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Cp* versus Bis-carbonyl Iridium Precursors as CH Oxidation Precatalysts

Journal Article · · Organometallics
 [1];  [1];  [2];  [3];  [1]
  1. Yale Univ., New Haven, CT (United States). Dept. of Chemistry
  2. Yale Univ., New Haven, CT (United States). Dept. of Chemistry; Univ. of Kansas, Lawrence, KS (United States). Dept. of Chemistry
  3. Yale Univ., New Haven, CT (United States). Dept. of Chemical and Environmental Engineering
+ Show Author Affiliations
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 high-valent 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.
Research Organization:
Energy Frontier Research Centers (EFRC) (United States). Center for Catalytic Hydrocarbon Functionalization (CCHF)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Grant/Contract Number:
SC0001298
OSTI ID:
1397175
Journal Information:
Organometallics, Journal Name: Organometallics Journal Issue: 1 Vol. 36; ISSN 0276-7333
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English

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