Isotope-Controlled Selectivity by Quantum Tunneling: Hydrogen Migration versus Ring Expansion in Cyclopropylmethylcarbenes

Nandi, Ashim; Gerbig, Dennis; Schreiner, Peter R.; Borden, Weston Thatcher; Kozuch, Sebastian

doi:10.1021/jacs.7b04593

Cited by 27 publications

(31 citation statements)

References 15 publications

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“…[2] Thei ncreasing number of recent reports on experimental and theoretical heavy-atom QMT reactions, however, seems to suggest that this phenomenon occurs more frequently than had been assumed and can have significant implications for many chemical reactions. [31][32][33][34][35][36] One of the first examples of heavy-atom QMT was described by Buchwalter and Closs in 1975, regarding the ring-closure of triplet 1,3-cyclopentanediyl 3 I to bicyclopentane II in cryogenic glasses at 1.3 to 20 K( Scheme 1a). [17] Additional evidence of heavy-atom QMT on the ring-closure of triplet 1,3-diradicals was described later by Dougherty and co-workers for the transformation of triplet 1,3-cyclobutanediyls 3 III to bicyclobutanes IV in cryogenic matrices at 4t o 20 K( Scheme 1b).…”

Section: Introductionmentioning

confidence: 99%

Heavy‐Atom Tunneling Through Crossing Potential Energy Surfaces: Cyclization of a Triplet 2‐Formylarylnitrene to a Singlet 2,1‐Benzisoxazole

et al. 2020

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Not long ago, the occurrence of quantum mechanical tunneling (QMT) chemistry involving atoms heavier than hydrogen was considered unreasonable. Contributing to the shift of this paradigm, we present here the discovery of a new and distinct heavy‐atom QMT reaction. Triplet syn‐2‐formyl‐3‐fluorophenylnitrene, generated in argon matrices by UV‐irradiation of an azide precursor, was found to spontaneously cyclize to singlet 4‐fluoro‐2,1‐benzisoxazole. Monitoring the transformation by IR spectroscopy, temperature‐independent rate constants (k≈1.4×10−3 s−1; half‐life of ≈8 min) were measured from 10 to 20 K. Computational estimated rate constants are in fair agreement with experimental values, providing evidence for a mechanism involving heavy‐atom QMT through crossing triplet to singlet potential energy surfaces. Moreover, the heavy‐atom QMT takes place with considerable displacement of the oxygen atom, which establishes a new limit for the heavier atom involved in a QMT reaction in cryogenic matrices.

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Section: Introductionmentioning

confidence: 99%

Heavy‐Atom Tunneling Through Crossing Potential Energy Surfaces: Cyclization of a Triplet 2‐Formylarylnitrene to a Singlet 2,1‐Benzisoxazole

et al. 2020

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“…10 K in solid argon), facile tunneling with a half‐live (τ) of only about 1 h entirely dominates the reactivity. Recent examples demonstrate that tunneling is not relevant to cryogenic temperatures , but also for reactions under ambient conditions …”

Section: Introductionmentioning

confidence: 99%

TUNNEX: An easy‐to‐use wentzel‐kramers‐brillouin (WKB) implementation to compute tunneling half‐lives

Quanz

Schreiner

2018

J Comput Chem

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Tunneling in experiments (TUNNEX) is a free open-source program with an easy-to-use graphical user interface to simplify the process of Wentzel-Kramers-Brillouin (WKB) computations. TUNNEX aims at experimental chemists with basic knowledge of computational chemistry, and it offers the computation of tunneling half-lives, visualization of data, and exporting of graphs. It also provides a helper tool for executing the zeropoint vibrational energy correction along the path. The program also enables computing high-level single points along the intrinsic reaction path. TUNNEX is available at https://github. com/prs-group/TUNNEX. As the WKB approximation usually overestimates tunneling half-lives, it can be used to screen tunneling processes before proceeding with elaborate kinetic experiments or higher-level tunneling computations such as instanton theory and small curvature tunneling approaches.

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“…Tunneling-controlled reactivity has been observed in adiabatic reactions at low temperature. [95][96][97] As we have shown in this paper, there are much stronger tunneling effects in nonadiabatic spin-crossing reactions, and thus we expect to find that this interesting phenomenon is widespread in this type of reaction, even at room temperature.…”

Section: Discussionmentioning

confidence: 51%

Spin crossover of thiophosgene via multidimensional heavy-atom quantum tunneling

Heller

Richardson

2021

Preprint

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The spin-crossover reaction of thiophosgene has drawn broad attention from both experimenters and theoreticians as a prime example of radiationless intramolecular decay via intersystem crossing. Despite multiple attempts over 20 years, theoretical predictions have typically been orders of magnitude in error relative to the experimentally measured triplet lifetime. We address the T1 → S0 transition by the first application of semiclassical golden-rule instanton theory in conjunction with on-the-fly electronic-structure calculations based on multireference perturbation theory. Our first-principles approach provides excellent agreement with the experimental rates. This was only possible due to the fact that instanton theory goes beyond previous methods by locating the optimal tunneling pathway in full dimensionality and thus captures "corner cutting" effects. Since the reaction is situated in the Marcus inverted regime, the tunneling mechanism can be interpreted in terms of two classical trajectories, one traveling forwards and one backwards in imaginary time, which are connected by particle--antiparticle creation and annihilation events. The calculated mechanism indicates that the spin crossover is sped up by many orders of magnitude due to multidimensional quantum tunneling of the carbon atom even at room temperature.

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Isotope-Controlled Selectivity by Quantum Tunneling: Hydrogen Migration versus Ring Expansion in Cyclopropylmethylcarbenes

Cited by 27 publications

References 15 publications

Heavy‐Atom Tunneling Through Crossing Potential Energy Surfaces: Cyclization of a Triplet 2‐Formylarylnitrene to a Singlet 2,1‐Benzisoxazole

Heavy‐Atom Tunneling Through Crossing Potential Energy Surfaces: Cyclization of a Triplet 2‐Formylarylnitrene to a Singlet 2,1‐Benzisoxazole

TUNNEX: An easy‐to‐use wentzel‐kramers‐brillouin (WKB) implementation to compute tunneling half‐lives

Spin crossover of thiophosgene via multidimensional heavy-atom quantum tunneling

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