Structures and Reactivity of Group 9 Metalloporphyrin Complexes

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 Rh^III(TTP) and Ir^III(TTP) carbene complexes provides insights for understanding reactivity differences for the two metals complexes.⁶

References

1.  Anding, B. J.; Woo, L. K. In Handbook of Porphyrin Science; Kadish, K. M., Guilard, R., Smith, K., Eds.; World Scientific Publishing Company: Hackensack, NJ, 2012; Vol. 21, p 145.

2.  Mirafzal, G. A.; Cheng, G.; Woo, L. K. J. Am. Chem. Soc. 2002, 124, 176-177.

3.  Dairo, T. O.; Ellern, A.; Angelici, R. J.; Woo, L. K. Organometllics, 2014, 33, 2266-2276.

4.  Anding, B. J.; Ellern, A.; Woo, L. K. Organometallics 2012, 31, 3628-3635.

5.  Anding, B. J.; Woo, L. K. Organometallics, 2013, 32, 2599-2607.

6.  Anding, B. J.; Ellern, A.; Woo, L. K. Organometallics, 2014, 33, 2219-2229.