Reversible Encapsulation of Xenon and CH<sub>2</sub>Cl<sub>2</sub> in a Solid‐State Molecular Organometallic Framework (Guest@SMOM)

Martínez‐Martínez, Antonio J.; Rees, Nicholas H.; Weller, Andrew S.

doi:10.1002/ange.201910539

Cited by 3 publications

(2 citation statements)

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“…This is consistent with the H2 accessing the active site at higher temperatures, but not at low temperatures. This observation is reminiscent of work by Weller et al, 37 on Rh based MOFs where Xe gas was found to diffuse away from the active site and reside in hydrophobic pockets, similar to enzymatic gas channels. Further, although the formation of the ion pair clearly showed that H2 had entered the solid at room temperature, our TPD measurements did not detect H2 diffusing out of the lattice after freezing the sample to 77 K and evacuating the surrounding gas.…”

Section: Discussionsupporting

confidence: 68%

Heterolytic Scission of Hydrogen Within a Crystalline Frustrated Lewis Pair

et al. 2020

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We report the heterolysis of molecular hydrogen under ambient conditions by the crystalline frustrated Lewis pair (FLP) 1-{2-[bis(pentafluorophenyl)boryl]phenyl}-2,2,6,6tetramethylpiperidine (KCAT). The gas-solid reaction provides an approach to prepare the solvent-free, polycrystalline ion pair KCATH2 through a single crystal to single crystal transformation. The crystal lattice of KCATH2 increases in size relative to the parent KCAT by approximately 2%. Microscopy was used to follow the transformation of the highly colored red/orange KCAT to the colorless KCATH2 over a period of 2 hours at 300 K under a flow of H2 gas. There is no evidence of crystal decrepitation during hydrogen uptake. Inelastic neutron scattering employed over a temperature range from 4 -200 K did not provide evidence for the formation of polarized H2 in a pre-cursor complex within the crystal at low temperatures and high pressures. However, at 300 K the INS spectrum of KCAT transformed to the INS spectrum of KCATH2. Computational methods suggest that the driving force is more favorable in the solid state compared to the solution or gas phase, but the addition of H2 into the KCAT crystal is unfavorable. Ab Initio methods were used to calculate the INS spectra of KCAT, KCATH2 and a possible precursor complex of H2 in the pocket between the B and N of crystalline KCAT. Ex-situ NMR showed that the transformation from KCAT to KCATH2 is quantitative and our results suggest that the hydrogen heterolysis process occurs via H2 diffusion into the FLP crystal with a rate-limiting movement of H2 from inactive positions to reactive sites.

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Section: Discussionsupporting

confidence: 68%

Heterolytic Scission of Hydrogen Within a Crystalline Frustrated Lewis Pair

et al. 2020

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“…Variations of the anion, [19,20] chelating phosphine [15,17,21,22] and extension to a paramagnetic Co‐NBA complex [23] have also been reported. The CF 3 ‐groups in the [BAr F 4 ] − anions are also suggested to play an important role in the ingress of gaseous reactants, and the egress of products, through the crystalline lattice, by providing hydrophobic non‐porous channels [24] …”

Section: Introductionmentioning

confidence: 99%

Solid‐State Confinement Effects in Selective exo‐H/D Exchange in the Rhodium σ‐Norbornane Complex [(Cy₂PCH₂CH₂PCy₂)Rh(η²:η²‐C₇H₁₂)][BAr^F₄]

Macgregor

Krämer

Chadwick

et al. 2023

Helvetica Chimica Acta

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Density functional theory calculations modelling selective exo‐H/D exchange observed in the Rh σ‐alkane complex [(Cy2PCH2CH2PCy2)Rh(η2:η2‐endo‐NBA)][BArF4], [1‐NBA][BArF4], are reported, where ArF=3,5‐C6H3(CF3)2 and NBA=norbornane, C7H12. Two models were considered 1) an isolated molecular cation, [1‐NBA]+ and 2) a full model in which [1‐NBA][BArF4] is treated in the solid state through periodic DFT. After an initial endo‐exo rearrangement, both models predict H/D exchange to proceed through D2 addition and oxidative cleavage followed by a rate‐limiting C−H activation of the norbornane through a σ‐CAM step to form a [1‐Rh(D)(η2‐HD)(norbornyl)]+ intermediate. HD rotation followed by a σ‐CAM C−D bond formation, HD reductive coupling and HD loss then complete the H/D exchange process. exo‐H/D exchange is facilitated by a supporting agostic interaction and is consistently more accessible kinetically than the potentially competing endo‐H/D exchange (isolated cation: ΔG≠exo=+15.9 kcal/mol, ΔG≠endo=+18.4 kcal/mol; solid state: ΔG≠exo=+22.1 kcal/mol, ΔG≠endo=+25.1 kcal/mol). The solid‐state environment has a significant impact on the computed energetics, with barriers increasing by ca. 7 kcal/mol, while only the solid‐state model correctly predicts the endo‐bound NBA complex to be the resting state of the system. These outcomes reflect solid‐state confinement effects within the pocket occupied by the [1‐NBA]+ cation and defined by the pseudo‐octahedral array of neighbouring [BArF4]− anions. The asymmetry of the solid‐state environment also requires a second H/D exchange pathway to be defined to account for reaction at all four exo‐C−H bonds. These entail slightly higher barriers (ΔG≠exo= +24.8 kcal/mol, ΔG≠endo=+27.5 kcal/mol) but retain a distinct preference for exo‐ over endo‐H/D exchange.

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Selectivity of Rh⋅⋅⋅H−C Binding in a σ‐Alkane Complex Controlled by the Secondary Microenvironment in the Solid State

Furfari

Tegner

Burnage

et al. 2021

Chemistry A European J

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Single‐crystal to single‐crystal solid‐state molecular organometallic (SMOM) techniques are used for the synthesis and structural characterization of the σ‐alkane complex [Rh(tBu2PCH2CH2CH2PtBu2)(η2,η2‐C7H12)][BArF4] (ArF=3,5‐(CF3)2C6H3), in which the alkane (norbornane) binds through two exo‐C−H⋅⋅⋅Rh interactions. In contrast, the bis‐cyclohexyl phosphine analogue shows endo‐alkane binding. A comparison of the two systems, supported by periodic DFT calculations, NCI plots and Hirshfeld surface analyses, traces this different regioselectivity to subtle changes in the local microenvironment surrounding the alkane ligand. A tertiary periodic structure supporting a secondary microenvironment that controls binding at the metal site has parallels with enzymes. The new σ‐alkane complex is also a catalyst for solid/gas 1‐butene isomerization, and catalyst resting states are identified for this.

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Reversible Encapsulation of Xenon and CH₂Cl₂ in a Solid‐State Molecular Organometallic Framework (Guest@SMOM)

Cited by 3 publications

References 50 publications

Heterolytic Scission of Hydrogen Within a Crystalline Frustrated Lewis Pair

Heterolytic Scission of Hydrogen Within a Crystalline Frustrated Lewis Pair

Solid‐State Confinement Effects in Selective exo‐H/D Exchange in the Rhodium σ‐Norbornane Complex [(Cy₂PCH₂CH₂PCy₂)Rh(η²:η²‐C₇H₁₂)][BAr^F₄]

Selectivity of Rh⋅⋅⋅H−C Binding in a σ‐Alkane Complex Controlled by the Secondary Microenvironment in the Solid State

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Reversible Encapsulation of Xenon and CH2Cl2 in a Solid‐State Molecular Organometallic Framework (Guest@SMOM)

Cited by 3 publications

References 50 publications

Heterolytic Scission of Hydrogen Within a Crystalline Frustrated Lewis Pair

Heterolytic Scission of Hydrogen Within a Crystalline Frustrated Lewis Pair

Solid‐State Confinement Effects in Selective exo‐H/D Exchange in the Rhodium σ‐Norbornane Complex [(Cy2PCH2CH2PCy2)Rh(η2:η2‐C7H12)][BArF4]

Selectivity of Rh⋅⋅⋅H−C Binding in a σ‐Alkane Complex Controlled by the Secondary Microenvironment in the Solid State

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Reversible Encapsulation of Xenon and CH₂Cl₂ in a Solid‐State Molecular Organometallic Framework (Guest@SMOM)

Solid‐State Confinement Effects in Selective exo‐H/D Exchange in the Rhodium σ‐Norbornane Complex [(Cy₂PCH₂CH₂PCy₂)Rh(η²:η²‐C₇H₁₂)][BAr^F₄]