Kinetic Stabilization and Reactivity of π Single‐Bonded Species: Effect of the Alkoxy Group on the Lifetime of Singlet 2,2‐Dialkoxy‐1,3‐diphenyloctahydropentalene‐1,3‐diyls

Nakagaki, Tomoyuki; Sakai, Tomoko; Mizuta, Tsutomu; Fujiwara, Yoshihisa; Abe, Manabu

doi:10.1002/chem.201300038

Cited by 31 publications

(48 citation statements)

References 91 publications

(49 reference statements)

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“…The propoxy-substituted 1,3-diyl CP3d (OR = OR¤ = O n C 3 H 7 ,¸2 93 = ca. 2100 ns, Entry 4) 26 was longer than CP3a (OR = OR¤ = OC 2 H 5 ,¸2 93 = ca. 900 ns, Entry 1), 18 and CP3b (OR = OR¤ = OCH 3 ,¸2 93 = ca.…”

Section: Reactivity Of π-Single Bonded Speciesmentioning

confidence: 95%

Is π-Single Bonding (C–π–C) Possible? A Challenge in Organic Chemistry

Abe

Akisaka

2017

Chem. Lett.

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Rikuo Akisaka received his Bachelor's degree in 2016 from University of Tsukuba. He is currently a master's program student at the department of chemistry, graduate school of science, Hiroshima University, under the supervision of professor Manabu Abe. His current research focuses on steric effect on the reactivity of singlet 2,2-dialkoxy-1,3-diyls. AbstractChemical bonding systems determine the nature of molecules. In organic chemistry, there are two bonding types for carbon carbon connections: σ-bonding and π-bonding. In this Highlight Review, several aspects of studies in the last two decades addressing a naive question "Is π-single bonding (CπC) possible?" were reviewed: (1) features of π-single bonded species; (2) molecular design for π-single bonding; (3) generation and detection of singlet diradicaloids with a π-single bonding character; (4) future prospects of π-single bonded species.

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Section: Reactivity Of π-Single Bonded Speciesmentioning

confidence: 95%

Is π-Single Bonding (C–π–C) Possible? A Challenge in Organic Chemistry

Abe

Akisaka

2017

Chem. Lett.

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“…The singlet diradicals are, in general, quite short-lived species due to the very fast radical–radical coupling reaction [3]. However, in the past decade, the singlet diradicals have been observed or even isolated in cyclic systems such as cyclobutane-1,3-diyls [4–20] and cyclopentane-1,3-diyls [17,21–26]. Detailed experimental study of singlet diradical chemistry is thus now possible using the long-lived localized singlet diradicals.…”

Section: Introductionmentioning

confidence: 99%

“…The 2,2-electron-withdrawing-group-substituted singlet 1,3-diradicals are categorized as Type-1 diradicals [1,27], which possess a π-single-bonding character (–π–, closed-shell character) between the two radical sites. The role of the alkoxy group (OR) on the lifetime ( k = 1/τ) was investigated by combined studies of experiments and quantum chemical calculations [26,28]. The steric repulsion between the alkoxy group and the phenyl ring, which is indicated in the transition-state structure for the ring-closing reaction (Scheme 1), was found to play an important role in determining the energy barrier of the ring-closing process, τ 293 = 292 ns ( DRa : OR = OCH 3 , λ max = 574 nm) and 2146 ns ( DRb : OR = OC 10 H 21 , λ max = 572 nm) [26].…”

Section: Introductionmentioning

confidence: 99%

“…The role of the alkoxy group (OR) on the lifetime ( k = 1/τ) was investigated by combined studies of experiments and quantum chemical calculations [26,28]. The steric repulsion between the alkoxy group and the phenyl ring, which is indicated in the transition-state structure for the ring-closing reaction (Scheme 1), was found to play an important role in determining the energy barrier of the ring-closing process, τ 293 = 292 ns ( DRa : OR = OCH 3 , λ max = 574 nm) and 2146 ns ( DRb : OR = OC 10 H 21 , λ max = 572 nm) [26]. The study prompted us to further investigate the kinetic stabilization of the singlet diradical species.…”

Section: Introductionmentioning

confidence: 99%

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Substituent effect on the energy barrier for σ-bond formation from π-single-bonded species, singlet 2,2-dialkoxycyclopentane-1,3-diyls

Fujiwara²,

Abe

2013

Beilstein J. Org. Chem.

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Summary Background: Localized singlet diradicals are in general quite short-lived intermediates in processes involving homolytic bond-cleavage and formation reactions. In the past decade, long-lived singlet diradicals have been reported in cyclic systems such as cyclobutane-1,3-diyls and cyclopentane-1,3-diyls. Experimental investigation of the chemistry of singlet diradicals has become possible. The present study explores the substituents and the effect of their substitution pattern at the C(1)–C(3) positions on the lifetime of singlet octahydropentalene-1,3-diyls to understand the role of the substituents on the reactivity of the localized singlet diradicals. Results: A series of singlet 2,2-dialkoxy-1,3-diaryloctahydropentalene-1,3-diyls DR were generated in the photochemical denitrogenation of the corresponding azoalkanes AZ. The ring-closed products CP, i.e., 3,3-dialkoxy-2,4-diphenyltricyclo[3.3.0.02,4]octanes, were quantitatively obtained in the denitrogenation reaction. The first-order decay process (k = 1/τ) was observed for the fate of the singlet diradicals DR (λmax ≈ 580–590 nm). The activation parameters, ΔH ‡ and ΔS ‡, for the ring-closing reaction (σ-bond formation process) were determined by the temperature-dependent change of the lifetime. The energy barrier was found to be largely dependent upon the substituents Ar and Ar’. The singlet diradical DRf (Ar = 3,5-dimethoxyphenyl, OCH2Ar’ = OCH2(3,5-dimethoxyphenyl)) was the longest-lived, τ293 = 5394 ± 59 ns, among the diradicals studied here. The lifetime of the parent diradical DR (Ar = Ph, OCH2Ar’ = OCH3) was 299 ± 2 ns at 293 K. Conclusion: The lifetimes of the singlet 1,3-diyls are found to be largely dependent on the substituent pattern of Ar and Ar’ at the C(1)–C(3) positions. Both the enthalpy and entropy effect were found to play crucial roles in increasing the lifetime.

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“…The activation of CO with diphosphadiazanediyl already occurs at ambient temperatures (1 bar, 25 8C). However, trapping products, [9][10][11][12] ringclosed species (housanes), [4,5,10,[13][14][15][16] or cyclopentenes after group migration [11,17] were obtained. [1] Owing to the existence of two unpaired electrons in these molecules, their isolation is generally difficult and only possible if steric congestion is utilized to diminish their reactivity.…”

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confidence: 99%

Stable Heterocyclopentane‐1,3‐diyls

2015

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Diphosphadiazanediyl, [(μ-NR)P]2 (R=Ter=2,6-dimesitylphenyl), is known to readily activate small molecules with multiple bonds. CO is an especially intriguing species for activation, because either 1,1- or 1,2-bridging mode would lead to a [1.1.1]bicycle or a carbene, respectively. The activation of CO with diphosphadiazanediyl already occurs at ambient temperatures (1 bar, 25 °C). However, CO is involved in an unprecedented ring expansion reaction under preservation of the biradical character, which leads to the formation of the first stable cyclopentane-1,3-diyl analogue displaying photochromic molecular switch characteristics.

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Kinetic Stabilization and Reactivity of π Single‐Bonded Species: Effect of the Alkoxy Group on the Lifetime of Singlet 2,2‐Dialkoxy‐1,3‐diphenyloctahydropentalene‐1,3‐diyls

Cited by 31 publications

References 91 publications

Is π-Single Bonding (C–π–C) Possible? A Challenge in Organic Chemistry

Is π-Single Bonding (C–π–C) Possible? A Challenge in Organic Chemistry

Substituent effect on the energy barrier for σ-bond formation from π-single-bonded species, singlet 2,2-dialkoxycyclopentane-1,3-diyls

Stable Heterocyclopentane‐1,3‐diyls

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