Corrolazines: New frontiers in high-valent metalloporphyrinoid stability and reactivity

The activation of dioxygen and its analogues, such as hydrogen peroxide, by metalloporphyrins leads to the generation of high-valent metaloxo species. This process is critically important to heme-catalyzed reactions, such as for cytochrome P450, and synthetic porphyrin-catalyzed oxidations. We have synthesized a new ring-contracted porphyrinoid system called a corrolazine that is designed to stabilize high oxidation states, including high-valent metaloxo species. The corrolazine ligand stabilizes manganese(V) terminal oxo and terminal imido complexes for isolation, both of which are only transiently observed with normal porphyrin macrocycles. Examination of both oxygen atom transfer and hydrogen atom abstraction reactions for the Mn(V)oxo complex has led to a number of mechanistic insights regarding these transformations. The activation of H2O2 to give the Mn(V)oxo complex exhibits some dramatic and unexpected axial ligand effects that call into question the normal role of axial ligands in OO bond cleavage pathways.