Catalase and epoxidation activity of manganese salen complexes bearing two xanthene scaffolds

A series of manganese Hangman salen ligand platforms functionalized by tert-butyl groups in the 3 and 3' positions using the Suzuki cross-coupling methodology are presented. The Hangman platforms support multielectron chemistry mediated by proton-coupled electron transfer (PCET), as demonstrated by their ability to promote the catalytic disproportionation of hydrogen peroxide to oxygen and water via a high-valent metal oxo. The addition of the steric groups to the salen macrocycle leads to enhanced catalase activity by circumventing side reactions that sequester the catalyst off pathway. The stereochemistry imposed by the cyclohexanediamine backbone of the salen platform is revealed by the epoxidation of 1,2-dihydronapthalene by a variety of oxidants. Improved enantiomeric excess and catalase activity as compared to sterically unmodified counterparts establishes the efficacy of the tert-butyl groups in promoting PCET catalysis on the Hangman platform.