Strained Olefins: Structure and Reactivity of Nonplanar Carbon‐Carbon Double Bonds

Luef, Wolfgang; Keese, Reinhart

doi:10.1002/9780470147290.ch4

Cited by 81 publications

(12 citation statements)

References 371 publications

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“…We discuss here some noteworthy structural features. 19 The length of the central double bond of all eight compounds is almost invariant, each alkene deviating from the average of 1.351 Å by at most 0.002 Å. In all eight structures, both carbon atoms of the central alkene are very close to ideal planarity, as indicated by the sum of their bond angles, which in all cases falls between 359.9° and 360.1°.…”

Section: Resultsmentioning

confidence: 85%

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All-Photochemical Rotation of Molecular Motors with a Phosphorus Stereoelement

et al. 2020

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Unidirectional molecular rotation based on alternating photochemical and thermal isomerizations of overcrowded alkenes is well established, but rotary cycles based purely on photochemical isomerizations are rare. Herein we report three new second-generation molecular motors featuring a phosphorus center in the lower half, which engenders a unique element of axial chirality. These motors exhibit unusual behavior, in that all four diastereomeric states can interconvert solely photochemically. Kinetic analysis and modeling reveal that the behavior of the new motors is consistent with all-photochemical unidirectional rotation. Furthermore, X-ray crystal structures of all four diastereomeric states of two of these new motors were obtained, which constitute the first achievements of crystallographic characterization of the full 360° rotational cycle of overcrowded-alkene-based molecular motors. Finally, the axial phosphorus stereoelement in the phosphine motor can be thermally inverted, and this epimerization enables a “shortcut” of the traditional rotational cycle of these compounds.

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Section: Resultsmentioning

confidence: 85%

“…ORTEP representations of compounds 2a – d and 3a – d are shown in Figure , and selected metrics are given in Table . We discuss here some noteworthy structural features . The length of the central double bond of all eight compounds is almost invariant, each alkene deviating from the average of 1.351 Å by at most 0.002 Å.…”

Section: Resultsmentioning

confidence: 90%

All-Photochemical Rotation of Molecular Motors with a Phosphorus Stereoelement

et al. 2020

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“…We have previously described the syntheses and stereochemistry of homomerous selenium-and telluriumbridged BAEs (Scheme 2) diselenoxanthylene (7) and ditelluroxanthylene (8) [26]. Dithioxanthylene (6) has also been synthesized [27].…”

Section: Introductionmentioning

confidence: 98%

“…The BAEs are nonplanar and overcrowded in the fjord regions. There are two principal modes of out-of-plane deformations in 1: twisting around the central double bond (C 9 =C 9 0 ) and outof-plane bending, realized by folding of the tricyclic moieties [8]. In addition, C 9 and C 9 0 may be pyramidalized [1,[3][4][5].…”

Section: Introductionmentioning

confidence: 99%

Selenium- and tellurium-bridged heteromerous overcrowded bistricyclic aromatic enes with central six-member and seven-member rings

et al. 2015

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A series of selenium-bridged and telluriumbridged heteromerous bistricyclic aromatic enes (BAEs) 15-25 with six-member and seven-member central rings have been synthesized by Barton-Kellogg olefination, twofold extrusion coupling method between tricyclic aromatic thiones and tricyclic aromatic diazo derivatives. The crystal structures of thioxanthenylidene-anthracenone (15), selenoxanthenylidene-anthracenone (20), and telluroxanthenylidene-anthracenone (21) were determined. The ordered crystal structure of 21 showed a very high degree of folding of the telluroxanthenylidene moiety (58.5°) and very short intramolecular TeÁÁÁC 9 0 contact distance, indicating [20 % penetration which may reflect secondary nonbonding interactions and lack of aromatic telluroxanthenylium-anthracenolate contribution. The BAEs were subjected to a 1 H-, 13 C-, 77 Se-, and 125 Te-NMR spectroscopic study. The 1 H-NMR spectra indicated anti-folded conformations in solution. The measured pronounced downfield 77 Se-and 125 Te-NMR shifts in 20 and 21, relative to the corresponding spectra of homomerous BAEs diselenoxanthylene (7) and ditelluroxanthylene (8), may be due to the proximity of the Se and Te bridges to the carbons of the central enes in the anti-folded conformations. This deshielding effect was larger in 21 than in 20, d( 125 Te)/d( 77 Se) = 1.53, a ratio higher than in any other member of the series.

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“…In spite of the enormous strain and high olefinic pyramidalization, [31] perchlorinated dienes 20, in line with the allylically brominated dodecahedrenes, [1] showed no tendency for dimerization, sublimed neatly at 320 8C/10 À4 Torr, and remained inert in an oxygen atmosphere for weeks. Furthermore, they did not add electrophiles (e.g.…”

Section: Introductionmentioning

confidence: 99%

Towards Perfunctionalized Dodecahedranes—En Route to C₂₀ Fullerene

Wahl

Weiler

Landenberger

et al. 2006

Chemistry A European J

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"One-pot" substitution of the twenty hydrogen atoms in pentagonal dodecahedrane (C(20)H(20)) by OH, F, Cl, and Br atoms is explored. Electrophilic insertion of oxygen atoms with DMDO and TFMDO as oxidizing reagents ended, far off the desired C(20)(OH)(20), in complex polyol mixtures (up to C(20)H(10)(OH)(10) decols, a trace of C(20)H(OH)(19)?). Perfluorination was successful in a NaF matrix but (nearly pure) C(20)F(20) could be secured only in very low yield. "Brute-force" photochlorination (heat, light, pressure, time) provided a mixture of hydrogen-free, barely soluble C(20)Cl(16) dienes in high yield and C(20)Cl(20) as a trace component. Upon electron-impact ionization of the C(20)Cl(16) material sequential loss of the chlorine atoms was the major fragmentation pathway furnishing, however, only minor amounts of chlorine-free C(20) (+) ions. "Brute-force" photobrominations delivered an extremely complex mixture of polybromides with C(20)HBr(13) trienes as the highest masses. The MS spectra exhibited exclusive loss of the Br substituents ending in rather intense singly, doubly, and triply charged C(20)H(4-0) (+(2+)(3+)) ions. The insoluble approximately C(20)HBr(13) fraction (C(20)Br(14) trienes as highest masses) obtained along a modified bromination protocol, ultimately allowed the neat mass selection of C(20) (-) ions. The C(20)Cl(16) dienes and C(20)H(0-3)Br(14-12) tri-/tetraenes, in spite of their very high olefinic pyramidalization, proved resistant to oxygen and dimerization (polymerization) but added CH(2)N(2) smoothly. Dehalogenation of the respective cycloaddition products through electron-impact ionization resulted in C(22-24)H(4-8) (+(2+)) ions possibly constituting bis-/tris-/tetrakis-methano-C(20) fullerenes or partly hydrogenated C(22), C(23), and C(24) cages.

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Strained Olefins: Structure and Reactivity of Nonplanar Carbon‐Carbon Double Bonds

Cited by 81 publications

References 371 publications

All-Photochemical Rotation of Molecular Motors with a Phosphorus Stereoelement

All-Photochemical Rotation of Molecular Motors with a Phosphorus Stereoelement

Selenium- and tellurium-bridged heteromerous overcrowded bistricyclic aromatic enes with central six-member and seven-member rings

Towards Perfunctionalized Dodecahedranes—En Route to C₂₀ Fullerene

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Strained Olefins: Structure and Reactivity of Nonplanar Carbon‐Carbon Double Bonds

Cited by 81 publications

References 371 publications

All-Photochemical Rotation of Molecular Motors with a Phosphorus Stereoelement

All-Photochemical Rotation of Molecular Motors with a Phosphorus Stereoelement

Selenium- and tellurium-bridged heteromerous overcrowded bistricyclic aromatic enes with central six-member and seven-member rings

Towards Perfunctionalized Dodecahedranes—En Route to C20 Fullerene

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Towards Perfunctionalized Dodecahedranes—En Route to C₂₀ Fullerene