanding the role of Ca(II) ion in photosystem II. We present the synthesis and spectroscopic assessment of a novel Mn(III)-O-Ce(IV) species. This species opens up a new pathway for the synthesis of Mn(IV)-O-Sc(III) and Mn(IV)-OH, which are relevant to photosystem II.image

Automated summary

Lewis acid-bound high valent Mn-oxo species, relevant to photosystem II, were synthesized and characterized. The unique [(BnTPEN)Mn(III)-O-Ce(IV)(NO3)4]+ adduct was obtained and analyzed using various spectroscopic techniques. The Mn(III)-O-Ce(IV) species exhibited O-atom and H-atom transfer reactions, as well as enhanced electron transfer efficiency towards ferrocenes.