Mononuclear Iridium Dinitrogen Complexes Bonded to Zeolite HY

Yang, Dong; Chen, Mingyang; Martínez-Macias, Claudia; Dixon, David A.; Gates, Bruce C.

doi:10.1002/chem.201404794

Cited by 12 publications

(19 citation statements)

References 47 publications

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“…Elucidation of this reaction network was made possible by replacement of one of the carbonyl ligands on iridium with an alkene, which was then replaced by hydrogen. DFT calculations of zeolite‐supported complexes for two models, an Al(OH) 4 model of the acid site and a larger model, Zeo(48‐T),26 show that the order of ligand dissociation energies for removal of the first ligand from iridium follows the trend CO>C 2 H 4 >H 2 (Table 5), matching our experimental results. The IrCO bond has the highest dissociation energy, so that when the sample is treated with flowing ethylene, it is possible to remove only a single carbonyl ligand, followed by the replacement of the ethylene with hydrogen.…”

Section: Discussionsupporting

confidence: 82%

“…All of the calculations were done by using the Gaussian 03/09 program suites 32. Calculations for several more complex models of comparable supported iridium species have also been reported,26 confirming the appropriateness of the choice of the simplified model for the comparisons with experiment reported here. The Zeo(48‐T) model is a relatively realistic model obtained by truncating the zeolite crystal structure, and it was used to test the small Al(OH) 4 model.…”

Section: Experimental and Computational Sectionsupporting

confidence: 65%

“…Computational Methods : Two models of the zeolite were used for the calculations. A simple model of the zeolite surface site, represented as ML n Al(OH) 4 , (where M is Ir and L represents the ligands), was chosen because earlier work showed that it provides good agreement with the structural and vibrational frequency measurements determined by experiment for analogous rhodium complexes,28 as well as for N 2 complexes when compared with experiment and with larger models of the acidic zeolite site 26. Geometry optimization and second‐derivative frequency calculations of the supported iridium complexes for this model were carried out by using DFT with the B3LYP exchange‐correlation functional,29, 30 the aug‐cc‐pVDZ basis set31 on H, C, N, O, and Al, and the aug‐cc‐pVDZ‐pp basis set and pseudopotential31 on iridium.…”

Section: Experimental and Computational Sectionmentioning

confidence: 99%

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Single‐Site Zeolite‐Anchored Organoiridium Carbonyl Complexes: Characterization of Structure and Reactivity by Spectroscopy and Computational Chemistry

Martínez-Macias

Chen

Dixon

et al. 2015

Chemistry A European J

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A family of HY zeolite-supported cationic organoiridium carbonyl complexes was formed by reaction of Ir(CO)2(acac) (acac = acetylacetonate) to form supported Ir(CO)2 complexes, which were treated at 298 K and 1 atm with flowing gas-phase reactants, including C2H4, H2, 12 CO, 13 CO, and D2O. Mass spectrometry was used to identify effluent gases, and infrared and X-ray absorption spectroscopies were used to characterize the supported species, with the results bolstered by DFT calculations. Because the support is crystalline and presents a nearly uniform array of bonding sites for the iridium species, these were characterized by a high degree of uniformity, which allowed a precise determination of the species involved in the replacement, for example, of one CO ligand of each Ir(CO)2 complex with ethylene. The supported species include the following: Ir(CO)2, Ir(CO)(C2H4)2, Ir(CO)(C2H4), Ir(CO)(C2H5), and (tentatively) Ir(CO)(H). The data determine a reaction network involving all of these species.

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Section: Discussionsupporting

confidence: 82%

Section: Experimental and Computational Sectionsupporting

confidence: 65%

Section: Experimental and Computational Sectionmentioning

confidence: 99%

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Single‐Site Zeolite‐Anchored Organoiridium Carbonyl Complexes: Characterization of Structure and Reactivity by Spectroscopy and Computational Chemistry

Martínez-Macias

Chen

Dixon

et al. 2015

Chemistry A European J

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“…[43] All calculations were done with the hybrid B3LYP exchange-correlation functional, [44][45][46] at the Douglas-Kroll-Hess second order scalar relativistic level [46][47][48] using geometries de-termined in our prior work. [29,30,49] Polarized double-z-DK basis sets were used. [50,51] FEFF and DOS modeling:H ERFD XANES spectra were simulated by use of the FEFF 9.7 code.…”

Section: Methodsmentioning

confidence: 99%

High‐Energy‐Resolution X‐ray Absorption Spectroscopy for Identification of Reactive Surface Species on Supported Single‐Site Iridium Catalysts

Hoffman

Sokaras

Zhang

et al. 2017

Chemistry A European J

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What is the most significant result of this study?The ability to identify adsorbed intermediates in ac atalytic reaction is of paramount importance to furthering our understanding of catalytic processes. Infrared spectroscopy is often the technique of choice, but it has limitations concerning sensitivity.U sing highenergy resolution fluorescence detection (HERFD) X-ray absorption spectroscopy (XAS) we have been able to demonstrate that there are unique features in the spectra that can be assigned to specific ligands bound to ac atalytic iridium center.H ERFD-XAS is thus expected to have an increasing role in catalysis research by facilitating the determination of mechanisms of solid-catalyzed reactions through identification of reaction intermediates in working catalysts How would you describe to the layperson the most significant result of this study?We are using synchrotron light sources to probe catalysts, materials that speed up chemical reactions so they use less energy and produce less waste, at the molecular level to discover how they work so that we can improve them. What was the inspiration for this cover design?Any time you are invited to submit cover art there is the excitement in brainstorming ideas that portray the science in am eaningful but visual and striking way.F or this cover,w ew anted to summarize the key conclusion in as ingle image-the need for as ynchrotron like SSRL to provide X-ray photons of sufficienti ntensity, the structure of the catalyst that was actually probed, the spectrometer,a nd the resulting X-ray absorption spectrum. The resulting image nicely captures all of these elements. Who contributed to the idea behind the cover?Primarily Simon Bare and Adam Hoffmanw orking with the graphic artist Gregory Stewart at SLAC National Accelerator Laboratory What other topicsare you working on at the moment?Motivateda nd excited by this work, we are nowe xtendingt he application of HERFD-XAS to probet he electronic environmento ft he metalc enter in more challenging catalysts ystems. Thesei nclude,catalystsw ithe xtremely low metal loading (< 0.005 wt%m etal), ionic liquidm odified catalysts, ands tructureo ft he actual working catalyst in isolateds ingle site iridium catalysts under ethylene hydrogenation conditions. Each of these experiments brings new challengesa nd has thep otentialt oe xpandour understandingo fs uch catalysts.

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“…The vibrational spectra are accounted for by the metal atom and the ligand atoms immediately bonded to it; the rest of the zeolite does not strongly influence these spectra [16,17]. The ligand dissociation energies (LDEs) are more strongly influenced by the size of the model representing the zeolite, depending on whether the zeolite framework rearranges when ligands are removed to fill the vacant site and stabilize the product to reduce the LDE [18,19]. An issue with all such calculations is the need to properly identify the spin state of the active metal site and to be aware that spin crossings may occur.…”

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confidence: 99%