Zweistufige Selbstassoziation von [4]‐ und [5]Catenanen

Amabilino, David B.; Ashton, Peter R.; Reder, Anatoli S.; Spencer, Neil; Stoddart, J. Fraser

doi:10.1002/ange.19941060412

Cited by 32 publications

(2 citation statements)

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“…6 Exit and entry of the guest molecule proceed only at higher temperature with a substantial activation barrier resulting from opening and closing of a gate by conformational distortion of the host geometry, which is required for guest movement in‐ and outside the host cavity 7. 8 Other examples of kinetically highly stable supramolecules are the catenanes9 and rotaxanes,10–12 in which two or more rings or a molecular wheel and a molecular axis are mechanically interlocked. In these systems the intramolecular dynamics (in catenanes, movement of the rings relative to each other, and in the rotaxanes, “shuttling” of the wheel along the molecular axis)13, 14 are of considerable interest, for example, in connection with the construction of molecular devices 15.…”

Section: Introductionmentioning

confidence: 99%

Dynamics in Host–Guest Complexes of Molecular Tweezers and Clips

Lobert

Bandmann

Burkert

et al. 2006

Chemistry A European J

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The dynamics in the host-guest complexes of the molecular tweezers 1 a,b and clips 2 a,b with 1,2,4,5-tetracyanobenzene (TCNB, 3) and tropylium tetrafluoroborate (4) as guest molecules were analyzed by temperature-dependent 1H NMR spectroscopy. The TCNB complexes of tweezers 1 a,b were found to be particularly stable (dissociation barrier: DeltaG(++)=16.8 and 15.7 kcal mol(-1), respectively), more stable than the TCNB complexes of clips 2 a,b and the tropylium complex of tweezer 1 b (dissociation barrier: DeltaG(++)=12.4, 11.2, and 12.3 kcal mol(-1), respectively). A detailed analysis of the kinetic and thermodynamic data (especially the negative entropies of activation found for complex dissociation) suggests that in the transition state of dissociation the guest molecule is still clipped between the aromatic tips of the host molecule. The 1H NMR analysis of the TCNB complexes 3@1 b and 3@2 a at low temperatures (T<-80 degrees C) showed that 3 undergoes fast rotation inside the cavity of tweezer 1 b or clip 2 a (rotational barrier: DeltaG( not equal)=11.7 and 8.3 kcal mol(-1), respectively). This rotation of a guest molecule inside the host cavity can be considered to be the dynamic equilibration of noncovalent conformers. In the case of clip complex 3@2 a the association and rotational barriers are smaller by DeltaDeltaG(++)=3-4 kcal mol(-1) than those in tweezer complexes 3@1 a,b. This can be explained by the more open topology of the trimethylene-bridged clips compared to the tetramethylene-bridged tweezers. Finally, the bromo substituents in the newly prepared clip 2 b have a substantial effect on the kinetics and thermodynamics of complex formation. Clip 2 b forms weaker complexes with (TCNB, 3) and tetracyanoquinodimethane (TCNQ, 12) and a more stable complex with 2,4,7-trinitrofluoren-9-ylidene (TNF, 13) than the parent clip 2 a. These results can be explained by a less negative electrostatic potential surface (EPS) inside the cavity and a larger van der Waals contact surface of 2 b compared to 2 a. In the case of the highly electron-deficient guest molecules TCNB and TCNQ the attractive electrostatic interaction is predominant and hence responsible for the thermodynamic complex stability, whereas in the case of TNF with its extended pi system, dispersion forces are more important for host-guest binding.

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Section: Introductionmentioning

confidence: 99%

Dynamics in Host–Guest Complexes of Molecular Tweezers and Clips

Lobert

Bandmann

Burkert

et al. 2006

Chemistry A European J

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“…The molecular recognition properties of 'Blue Box' have recently drawn great attention due to its important applications in the design and synthesis of various electrochemically active molecular systems [3][4][5][6][7][8][9][10][11][12][13][14][15]. Many molecular machines based on 'Blue Box' take into consideration two key properties of this compound: i) the ability to interact with guests by π−π stacking and chargetransfer interactions [1,[16][17] and ii) the presence of a rigid cavity which helps to trap the guests, giving inclusion complexes [18][19][20][21][22].…”

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confidence: 99%

Unexpected Keto-enol Tautomerism in the Cyclopyridinophane Class Direct and indirect proofs

Dron¹,

Miron²,

Surpateanu³

2008

Rev. Chim.

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The paper presents the synthesis of cyclo (bis-paraquat p-phenylene p-phenylene-carbonyl) tetrakis (hexafluorophosphate), named �CETOBOX�, and the closely related structural determinations. This compound exists in three tautomeric forms. These forms were evidentiated by NMR-data (1H-NMR, TOCSY, COSY, NOESY), UV-Vis spectra coupled with pH measurements and by synthesis. As the �CETOBOX� gives �in situ� only the corresponding monoylide, the synthesis of a new fluorescent indolizine cyclophane has been performed by a 3+2 cycloaddition. All structures of the new compounds presented herein have been established by NMR spectroscopy. Also, theoretical methods (MM3, AM1, AM1-COSMO and B88LYPDFT) have been used to determine the most stable conformer structures.

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