Date of Award
Doctor of Philosophy
Lee K. Woo
Prior to this work, metalloporphyrin catalysts containing iron, ruthenium, osmium, cobalt, and rhodium were shown to be active for carbene transfer reactions. These metalloporphyrin catalysts were typically robust, highly reactive, and capable of inducing high selectivities. Furthermore, derivation at the porphyrin periphery by known routes allows for the development of a wide array of sophisticated chiral catalysts. Despite the promising results with other group 9 metal porphyrin complexes, carbene transfer catalysis with iridium porphyrin complexes had not been reported. The present work describes the development of iridium porphyrin-catalyzed cyclopropanation, C–H insertion, and N–H insertion reactions. These reactions were generally rapid and proceeded in moderate to high yields, at temperatures as low as -78 °C, and with turnover numbers on the order of 105. Extensive mechanistic studies revealed that the catalytic cycles proceed through metal-carbene intermediates for cyclopropanation and C–H insertion as well as metal-ylide intermediates to N–H insertion. Although structural studies on these reactive intermediates were not possible, the nature of iridium-carbene intermediates was explored indirectly using diaminocarbenes and N-heterocyclic carbenes (NHCs) as model ligands. Compared to rhodium, iridium seemed to form stronger bonds with these carbene ligands. This finding is consistent with a previously proposed transition state model and rationalizes the observed difference between rhodium and iridium porphyrin catalysts.
Bernie Joe Anding
Anding, Bernie Joe, "Iridium porphyrins: Catalysis, mechanism, and structural studies" (2013). Graduate Theses and Dissertations. 13314.