Structures and Reactivity of Group 9 Metalloporphyrin Complexes

Abstract

The importance of metalloporphyrins is highlighted by their wide occurrence and use in nature. Essential biological roles of metalloporphyrins include electron-, energy-, and oxygen-transfer, oxygen activation, and diverse functions in enzyme active sites. Due to a broad range of physical and chemical properties, metalloporphyrins have been modified for a variety of applications such as novel components in advanced materials, sensors, medical research, and synthetic chemistry. Metalloporphyrins are also of great utility for non-biological chemical catalysis, spanning reactions such as aziridination,1 C-H activation,1 and olefination.2 Moreover, metalloporphyrins are useful, atom-efficient catalysts for the generation of new carbon-carbon and heteroatom bonds using diazo carbonyl compounds.1 Thus, understanding the structures and reactivities of metalloporphyins is vital for developing and optimizing new uses. Our current work focuses on group 9 (Rh, Ir) metalloporphyrins. This includes probing the reactivity of coordination complexes and determining the structures of the subsequent products.3 Recently, tetratolylporphyrinato (TTP) methyliridium, Ir(TTP)CH3, was shown to be an active and robust catalyst for the cyclopropanation of olefins using diazo reagents as carbene sources.4 Ir(TTP)CH3 also catalyzes N–H insertion reactions between ethyl diazoacetate (EDA) or methyl phenyldiazoacetate (MPDA) and a variety of aryl, aliphatic, primary, and secondary amines.5 Reactions with aryl amines produce the highest yields with up to 105 catalyst turnovers and without the need for slow addition of the diazo reagent. Mechanistic aspects of diazo insertion reactions are examined. In addition, a comparison of the molecular structures of RhIII(TTP) and IrIII(TTP) carbene complexes provides insights for understanding reactivity differences for the two metals complexes.6