Publicación:
New Ir Bis-Carbonyl Precursor for Water Oxidation Catalysis

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Fecha
2016
Autores
Carpio, JA
Gago, AM
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ACS Publications
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Abstracto
This paper introduces IrI(CO)2(pyalc) (pyalc = (2-pyridyl)-2-propanoate) as an atom-efficient precursor for Ir-based homogeneous oxidation catalysis. This compound was chosen to simplify analysis of the water oxidation catalyst species formed by the previously reported Cp*IrIII(pyalc)OH water oxidation precatalyst. Here, we present a comparative study on the chemical and catalytic properties of these two precursors. Previous studies show that oxidative activation of Cp*Ir-based precursors with NaIO4 results in formation of a blue IrIV species. This activation is concomitant with the loss of the placeholder Cp* ligand which oxidatively degrades to form acetic acid, iodate, and other obligatory byproducts. The activation process requires substantial amounts of primary oxidant, and the degradation products complicate analysis of the resulting IrIV species. The species formed from oxidation of the Ir(CO)2(pyalc) precursor, on the other hand, lacks these degradation products (the CO ligands are easily lost upon oxidation) which allows for more detailed examination of the resulting Ir(pyalc) active species both catalytically and spectroscopically, although complete structural analysis is still elusive. Once Ir(CO)2(pyalc) is activated, the system requires acetic acid or acetate to prevent the formation of nanoparticles. Investigation of the activated bis-carbonyl complex also suggests several Ir(pyalc) isomers may exist in solution. By 1H NMR, activated Ir(CO)2(pyalc) has fewer isomers than activated Cp*Ir complexes, allowing for advanced characterization. Future research in this direction is expected to contribute to a better structural understanding of the active species. A diol crystallization agent was needed for the structure determination of 3.
Descripción
This research was supported by the Center for Catalytic Hydrocarbon Functionalization, Number DE-SC0001298 (D.L.H. and R.H.C.), and Argonne-Northwestern Solar Energy Research (ANSER), Number DE-SC0001059 (J.M.T., R.-B.S., K.L.M. and G.W.B.); both agencies are Energy Frontier Research Centers funded by the U.S. Department of Energy. D.L.H acknowledges support by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-1122492 and the Yale Dox Summer Research Fellowship. R.-B.S. R. B.-S. acknowledges support from the Consejo Nacional de Ciencia, Tecnologia e Innovacio ́ ́n Tecnologica (CONCYTEC), and the Ponti ́ ficia Universidad Catolica del Peru ́ ́(PUCP). DLS measurements were conducted in the Yale Facility for Light Scattering. We thank Liam Sharninghausen for assistance with crystallography and Dr. Eric Paulson for assistance with DOSY NMR spectroscopy.
Palabras clave
water oxidation catalyst, atom-efficient precursor, oxidation catalysis
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