Free Radical Reactivity of a Phosphaalkene Explored Through Studies of Radical Isotopologues

Chandrasena, Lalangi; Samedov, Kerim; McKenzie, Iain; Mozafari, Mina; West, Robert; Gates, Derek P.; Percival, Paul W.

doi:10.1002/ange.201810967

Cited by 8 publications

(10 citation statements)

References 69 publications

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“…This is rare, but in recent years we have reported several instances of related behaviour, where the amplitudes of precession frequencies vary sinusoidally with the delay between the muon stop and the time window used to Fourier transform the data. 14,[36][37][38] Careful examination of the allene data set revealed some effect for radicals 2b and 2d but not the others. The phenomenon of oscillating signal amplitudes is under examination in other systems where the effect is more marked.…”

Section: Further Discussionmentioning

confidence: 99%

Free Radicals Formed by H Atom Addition to Allenes as Determined by Muon Spin Spectroscopy

Scollon

Percival

2020

J. Phys. Chem. A

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Allyl and vinyl radicals are important intermediates in diverse areas of chemistry, ranging from combustion to synthesis. However, questions remain about the competitive formation of these radicals from allenes. Here we present a study of prototypical allyl and vinyl radicals formed by H atom addition to allenes. They were studied by forming the analogous muonium adducts, since muonium (Mu) behaves as a light isotope of hydrogen, and muoniated species can be characterized by muon spin spectroscopy. Two techniques were employed: Transverse-Field Muon Spin Resonance (TF-μSR), and Muon Level Crossing Resonance (µLCR), which allow for the measurement of muon hyperfine constants (hfcs) and other nuclear hfcs, respectively, and thus aid identification of the formed radicals. TF-μSR has already been used to determine that two radicals are formed by Mu addition to 1,1-dimethylallene, but µLCR techniques were undeveloped at the time of that study, so assignments were based on ESR data of similar allyl and vinyl radicals. We report here the muon spin spectroscopy of multiple radicals detected from positive muon irradiation of 1,1-dimethylallene and 1-methoxyallene in solution. The radicals were identified by comparison of muon and proton hfcs with ESR data and the results of DFT calculations. The conclusion is that muonium (and by extension, the H atom) can add to all three carbons of the allene system, albeit with preference for the central carbon.

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Section: Further Discussionmentioning

confidence: 99%

Free Radicals Formed by H Atom Addition to Allenes as Determined by Muon Spin Spectroscopy

Scollon

Percival

2020

J. Phys. Chem. A

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“…In recent years we have applied muon spin spectroscopy to study the radical chemistry of low‐valent molecules containing silicon, germanium, and phosphorus . By studying monomer radicals we are able to gain more insight into the mechanism of polymerization, specifically the initial step of selective addition of radicals to different sites in the monomer. In addition, the structure of the parent compound can influence the possibility of migration of the radical centre, resulting in a different structure of the repeating unit of the polymer .…”

Section: Methodsmentioning

confidence: 99%

Free Radical Chemistry of Phosphasilenes

et al. 2020

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Understanding the characteristics of radicals formed from silicon‐containing heavy analogues of alkenes is of great importance for their application in radical polymerization. Steric and electronic substituent effects in compounds such as phosphasilenes not only stabilize the Si=P double bond, but also influence the structure and species of the formed radicals. Herein we report our first investigations of radicals derived from phosphasilenes with Mes, Tip, Dur, and NMe2 substituents on the P atom, using muon spin spectroscopy and DFT calculations. Adding muonium (a light isotope of hydrogen) to phosphasilenes reveals that: a) the electron‐donor NMe2 and the bulkiest Tip‐substituted phosphasilenes form several muoniated radicals with different rotamer conformations; b) bulky Dur‐substituted phosphasilene forms two radicals (Si‐ and P‐centred); and c) Mes‐substituted phosphasilene mainly forms one species of radical, at the P centre. These significant differences result from intramolecular substituent effects.

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“…In 2019, Gates and Percival and coworkers reported μSR studies for elucidating free radical reactivity of phosphaalkenes by using 3. [13] not been fully understood, it seems to indicate delayed formation of a radical. [4b] μLCR was employed for confirming the muonium radicals generated from 3 and 4, because the Δ 0 (ΔM = 0) transitions could determine hfcs of the I = 1/2 nuclei ( 31 P and 1 H).…”

Section: Muonium Addition To An Acyclic Phosphaalkenementioning

confidence: 99%

“…This TF-μSR spectrum is compatible with the regioselective addition of muonium to 6 affording single observable radical species, which is in sharp contrast to the muoniation of anthracene affording three (or four) paramagnetic species. [19] Taking the potent high reactivity of P=C into account (see μSR of 3 in Section 3.1), [13] muonium would predominantly add to the phosphorus atom, and the benzene rings are reluctant to accept muonium. To confirm the regioselective muoniation, we conducted μLCR experiments with an isotropic solution sample of 6.…”

Section: μSr Studies Of a Peri-trifluoromethyl-substituted 9-phosphaa...mentioning

confidence: 99%

Muon Spin Rotation/Resonance (μSR) for Studying Radical Reactivity of Unsaturated Organophosphorus Compounds

Ito

2022

Chemistry A European J

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The positive muon (μ+) can be regarded as a light isotope of proton and has been an important tool to study radical reactions of organic compounds. Recently, muons have been applied to produce short‐lived paramagnetic species from the heavier unsaturated organic molecules including the p‐block elements. This article overviews recent muon spin rotation/resonance (μSR) studies on the phosphorus analogs of alkenes, anthracenes, and cyclobutane‐1,3‐diyls together with the fundamentals of μSR. The acyclic phosphaalkene of P=C and phosphasilenes of P=Si can accept muonium (Mu=[μ+e−]) at the heavier double bonds, and the corresponding radicals have been characterized. The phosphorus atom in 9‐phosphaanthracene, whose P=C double bond is stabilized by the peri‐substituted CF3 groups, predominantly captures muonium to provide the corresponding paramagnetic fused heterocyclic system. The peri‐trifluoromethyl groups are functional to promote the unprecedented light isotope effect of muon providing the planar three‐cyclic molecular structure to consume the increased zero‐point energy. The formally open‐shell singlet 1,3‐diphosphacyclobutane‐2,4‐diyl unit can accept muonium at the (ylidic) phosphorus or the skeletal radicalic carbon, and the corresponding paramagnetic phosphorus heterocycles can be characterized by μSR. The findings on these muoniation processes to the unsaturated phosphorus‐containing compounds will contribute not only to development of novel paramagnetic functional species but also to progress on muon science.

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Free Radical Reactivity of a Phosphaalkene Explored Through Studies of Radical Isotopologues

Cited by 8 publications

References 69 publications

Free Radicals Formed by H Atom Addition to Allenes as Determined by Muon Spin Spectroscopy

Free Radicals Formed by H Atom Addition to Allenes as Determined by Muon Spin Spectroscopy

Free Radical Chemistry of Phosphasilenes

Muon Spin Rotation/Resonance (μSR) for Studying Radical Reactivity of Unsaturated Organophosphorus Compounds

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