Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 135, Issue 29, Pages 10837-10851Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja4048762
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Funding
- Center for Catalytic Hydrocarbon Functionalization, an Energy Frontier Research Center
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-SC0001298]
- NSF GRFP
- Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the U.S. Department of Energy [DE-FG02-07ER15909]
- Yale Institute for Nanoscience and Quantum Engineering (YINQE)
- Yale Center for Research on Interface Structures and Phenomena (CRISP)
- NSF MRSEC DMR [1119826]
- Alexander von Humboldt Foundation for a Feodor Lynen Research Fellowship
- YINQE
- NSF Graduate Research Fellowships
- U.S. National Science Foundation (Raman spectroscopy) [CHE-1112239]
- Direct For Mathematical & Physical Scien
- Division Of Chemistry [1112239] Funding Source: National Science Foundation
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We present evidence for Cp* being a sacrificial placeholder ligand in the [Cp*Ir-III(chelate)X] series of homogeneous oxidation catalysts. UV-vis and H-1 NMR profiles as well as MALDI-MS data show a rapid and irreversible loss of the Cp* ligand under reaction conditions, which likely proceeds through an intramolecular inner-sphere oxidation pathway reminiscent of the reductive in situ elimination of diolefin placeholder ligands in hydrogenation catalysis by [(diene)M-I(L,L')](+) (M = Rh and Ir) precursors. When oxidatively stable chelate ligands are bound to the iridium in addition to the Cp*, the oxidized precursors yield homogeneous solutions with a characteristic blue color that remain active in both water- and CH-oxidation catalysis without further induction period. Electrophoresis suggests the presence of well-defined Ir-cations, and TEM-EDX, XPS, O-17 NMR, and resonance-Raman spectroscopy data are most consistent with the molecular identity of the blue species to be a bis-mu-oxo di-iridium(IV) coordination compound with two waters and one chelate ligand bound to each metal. DFT calculations give insight into the electronic structure of this catalyst resting state, and time-dependent simulations agree with the assignments of the experimental spectroscopic data. [(cod)Ir-I(chelate)] precursors bearing the same chelate ligands are shown to be equally effective precatalysts for both water- and CH-oxidations using NaIO4 as chemical oxidant.
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