Vibrationally Hot and Cold Triplets. Sensitizer-Dependent Dynamics and Localized Vibrational Promotion of a Di-π-methane Rearrangement

Kuan, Kai-Yuan; Singleton, Daniel A.

doi:10.1021/jacs.0c10468

Cited by 10 publications

(9 citation statements)

References 36 publications

(28 reference statements)

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“…Very recently, the Singleton group adopted their previously developed high-precision 12 C/ 13 C KIE methodology at natural abundance to experimentally measure the 13 C KIE in this rearrangement of benzobarrelene ( 6 ) at 200 and 300 K using three sensitizers (Figure d) . Remarkably, they observed a significant nominal 13 C KIE (1.138) with an acetophenone sensitizer at 200 K that supported our predicted excited-state heavy-atom tunneling in this rearrangement.…”

Section: Construction Of C–c Bondssupporting

confidence: 69%

New Insights and Predictions into Complex Homogeneous Reactions Enabled by Computational Chemistry in Synergy with Experiments: Isotopes and Mechanisms

Lan

Yang

et al. 2022

Acc. Chem. Res.

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Conspectus Homogeneous catalysis and biocatalysis have been widely applied in synthetic, medicinal, and energy chemistry as well as synthetic biology. Driven by developments of new computational chemistry methods and better computer hardware, computational chemistry has become an essentially indispensable mechanistic “instrument” to help understand structures and decipher reaction mechanisms in catalysis. In addition, synergy between computational and experimental chemistry deepens our mechanistic understanding, which further promotes the rational design of new catalysts. In this Account, we summarize new or deeper mechanistic insights (including isotope, dispersion, and dynamical effects) into several complex homogeneous reactions from our systematic computational studies along with subsequent experimental studies by different groups. Apart from uncovering new mechanisms in some reactions, a few computational predictions (such as excited-state heavy-atom tunneling, steric-controlled enantioswitching, and a new geminal addition mechanism) based on our mechanistic insights were further verified by ensuing experiments. The Zimmerman group developed a photoinduced triplet di-π-methane rearrangement to form cyclopropane derivatives. Recently, our computational study predicted the first excited-state heavy-atom (carbon) quantum tunneling in one triplet di-π-methane rearrangement, in which the reaction rates and 12C/13C kinetic isotope effects (KIEs) can be enhanced by quantum tunneling at low temperatures. This unprecedented excited-state heavy-atom tunneling in a photoinduced reaction has recently been verified by an experimental 12C/13C KIE study by the Singleton group. Such combined computational and experimental studies should open up opportunities to discover more rare excited-state heavy-atom tunneling in other photoinduced reactions. In addition, we found unexpectedly large secondary KIE values in the five-coordinate Fe(III)-catalyzed hetero-Diels–Alder pathway, even with substantial C–C bond formation, due to the non-negligible equilibrium isotope effect (EIE) derived from altered metal coordination. Therefore, these KIE values cannot reliably reflect transition-state structures for the five-coordinate metal pathway. Furthermore, our density functional theory (DFT) quasi-classical molecular dynamics (MD) simulations demonstrated that the coordination mode and/or spin state of the iron metal as well as an electric field can affect the dynamics of this reaction (e.g., the dynamically stepwise process, the entrance/exit reaction channels). Moreover, we unveiled a new reaction mechanism to account for the uncommon Ru(II)-catalyzed geminal-addition semihydrogenation and hydroboration of silyl alkynes. Our proposed key gem-Ru(II)–carbene intermediates derived from double migrations on the same alkyne carbon were verified by crossover experiments. Additionally, our DFT MD simulations suggested that the first hydrogen migration transition-state structures may directly and quickly form the key gem-Ru–carbene structu...

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Section: Construction Of C–c Bondssupporting

confidence: 69%

New Insights and Predictions into Complex Homogeneous Reactions Enabled by Computational Chemistry in Synergy with Experiments: Isotopes and Mechanisms

Lan

Yang

et al. 2022

Acc. Chem. Res.

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“…This rearrangement is therefore another example of a rare heavy‐atom tunneling reaction. Such reactions have been reviewed by Borden, [34] Karney, [38] and more recently by us, [39] and additional examples have been reported over the last few years [40–47] . Quantum tunneling also explains why all attempts to isolate 3 a and related benzocyclopropenes failed: the narrower tunneling distance and lower barrier heights result in higher tunneling probabilities which diminish the lifetimes of the benzocyclopropenes.…”

Section: Discussionmentioning

confidence: 97%

Heavy‐Atom Tunneling in Bicyclo[4.1.0]hepta‐2,4,6‐trienes

Prado Merini,

Schleif,

Sander

2023

Angewandte Chemie

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Heavy‐atom tunneling limits the lifetime and observability of bicyclo[4.1.0]hepta‐2,4,6‐triene, a key intermediate in the rearrangement of phenylcarbene. Bicyclo[4.1.0]hepta‐2,4,6‐triene had been proposed as the primary intermediate of the rearrangement of phenylcarbene, but despite many efforts evaded its characterization even in cryogenic matrices. By introducing fluorine substituents into the ortho‐positions of the phenyl ring of phenylcarbene, the highly strained cyclopropene 1,5‐difluorobicyclo[4.1.0]hepta‐2,4,6‐triene becomes stable enough to be characterized in argon matrices. However, even at 3 K this cyclopropene is only metastable and rearranges via heavy‐atom tunneling to the corresponding cycloheptatetraene. Calculations suggest that fluorination is necessary to slow down the tunneling rearrangement of the bicycloheptatriene. The parent bicycloheptatriene rapidly rearranges via heavy‐atom tunneling and therefore cannot be detected under matrix isolation conditions.

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“…In addition, some reactions involving rare heavy-atom (mostly carbon) tunneling have been experimentally observed or computationally predicted for various systems, including π-bond-shift, Cope-rearrangement, spin-crossover, biosynthesis, and nucleophilic-substitution (S N 2) reactions, as well as carbon-flipping on a Cu(110) surface and excited-state Zimmerman di-π-methane (DPM) rearrangement (Schemes d,e, and S2). − Our previous computational study predicted the first excited-state heavy-atom tunneling in the DPM rearrangement, which was recently supported by Singleton using his natural abundant 13 C NMR experimental method. − In addition, carbon- and nitrogen-tunneling can compete to form different products via two ring-opening pathways of a benzazirine. , Moreover, temperature, solvent, isotope or Lewis-acid was also reported to control the tunneling-involving reactions. , These studies show that several factors (“stimuli”) can affect quantum tunneling in some reactions.…”

mentioning

confidence: 82%

“…In this work, we used reliable density functional theory (DFT) and high-level DLPNO–CCSD(T1) methods in combination with reliable variational transition state theory (VTST) and multidimensional small-curvature tunneling (SCT) correction methods to extensively examine the combined effect of QT and a modest EEF (up to 2.57–5.14 V/nm) on three different reactions (Scheme c–e; computational details are given in the Supporting Information). ,− ,,− These three reactions involve hydrogen- or (ground- and excited-state) carbon-tunneling. Our study shows that an oriented EEF can significantly increase or decrease the rate constants for these reactions at low temperatures.…”

mentioning

confidence: 99%

Quantum Tunneling in Reactions Modulated by External Electric Fields: Reactivity and Selectivity

Zhu

et al. 2023

J. Phys. Chem. Lett.

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Quantum tunneling and external electric fields (EEFs) can promote some reactions. However, the synergetic effect of an EEF on a tunneling-involving reaction and its temperature-dependence is not very clear. In this study, we extensively investigated how EEFs affect three reactions that involve hydrogen-or (ground-and excited-state) carbon-tunneling using reliable DFT, DLPNO−CCSD(T1), and variational transition-state theory methods. Our study revealed that oriented EEFs can significantly reduce the barrier and corresponding barrier width (and vice versa) through more electrostatic stabilization in transition states. These EEF effects enhance the nontunneling and tunneling-involving rates. Such EEF effects also decrease the crossover temperatures and quantum tunneling contribution, albeit with lower and thinner barriers. Moreover, EEFs can modulate and switch on/off the tunnelingdriven 1,2-H migration of hydroxycarbenes under cryogenic conditions. Furthermore, our study predicts for the first time that EEF/tunneling synergy can control the chemo-or siteselectivity of one molecule bearing two similar/same reactive sites.

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Vibrationally Hot and Cold Triplets. Sensitizer-Dependent Dynamics and Localized Vibrational Promotion of a Di-π-methane Rearrangement

Cited by 10 publications

References 36 publications

New Insights and Predictions into Complex Homogeneous Reactions Enabled by Computational Chemistry in Synergy with Experiments: Isotopes and Mechanisms

New Insights and Predictions into Complex Homogeneous Reactions Enabled by Computational Chemistry in Synergy with Experiments: Isotopes and Mechanisms

Heavy‐Atom Tunneling in Bicyclo[4.1.0]hepta‐2,4,6‐trienes

Quantum Tunneling in Reactions Modulated by External Electric Fields: Reactivity and Selectivity

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