Document Type
Article
Publication Date
1-9-2017
Abstract
© 2016 American Chemical Society. We previously reported a dimeric IrIV-oxo species as the active water oxidation catalyst formed from a Cp∗Ir(pyalc)Cl {pyalc = 2-(2′-pyridyl)-2-propanoate} precursor, where the Cp∗ is lost to oxidative degradation during catalyst activation; this system can also oxidize unactivated CH bonds. We now show that the same Cp∗Ir(pyalc)Cl precursor leads to two distinct active catalysts for CH oxidation. In the presence of external CH substrate, the Cp∗ remains ligated to the Ir center during catalysis; the active species-likely a highvalent Cp∗Ir(pyalc) species-will oxidize the substrate instead of its own Cp∗. If there is no external CH substrate in the reaction mixture, the Cp∗ will be oxidized and lost, and the active species is then an iridium-μ-oxo dimer. Additionally, the recently reported Ir(CO)2(pyalc) water oxidation precatalyst is now found to be an efficient, stereoretentive CH oxidation precursor. We compare the reactivity of Ir(CO)2(pyalc) and Cp∗Ir(pyalc)Cl precursors and show that both can lose their placeholder ligands, CO or Cp∗, to form substantially similar dimeric IrIV-oxo catalyst resting states. The more efficient activation of the bis-carbonyl precursor makes it less inhibited by obligatory byproducts formed from Cp∗ degradation, and therefore the dicarbonyl is our preferred precatalyst for oxidation catalysis.
Publication Source (Journal or Book title)
Organometallics
First Page
199
Last Page
206
Recommended Citation
Huang, D., Vinyard, D., Blakemore, J., Hashmi, S., & Crabtree, R. (2017). Cp∗ versus Bis-carbonyl iridium precursors as CH oxidation precatalysts. Organometallics, 36 (1), 199-206. https://doi.org/10.1021/acs.organomet.6b00525