High‐Valent Metal–Oxo Species at the Nodes of Metal–Triazolate Frameworks: The Effects of Ligand Exchange and Two‐State Reactivity for C−H Bond Activation

Rosen, Andrew; Notestein, Justin M.; Snurr, Randall Q.

doi:10.1002/ange.202004458

Cited by 13 publications

(14 citation statements)

References 95 publications

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“…Cr(III) has a lower Pauling electronegativity (1.66) than Fe(III) (1.83), which enhances radical stabilization on Cr(III) sites. Lower enthalpies of formation for high valent oxo formation are calculated for Cr(III) than for Fe(III) in weak ligand fields, indicating more energetically facile oxo formation for the former. It is well established that high valent transition metal oxo species are capable of abstracting strong C–H and O–H bonds, and in this case, H-abstraction from styrene (or other species) prior to metallocycle formation results in a metal-bound intermediate of the form O-R with R as H or OH.…”

Section: Resultsmentioning

confidence: 87%

Mechanistic Impacts of Metal Site and Solvent Identities for Alkene Oxidation over Carboxylate Fe and Cr Metal–Organic Frameworks

Yang

Sarazen

2022

ACS Catal.

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Isolated Fe(III) and Cr(III) sites contained in nanoporous voids of isoreticular carboxylate MIL-101(Fe) and MIL-101(Cr) are interrogated for their reactivity and selectivity of liquid-phase styrene oxidation by hydrogen peroxide (H 2 O 2 ). Batch kinetic measurements in acetonitrile (MeCN) at 323 K showcase that both metal-normalized oxygenate production and H 2 O 2 consumption rates are O(10 1 ) higher for MIL-101(Fe) than MIL-101(Cr). Thermodynamically consistent reaction pathways, constructed through spiking experiments, reveal complex interconnectivities between primary (styrene oxide, benzaldehyde) and secondary (styrene glycol, benzoic acid, phenylacetaldehyde) oxygenates. Though benzaldehyde is the majority product for both MIL-101(Fe) and MIL-101(Cr), isoconversion (X styrene = 7%) product distributions suggest intrinsic differences in preferred reaction pathways. Apparent energy barriers for all pathways are lower over MIL-101(Fe) than for MIL-101(Cr), conferred by metal electron affinity differences for primary oxygenate selectivity, while secondary (inter)conversion rates trend with acid site densities. Fitted rate laws, radical trapping, adsorption experiments, and complementary DFT calculations indicate surface-mediated reactions by H 2 O 2 -derived surface species that outcompete bound styrene, product oxygenate, solvent, and water molecules for both MIL-101(Fe) and MIL-101(Cr) in MeCN. Extracted enthalpic and entropic effects from temperature-dependent experiments (318−328 K) in MeCN and MeOH showcase the ability of hydrogen bonding solvents in locally hydrophilic environments to selectively stabilize primary oxygenate transition states and indicate additional confinement effects from microporous substructures in MIL-101(Fe) and . Simplified rate expressions are expanded to encompass first-order catalyst deactivation rates through temporal metal leaching experiments and assert that metal leaching dominates MIL-101(Cr) catalyst inefficiencies, while a combination of metal leaching and other (ir)reversible site changes are present for MIL-101(Fe). Overall, this work combines kinetic, spectroscopic, numerical, and computational approaches to rigorously define reaction and deactivation mechanisms for styrene oxidation by H 2 O 2 over isoreticular MIL-101(Fe) and MIL-101(Cr).

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Section: Resultsmentioning

confidence: 87%

Mechanistic Impacts of Metal Site and Solvent Identities for Alkene Oxidation over Carboxylate Fe and Cr Metal–Organic Frameworks

Yang

Sarazen

2022

ACS Catal.

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“… 36 − 41 Instead, first-principles computation with density functional theory (DFT) has filled this gap 42 − 46 in understanding the electronic structure 47 − 50 needed for C–H bond activation. First-principles modeling has revealed the role of spin state in reactivity 51 − 55 and the importance of multistate reactivity 56 − 59 that is difficult to study experimentally. 60 To reduce the computational cost of catalyst screening needed to explore a large chemical space, it is appealing to extend to homogeneous catalysis 61 , 62 linear free energy relationships (LFERs) 29 , 63 − 67 between thermodynamic steps or Brønsted–Evans–Polanyi (BEP) 68 − 71 relationships between barrier heights and reaction energies.…”

Section: Introductionmentioning

confidence: 99%

“…Compounding the challenges of the need to search a large space, high-valent metal-oxo moieties that are frequently invoked for C–H bond activation in transition-metal complexes, ,− heterogeneous catalysts, − or enzymes ,, are challenging to isolate and characterize experimentally. − Instead, first-principles computation with density functional theory (DFT) has filled this gap − in understanding the electronic structure − needed for C–H bond activation. First-principles modeling has revealed the role of spin state in reactivity − and the importance of multistate reactivity − that is difficult to study experimentally . To reduce the computational cost of catalyst screening needed to explore a large chemical space, it is appealing to extend to homogeneous catalysis , linear free energy relationships (LFERs) ,− between thermodynamic steps or Brønsted–Evans–Polanyi (BEP) − relationships between barrier heights and reaction energies.…”

Section: Introductionmentioning

confidence: 99%

New Strategies for Direct Methane-to-Methanol Conversion from Active Learning Exploration of 16 Million Catalysts

Nandy

Duan

Conrad

et al. 2022

JACS Au

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Despite decades of effort, no earth-abundant homogeneous catalysts have been discovered that can selectively oxidize methane to methanol. We exploit active learning to simultaneously optimize methane activation and methanol release calculated with machine learning-accelerated density functional theory in a space of 16 M candidate catalysts including novel macrocycles. By constructing macrocycles from fragments inspired by synthesized compounds, we ensure synthetic realism in our computational search. Our large-scale search reveals that low-spin Fe(II) compounds paired with strong-field (e.g., P or S-coordinating) ligands have among the best energetic tradeoffs between hydrogen atom transfer (HAT) and methanol release. This observation contrasts with prior efforts that have focused on high-spin Fe(II) with weak-field ligands. By decoupling equatorial and axial ligand effects, we determine that negatively charged axial ligands are critical for more rapid release of methanol and that higher-valency metals [i.e., M(III) vs M(II)] are likely to be rate-limited by slow methanol release. With full characterization of barrier heights, we confirm that optimizing for HAT does not lead to large oxo formation barriers. Energetic span analysis reveals designs for an intermediate-spin Mn(II) catalyst and a low-spin Fe(II) catalyst that are predicted to have good turnover frequencies. Our active learning approach to optimize two distinct reaction energies with efficient global optimization is expected to be beneficial for the search of large catalyst spaces where no prior designs have been identified and where linear scaling relationships between reaction energies or barriers may be limited or unknown.

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“…In light of these findings, the relative energy of M-O intermediate species was proposed as a descriptor to assess the NO oxidation catalytic activity of a metal oxo-trimer. It is worth noting that the M-O binding strength of O 2 adsorbed on metal sites has been recently discussed in the context of C–H bond activation by MOFs. − …”

mentioning

confidence: 99%

Mechanistic Insight into the Catalytic NO Oxidation by the MIL-100 MOF Platform: Toward the Prediction of More Efficient Catalysts

Lyu

Maurin

2020

ACS Catal.

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Through density functional theory calculations, we unravel a microscopic picture of the catalytic NO oxidation activity of the MIL-100 MOF platform. By systematically varying the nature of the coordinatively unsaturated metal sites (Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Ru), we demonstrate the relative energy of the metal–oxygen intermediate species to be a reliable descriptor to anticipate the catalytic activity of this family of MOFs. These conclusions are first validated by experimental data on MIL-100(Fe)/MIL-100(Fe,Mn) and further used as guidelines to develop a ruthenium-based MIL-100 with even better catalytic performance.

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High‐Valent Metal–Oxo Species at the Nodes of Metal–Triazolate Frameworks: The Effects of Ligand Exchange and Two‐State Reactivity for C−H Bond Activation

Cited by 13 publications

References 95 publications

Mechanistic Impacts of Metal Site and Solvent Identities for Alkene Oxidation over Carboxylate Fe and Cr Metal–Organic Frameworks

Mechanistic Impacts of Metal Site and Solvent Identities for Alkene Oxidation over Carboxylate Fe and Cr Metal–Organic Frameworks

New Strategies for Direct Methane-to-Methanol Conversion from Active Learning Exploration of 16 Million Catalysts

Mechanistic Insight into the Catalytic NO Oxidation by the MIL-100 MOF Platform: Toward the Prediction of More Efficient Catalysts

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