Corrolazines: New Frontiers in High-Valent Metalloporphyrinoid Stability and Reactivity

David P. Goldberg received his B.A. degree in chemistry from Williams College in 1989 and his Ph.D. in chemistry from the Massachusetts Institute of Technology in 1995. He continued his studies as a NIH Postdoctoral Fellow at Northwestern University before beginning his independent career at Johns Hopkins University in 1998, where he is currently an Associate Professor in the Chemistry Department. His research interests in bioinorganic chemistry include porphyrinoid synthesis and reactivity and the construction of synthetic analogues of metalloenzymes.

The activation of dioxygen and its analogues, such as hydrogen peroxide, by metalloporphyrins leads to the generation of high-valent metal–oxo 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 metal–oxo 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 O–O bond cleavage pathways.