The Chemistry, Kinetics, and Mechanisms of Triplet Carbene Processes in Low-Temperature Glasses and Solids

Platz, Matthew S.

doi:10.1007/978-1-4899-3707-0_6

Cited by 24 publications

(24 citation statements)

References 88 publications

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“…While the reduction of the EPR intensity at 100 K was nonexponential, the initial 20% of the decay could be simulated with a rate constant of 1.3(1) × 10 –3 s –1 ( SI ), following the approach described previously. 49 These data show that triplet vinylidene 2 in toluene is more stable than diphenylcarbene, for which an initial rate constant of 6.7 × 10 –3 s –1 at 99 K has been reported. 49 …”

Section: Resultsmentioning

confidence: 65%

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Characterization of a Triplet Vinylidene

et al. 2021

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Singlet vinylidenes (R 2 C=C:) are proposed as intermediates in a series of organic reactions, and very few have been studied by matrix isolation or gas-phase spectroscopy. Triplet vinylidenes, however, featuring two unpaired electrons at a monosubstituted carbon atom are thus far only predicted as electronically excited-state species and represent an unexplored class of carbon-centered diradicals. We report the photochemical generation and low-temperature EPR/ENDOR characterization of the first ground-state high-spin (triplet) vinylidene. The zero-field splitting parameters ( D = 0.377 cm –1 and | E| / D = 0.028) were determined, and the 13 C hyperfine coupling tensor was obtained by 13 C-ENDOR measurements. Most strikingly, the isotropic 13 C hyperfine coupling constant (50 MHz) is far smaller than the characteristic values of triplet carbenes, demonstrating a unique electronic structure which is supported by quantum chemical calculations.

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Section: Resultsmentioning

confidence: 65%

“… 49 These data show that triplet vinylidene 2 in toluene is more stable than diphenylcarbene, for which an initial rate constant of 6.7 × 10 –3 s –1 at 99 K has been reported. 49 …”

Section: Resultsmentioning

confidence: 65%

Characterization of a Triplet Vinylidene

et al. 2021

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“…Our interpretation of the product analysis and spectroscopic data as a function of reaction media is based on the reaction pathways illustrated in Scheme 4. While it is well established that carbenes can be generated efficiently by photochemical excitation of diazo compounds both at ambient temperature and at 77 K, 20 the formation of oxonium ylides by reaction with ethers has been inferred mainly from product analysis studies. 21 The spectroscopic detection of oxonium ylides in solution by laser flash photolysis has been limited to a few carbenes with a singlet ground state.…”

Section: Reactions Of Carbenes and Oxonium Ylidesmentioning

confidence: 99%

Photochemical generation, intramolecular reactions, and spectroscopic detection of oxonium ylide and carbene intermediates in a crystalline ortho-(1,3-dioxolan-2-yl)-diaryldiazomethane

Dang

2009

Org. Biomol. Chem.

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Photochemical excitation of a diaryldiazomethane with an ortho-acetal both in solution and in crystals led to products that originate from the expected diarylcarbene and form an intramolecular oxonium ylide. While crystals strongly favored the formation of a benzocyclobutane by intramolecular hydrogen abstraction in the triplet carbene, reactions in benzene led exclusively to products that derive from the oxonium ylide. Studies in methyl cyclohexane glasses and in mixed crystals at 77 K led to the spectroscopic detection of triplet carbene (3)C, which partially transformed into a new species that we assign as the sought-after oxonium ylide Y. The formation of a formally ionic intermediate suggests that the scope of reactions by reactive intermediates in crystalline solids may be broader than it is generally assumed.

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“…The photochemistry of 1,2-diphenyldiazoalkanes has been studied in fluid solutions and glassy matrices. , Even subtle changes in experimental conditions affect the product yields in a relatively complex manner, but selectivity remains low under all reaction conditions. − Accordingly, irradiation of ca. 10 -3 M 1 in deoxygenated hexane or acetonitrile with λ > 380 nm leads to formation of both Z and E isomers (indicated by Z and E after the compound number) of olefins 3 and 4 in yields that depend on the solvent used (Scheme )…”

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confidence: 99%

“…Experimental and theoretical results suggest that 1,2-H shifts in singlet state carbenes possess highly ordered transition states with conformations that require a parallel alignment of the migrating σ-bond with the carbene p-orbital . It is generally accepted that carbenes with ground triplet states react from thermally populated singlets. , As indicated in Scheme , it is expected that different products must arise from different conformers. Thus, to the extent that all conformers are present in solution, all the products with energetically accessible transition states should have an opportunity to form.…”

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confidence: 99%