Synthesis and crystal structure of Ir(C2H4)2(C5H7O2)

Zeolite HSSZ-53, which has 1-dimensional channels with 14-ring extra-large pores, was used as a support for a molecular iridium complex synthesized from Ir(C 2 H 4 ) 2 (C 5 H 7 O 2 ) and characterized with infrared (IR) and extended X-ray absorption fine structure (EXAFS) spectroscopies and atomic-resolution aberration-corrected scanning transmission electron microscopy (STEM). The spectra show that Ir(C 2 H 4 ) 2 (C 5 H 7 O 2 ) reacted readily with the bridging OH groups of the zeolite, leading to the removal of C 5 H 7 O 2 ligands and the formation of mononuclear Ir(C 2 H 4 ) 2 complexes bonded to the zeolite by Ir−O bonds at the framework aluminum sites. STEM images confirm the spectra, showing site-isolated iridium centers within the zeolite channels, with no evidence of iridium clusters. The samples constitute a highly uniform, well-defined array of essentially molecular catalytic species in a highly uniform, confined environment, allowing precise investigations of the chemistry of the iridium complex in the absence of solvents. IR spectra show that the supported Ir(C 2 H 4 ) 2 complexes were converted to Ir(C 2 H 5 ) 2 , Ir(CO) 2 , Ir(CO)(C 2 H 4 ), and Ir(CO)(C 2 H 4 ) 2 as various mixtures of H 2 , CO, and C 2 H 4 reacted with the sample. The sample was tested as a catalyst for ethylene hydrogenation and for H−D exchange in the reaction of H 2 + D 2 . The data, combined with results reported for isostructural iridium complexes bonded to zeolite HY and to MgO, demonstrate how the catalytic activity can be tuned by choice of the support, with the support being characterized as a ligand with electron-donating or electronwithdrawing properties. The results demonstrate that the rate of ethylene hydrogenation catalyzed by the supported iridium complexes is limited by H 2 activation when the iridium is electron rich (on the MgO support), whereas the rate-limiting step is C 2 H 4 adsorption when the iridium is electron deficient (on either zeolite support).

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“…16 This observation indicates that the ethylene ligands remained bonded to the iridium during the chemisorption.…”

Section: ■ Resultsmentioning

confidence: 95%

Site-Isolated Molecular Iridium Complex Catalyst Supported in the 1-Dimensional Channels of Zeolite HSSZ-53: Characterization by Spectroscopy and Aberration-Corrected Scanning Transmission Electron Microscopy

Lu¹,

Aydin²,

Liang

et al. 2012

ACS Catal.

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“…Reference backscattering phase shifts were calculated with the software FEFF7 41 from crystallographic data. [Ir(C 2 H 4 ) 2 (acac)], which has a known crystal structure 30 incorporating π-bonded ethylene ligands and a bidentate acac ligand, was used as the reference for Ir−O support , Ir−C, Ir−O long , and Ir−C long (the latter two being Ir−O and Ir−C contributions at distances longer than bonding distances); Ir−Al alloy 42 (Al 3 Ir) was used for Ir−Al contributions, and iridium metal 42 was used for Ir−Ir first-and second-shell contributions. For a summary of the Ir-backscatterer distances in the reference compounds used for EXAFS analysis, see the Supporting Information, Table SI-2. Iterative fitting was done in R (distance) space with the Fourier-transformed χ data until optimum agreement was attained between the calculated k 0 -, k 1 -, k 2 -, and k 3 -weighted EXAFS data and each postulated model (k is the wave vector).…”

Section: ■ Introductionmentioning

confidence: 99%

“…Hence, the observed decrease in catalytic activity upon addition of P(OCH 3 ) 3 is inferred to have been caused by the addition of P(OCH 3 ) 3 and not any aspect of the ∼1 h procedure required for that addition. 30 was slurried with highly dealuminated zeolite Y (Si/Al atomic ratio = 30) to form [Ir(C 2 H 4 ) 2 ]/zeolite Y. The structure of the supported iridium complex was elucidated on the basis of multiple complementary techniques including EXAFS, IR, and NMR spectroscopies, STEM, mass spectrometry of effluent gases formed during sample treatments, and density functional theory.…”

Section: ■ Introductionmentioning

confidence: 99%

Mononuclear Zeolite-Supported Iridium: Kinetic, Spectroscopic, Electron Microscopic, and Size-Selective Poisoning Evidence for an Atomically Dispersed True Catalyst at 22 °C

Bayram

Aydin

et al. 2012

ACS Catal.

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This work addresses the question of what is the true catalyst when beginning with a site-isolated, atomically dispersed precatalyst for the prototype catalytic reaction of cyclohexene hydrogenation in the presence of cyclohexane solvent: is the atomically dispersed nature of the zeolitesupported, [Ir(C 2 H 4 ) 2 ]/zeolite Y precatalyst retained, or are possible alternatives including Ir 4 subnanometer clusters or larger, Ir(0) n , nanoparticles the actual catalyst? Herein we report the (a) kinetics of the reaction; (b) physical characterizations of the used catalyst, including extended X-ray absorption fine structure spectra plus images obtained by high-angle annular dark-field scanning transmission electron microscopy, demonstrating the mononuclearity and site-isolation of the catalyst; and the (c) results of poisoning experiments, including those with the size-selective poisons P(C 6 H 11 ) 3 and P(OCH 3 ) 3 determining the location of the catalyst in the zeolite pores. Also reported are quantitative poisoning experiments showing that each added P(OCH 3 ) 3 molecule poisons one catalytic site, confirming the single-metal-atom nature of the catalyst and the lack of leaching of catalyst into the reactant solution. The results (i) provide strong evidence that the use of a site-isolated [Ir(C 2 H 4 ) 2 ]/zeolite Y precatalyst allows a site-isolated [Ir 1 ]/zeolite Y hydrogenation catalyst to be retained even when in contact with solution, at least at 22°C; (ii) allow a comparison of the solid− solution catalyst system with the equivalent one used in the solid−gas ethylene hydrogenation reaction at room temperature; and (iii) illustrate a methodology by which multiple, complementary physical methods, combined with kinetic, size-selective poisoning, and quantitative kinetic poisoning experiments, help to identify the catalyst. The results, to our knowledge, are the first identifying an atomically dispersed, supported transition-metal species as the catalyst of a reaction taking place in contact with solution.

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“…It should be noted that the X-ray crystal structure of the closely related complex [Ir(acac)(C 2 H 4 ) 2 ] was reported [22]. The observed bonding parameters of [Ir(acac)(coe) 2 ] agree also well with the reported ones of the latter: Ir-C, 2.107 (2) and Ir-C, 2.108 (3) [Ir(acac)(C 2 H 4 ) 2 ] was prepared from 1 by replacing the coe ligands by ethylene followed by treatment with KOH/Hacac in yields of about 45% related to Ir [22].…”

Section: Crystal and Molecular Structure Ofmentioning

confidence: 99%

[Ir(acac)(η2-C8H14)2]: A precursor in the synthesis of cyclometalated iridium(III) complexes

Böttcher

Graf

Sünkel

et al. 2011

Inorganica Chimica Acta

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Synthesis and crystal structure of Ir(C2H4)2(C5H7O2)

Cited by 40 publications

References 23 publications

Site-Isolated Molecular Iridium Complex Catalyst Supported in the 1-Dimensional Channels of Zeolite HSSZ-53: Characterization by Spectroscopy and Aberration-Corrected Scanning Transmission Electron Microscopy

Site-Isolated Molecular Iridium Complex Catalyst Supported in the 1-Dimensional Channels of Zeolite HSSZ-53: Characterization by Spectroscopy and Aberration-Corrected Scanning Transmission Electron Microscopy

Mononuclear Zeolite-Supported Iridium: Kinetic, Spectroscopic, Electron Microscopic, and Size-Selective Poisoning Evidence for an Atomically Dispersed True Catalyst at 22 °C

[Ir(acac)(η2-C8H14)2]: A precursor in the synthesis of cyclometalated iridium(III) complexes

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