Iridium(I)/N‐Heterocyclic Carbene Hybrid Materials: Surface Stabilization of Low‐Valent Iridium Species for High Catalytic Hydrogenation Performance

Romanenko, Iuliia; Gajan, David; Sayah, Reine; Crozet, Delphine; Jeanneau, Erwan; Lucas, C. Robert; Leroux, Lénaic; Veyre, Laurent; Lesage, Anne; Emsley, Lyndon; Lacôte, Emmanuel; Thieuleux, Chloé

doi:10.1002/anie.201505867

Cited by 39 publications

(47 citation statements)

References 47 publications

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“…DNP has been used to characterize mesoporous silica functionalized by organic species (see Figure 1c) [36,102,122,208,228,232,252,253] or metal complexes [134,236,[254][255][256][257][258][259][260] as well as encapsulating metal nanoparticles [261]. The sensitivity provided by DNP is particularly useful for the detection of surface sites, notably when they are occupied by insensitive nuclei, such as 15 [222,262].…”

Section: Mesoporous Materialsmentioning

confidence: 99%

Recent developments in MAS DNP-NMR of materials

Rankin

Trébosc

Pourpoint

et al. 2019

Solid State Nuclear Magnetic Resonance

146

137

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Solid-state NMR spectroscopy is a powerful technique for the characterization of the atomic-level structure and dynamics of materials. Nevertheless, the use of this technique is often limited by its lack of sensitivity, which can prevent the observation of surfaces, defects or insensitive isotopes. Dynamic Nuclear Polarization (DNP) has been shown to improve by one to three orders of magnitude the sensitivity of NMR experiments on materials under Magic-Angle Spinning (MAS), at static magnetic field B0 ≥ 5 T, conditions allowing for the acquisition of high-resolution spectra. The field of DNP-NMR spectroscopy of materials has undergone a rapid development in the last ten years, spurred notably by the availability of commercial DNP-NMR systems. We provide here an in-depth overview of MAS DNP-NMR studies of materials at high B0 field. After a historical perspective of DNP of materials, we describe the DNP transfers under MAS, the transport of polarization by spin diffusion and the various contributions to the overall sensitivity of DNP-NMR experiments. We discuss the design of tailored polarizing agents and the sample preparation in the case of materials. We present the DNP-NMR hardware and the influence of key experimental parameters, such as microwave power, magnetic field, temperature and MAS frequency. We give an overview of the isotopes, which have been detected by this technique, and the NMR methods, which have been combined with DNP. Finally, we show how MAS DNP-NMR has been applied to gain new insights into the structure of organic, hybrid and inorganic materials with applications in fields, such as health, energy, catalysis, optoelectronics etc.

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Section: Mesoporous Materialsmentioning

confidence: 99%

Recent developments in MAS DNP-NMR of materials

Rankin

Trébosc

Pourpoint

et al. 2019

Solid State Nuclear Magnetic Resonance

146

137

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“…Organometallic complexes are widely used in chemistry, both in academic research and in industry, ranging from hydrogenation and polymerization reactions, to the production of fine chemicals and semiconductors. [1][2][3][4][5][6][7][8][9][10] However, characterisation of these complexes and the il-lumination of their reaction pathways remains challenging. [11][12] This is not surprizing because transformations of organometallic complexes in solution often involve the formation of short-lived reaction intermediates present in low concentrations and, therefore, inaccessible to commonly used detection techniques, such as nuclear magnetic resonance (NMR) spectroscopy.…”

Section: Supporting Information Placeholdermentioning

confidence: 99%

Indirect Detection of Short-lived Hydride Intermediates of Iridium N-Heterocyclic Carbene Complexes via Chemical Exchange Saturation Transfer (CEST) Spectroscopy

Knecht¹,

Hadjiali²,

Barskiy³

et al. 2019

Preprint

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For the first time chemical-exchange saturation transfer (CEST) 1H NMR is utilized for the study of short-lived hydride intermediates in the catalytic cycle of the Iridium-based organometallic complex [Ir(IMes)(Py)3(H)2]Cl, which are often not observable by other NMR techniques, since they are low concentrated, and undergo reversible ligand exchange with the main complex. The intermediate complexes [Ir(Cl)(IMes)(Py)2(H)2] and [Ir(CD3OD)(IMes) (Py)2(H)2] are detected, assigned and characterized in situ and at room temperature in solution. Understanding the effects on the spin dynamics induced by these complexes is necessary for enhancing the performance of the nuclear spin hyperpolarization technique SABRE (Signal Amplification By Reversible Exchange). By eliminating [Ir(Cl)(IMes)(Py)2(H)2] and manipulating the spin-system by RF-irradiation, we were able to increase the nuclear spin singlet lifetime of the two protons in the main hydride complex by more than an order of magnitude, from 2.2±0.1 s to 27.2±1.2 s. The presented CEST NMR approach has a large application potential for studying short-lived hydride intermediates in catalytic reactions.

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“…Besides being a significant improvement in the catalytic activity of this specific class of catalysts, TOFs values of 7.1 and 4.3 s −1 for ethene and propene, respectively, are remarkable absolute values. Overall, 2a cannot compete with grafted complexes of f ‐ or early d ‐elements,[18] but is considerably more active alkene hydrogenation catalysts than other Ir‐ and Rh‐based grafted complexes. Although a quantitative comparison with the heterogeneous hydrogenation of ethene and propene with crystals of related pincer Ir(I) complexes is obviously not possible, the above results suggest a higher activity for the silica‐grafted hydride 2a .…”

Section: Resultsmentioning

confidence: 99%

Batch and Continuous Flow Hydrogenation of Liquid and Gaseous Alkenes Catalyzed by a Silica‐grafted Iridium(III) Hydride

Rimoldi

Mezzetti

2016

Helvetica Chimica Acta

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The silica‐grafted hydride complex [IrH(SBA‐15)(PCP)] (2a; PCP = 1,3‐bis((di‐tert‐butylphosphino)methyl)benzene) hydrogenates alkenes under ambient condition without prior activation. Compared to its POCOP analogue (POCOP = 1,3‐bis((di‐tert‐butylphosphino)oxy)benzene), the activity of catalyst 2a is significantly improved with liquid substrates and exceptionally boosted with ethene and propene. Under gas flow conditions, catalyst 2a hydrogenates ethene with a remarkable turnover frequency of 0.95 s−1. A stability test indicates that the conversion is constant for at least 1 week.

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Iridium(I)/N‐Heterocyclic Carbene Hybrid Materials: Surface Stabilization of Low‐Valent Iridium Species for High Catalytic Hydrogenation Performance

Cited by 39 publications

References 47 publications

Recent developments in MAS DNP-NMR of materials

Recent developments in MAS DNP-NMR of materials

Indirect Detection of Short-lived Hydride Intermediates of Iridium N-Heterocyclic Carbene Complexes via Chemical Exchange Saturation Transfer (CEST) Spectroscopy

Batch and Continuous Flow Hydrogenation of Liquid and Gaseous Alkenes Catalyzed by a Silica‐grafted Iridium(III) Hydride

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