Ambiphilic singlet carbenes: Electron donors and acceptors

Kim, Hyunho; Lee, Eunsung

doi:10.1002/bkcs.12620

Cited by 22 publications

(15 citation statements)

References 112 publications

(121 reference statements)

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“…5 NHCs are effective at stabilizing radical centers because of their bulky substituents and low-lying empty orbitals. 6 As a result, several NHC-derived APORs have been developed by the groups of Bertrand, 7 Martin, 8 Roesky, 9 and Han, 10,11 in addition to our own research group 12 (Figure 1a). For example, our group recently reported the synthesis of NHC-derived 1,2-dicarbonyl radical cations ([1] •+ ), 12b which are air-, moisture-, and thermally stable radicals (Figure 1b).…”

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confidence: 99%

Formation of Highly Stable 1,2-Dicarbonyl Organic Radicals from Cyclic (Alkyl)(amino)carbenes

et al. 2023

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Two air-stable organic radicals derived from oxalyl chloride and cAAC were synthesized, resulting in the unexpected formation of a known (amino)(carboxy) radical cation ([2]BF4) and the oxidative formation of a 1,2-dicarbonyl radical cation ([3]BF4) from a neutral 3-oxetanone compound (4). The highly strained and newly discovered 4 was obtained by a single-electron reduction of [3]BF4 with a mild reducing agent. This result differs from the generation of NHC-based 1,2-dicarbonyl radicals, indicating the uniqueness of cAAC.

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Formation of Highly Stable 1,2-Dicarbonyl Organic Radicals from Cyclic (Alkyl)(amino)carbenes

et al. 2023

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“…The triplet SiCBY M1 T adopts a planar four-membered ring (177.6°) and Δ E S‑T of M1 was calculated to be 25.0 kcal mol –1 . The presence of the amino groups pushes up the HOMO energy level by 0.60 eV with respect to the alkyl-substituted counterpart ( M1 : −4.77 eV, M3 : −5.37 eV), and the energy level of M1 is much beyond those of the model carbenes of well-established aminocarbenes calculated at the same level of theory (−5.62 ∼ −4.82 eV). , The longer C1–C3 distance of M1 compared to M3 ( M1 : 2.135 Å, M3 : 1.993 Å) could be explained by the mesomeric effect of the amino groups which decreases the contribution of the 3c-2e (C1–C2–C3)-type interaction. The lower LUMO energy level of M1 compared to M2 ( M1 : −0.50 eV, M2 : −0.27 eV) might be reflecting its longer C1–C3 distance; the out-of-phase interaction between the 2p(C1) and π*(C3–N2) orbitals should be smaller for M1 which results in the lower LUMO energy level.…”

Section: Resultsmentioning

confidence: 94%

Cyclobutenylidene: A Multifaceted Two-Coordinate Carbon Species Obtained via Skeletal Editing of a Cyclopropenylidene

Koike

Iwamoto

2023

J. Am. Chem. Soc.

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C 4 H 4 isomers not only serve as a basis to understand the chemical properties of hydrocarbons but are possible intermediates in combustion and organic reactions in outer space. Cyclobutenylidene (CBY), an elusive C 4 H 4 isomer, is often proposed as a key intermediate in transition-metal-catalyzed metathesis and cycloaddition reactions between carbon−carbon multiple bonds. The geometrical structure of cyclobutenylidene predicted by calculations had been debated as whether it should be regarded as a carbocyclic carbene or a strained bridgehead alkene. Here, we report the synthesis of a crystalline cyclobutenylidene derivative, namely, a 3-silacyclobut-2-en-4-ylidene (SiCBY) via "carbene-to-carbene ring-expansion" reaction of an isolable diaminocyclopropenylidene induced by a silicon analogue of a carbene (silylene). The SiCBY exhibits multifaceted electronic properties which are corroborated by its extremely strong electron-donating properties and ambiphilic reactivity toward small gaseous molecules and C−H bonds. This result introduces an exciting strategy as well as a molecular motif to access low-valent carbon species with unusual electronic properties.

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“…[6] NHCs are effective at stabilizing radical centers because of their bulky substituents and low-lying empty orbitals. [7] As a result, several NHC-derived APORs have been developed by the groups of Bertrand, [8] Martin, [9] Roesky, [10] and Han, [11] in addition to our own research group [12] (Figure 1a). For example, our group recently reported the synthesis of NHC-derived 1,2-dicarbonyl radical cations ([1] + ), [12b] which are air-, moisture-, and thermally stable radicals (Figure 1b).…”

Section: Main Textmentioning

confidence: 99%

Formation of Highly Stable 1,2-Dicarbonyl Organic Radicals from Cyclic (Alkyl)(amino)carbenes

Choe

Song

Choi

et al. 2023

Preprint

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The synthesis of air-persistent organic radicals (APORs) is challenging because of the presence of highly reactive species in air. It was found that N-heterocyclic carbenes (NHCs) are effective in stabilizing radical centers because of their bulky substituents and low-lying empty orbitals, thereby leading to the development of several APORs. Herein, we report the synthesis of two air-stable organic radicals derived from oxalyl chloride and cyclic (alkyl)(amino)carbene (cAAC), which included the unexpected formation of a known (amino)(carboxy) radical cation ([2]BF4) and a 1,2-dicarbonyl radical cation ([3]BF4). Most importantly, the reduced 3-oxetanone compound (4) was discovered as a new product originating from [3]BF4, which differs from the generation of NHC-based 1,2-dicarbonyl radicals. The highly strained 3-oxetanone 4 was obtained by a single-electron reduction of [3]BF4 with a mild reducing agent, chloride salt, and vice versa with a AgBF4 oxidant. Both [2]BF4 and [3]BF4 retained their intrinsic blue color and exhibited high air stability. Furthermore, [3]BF4 produced a temperature-dependent electron paramagnetic resonance spectrum.

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Ambiphilic singlet carbenes: Electron donors and acceptors

Cited by 22 publications

References 112 publications

Formation of Highly Stable 1,2-Dicarbonyl Organic Radicals from Cyclic (Alkyl)(amino)carbenes

Formation of Highly Stable 1,2-Dicarbonyl Organic Radicals from Cyclic (Alkyl)(amino)carbenes

Cyclobutenylidene: A Multifaceted Two-Coordinate Carbon Species Obtained via Skeletal Editing of a Cyclopropenylidene

Formation of Highly Stable 1,2-Dicarbonyl Organic Radicals from Cyclic (Alkyl)(amino)carbenes

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