Remote amino acid recognition enables effective hydrogen peroxide activation at a manganese oxidation catalyst
Laia Vicens i Serra 1 , Giorgio Olivo 1,2 , Miquel Costas 1 1 Universitat de Girona, Spain, 2 Università "La Sapienza", Italy
Oxygenation of organic substrates by iron metalloenzymes occurs with high levels of selectivity, mainly because of the exquisite control of both the primary and the secondary sphere of the iron center [1]. Due to its efficiency, chemists have tried to mimic these systems with artificial catalysts, with a very defined first coordination sphere [2]. One of the most studied families are Fe and Mn complexes with tetradentate bis -amine -bis -pyridine ligands. These coordination compounds can efficiently activate the H 2 O 2 to form a high valent metal-oxo species able to oxidize a large range of substrates. However, a proton source is required for peroxide activation; and while a single acidic function is needed in enzymes, a high excess of carboxylic acid is required by artificial catalysts, especially with manganese complexes (up to 17500 equivalents with respect to the catalyst), resulting in a highly acidic solution and the production of high amounts of carboxylic acid waste [2]. Herein, we present an effective, enzyme-like hydrogen peroxide activation at a Mn catalyst with amounts of acid that are almost stoichiometric to the metal [3]. Our approach relies on supramolecular recognition of an a,w-amino acid to a crown ether receptor present in the ligand. Such interaction occurs in the second coordination sphere of the manganese, and locates the carboxylic acid in an optimal position to access the first coordination sphere and get involved in the catalytic cycle, enabling effective H 2 O 2 activation for asymmetric epoxidation reactions.
NMR analysis of the binding and catalytic oxidation experiments demonstrates that remote binding of the amino acid to the ligand is crucial for effective epoxidation. This work can serve as a proof-of-concept for the use of supramolecular chemistry to modify the second coordination sphere of bioinspired complexes and to design enzyme-like artificial catalysts. References 1. Costas, M.; Mhn, M.P.; Jensen, M.P.; Que, L., Chem. Rev., 2004, 104, 939-986. 2. Sun, W.; Sun, Q., Acc. Chem. Res., 2019, 52, 2370-2381. 3. Vicens, L.; Olivo, G.; Costas, M., Angew. Chem. Int. Ed., 2022, 61, e202114932.
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© The Author(s), 2022
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