Hangman salophens.

We report here a modular approach for the construction of a new class of compounds, the Hangman salophens. In the Hangman motif, an acid-base functionality "hangs" over the face of a redox cofactor. In contrast to more synthetically intractable porphyrin-based Hangman systems, Hangman salophens permit the facile control of their proton and redox properties for the study of the proton-coupled electron transfer (PCET) activation of small molecules. By investigating the catalase-like disproportionation of H2O2, we show that the presence (1) of a strong proton-donating hanging group (i.e., carboxylic acid) and (2) of electron-donating groups on the redox-active salen imparts significant catalytic activity for the O-O bond activation of small molecule substrates. The contribution of the new ligand framework to furthering our understanding of how PCET can be implemented in the design of active/selective catalysts will be discussed.