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Title: Stabilizing a different cyclooctatetraene stereoisomer

An unconventional cis-cis-cis-trans or (Z,Z,Z,E) structure B of cyclooctatetraene (COT) is calculated to lie only 23 kcal/mol above the well-known tub-shaped (Z,Z,Z,Z) isomer A; one example of this type of structure is known. The barrier for B returning to A is small, 3 kcal/mol. However, by suitable choice of substituents, the (Z,Z,Z,E) isomer can be made to lie in energy below the tub-shaped structure. Steric, clamping, and electronic strategies are proposed for achieving this. In the steric strategy, the C 8H 4(CH 3) 2(C( tBu) 3) 2 structure B is predicted to lie 21 kcal/mol below structure A, which is separated from form B only by a small barrier. A simple clamping strategy, effective for COT planarization, does not influence the A/B isomerization much. But, if the clamping group is aromatic (a fused benzene, pyrrole, thiophene, furan), the subtle interplay of potential aromaticity with clamping can be used to confer persistence if not stability on the (Z,Z,Z,E) isomer. Furthermore, an electronic strategy of a different kind, push–pull substitution on the COT ring, was not very effective in stabilizing the B form. However, it led us to vicinal amine–borane-substituted normal COTs that proved to be quite good at activating H 2more » in a frustrated Lewis pair scenario.« less
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [4] ;  [4]
  1. Beijing Univ. of Chemical Technology, Beijing (People's Republic of China); Univ. of Georgia, Athens, GA (United States)
  2. Beijing Univ. of Chemical Technology, Beijing (People's Republic of China)
  3. Univ. of Georgia, Athens, GA (United States)
  4. Cornell Univ., Ithaca, NY (United States)
Publication Date:
Grant/Contract Number:
SC0015512
Type:
Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 114; Journal Issue: 37; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Research Org:
Univ. of Georgia, Athens, GA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; cyclooctatetraene; steric effects; electronic effects; frustrated Lewis pair; molecular orbital theory
OSTI Identifier:
1377094
Alternate Identifier(s):
OSTI ID: 1466011

Li, Longfei, Lei, Ming, Xie, Yaoming, Schaefer, III, Henry F., Chen, Bo, and Hoffmann, Roald. Stabilizing a different cyclooctatetraene stereoisomer. United States: N. p., Web. doi:10.1073/pnas.1709586114.
Li, Longfei, Lei, Ming, Xie, Yaoming, Schaefer, III, Henry F., Chen, Bo, & Hoffmann, Roald. Stabilizing a different cyclooctatetraene stereoisomer. United States. doi:10.1073/pnas.1709586114.
Li, Longfei, Lei, Ming, Xie, Yaoming, Schaefer, III, Henry F., Chen, Bo, and Hoffmann, Roald. 2017. "Stabilizing a different cyclooctatetraene stereoisomer". United States. doi:10.1073/pnas.1709586114.
@article{osti_1377094,
title = {Stabilizing a different cyclooctatetraene stereoisomer},
author = {Li, Longfei and Lei, Ming and Xie, Yaoming and Schaefer, III, Henry F. and Chen, Bo and Hoffmann, Roald},
abstractNote = {An unconventional cis-cis-cis-trans or (Z,Z,Z,E) structure B of cyclooctatetraene (COT) is calculated to lie only 23 kcal/mol above the well-known tub-shaped (Z,Z,Z,Z) isomer A; one example of this type of structure is known. The barrier for B returning to A is small, 3 kcal/mol. However, by suitable choice of substituents, the (Z,Z,Z,E) isomer can be made to lie in energy below the tub-shaped structure. Steric, clamping, and electronic strategies are proposed for achieving this. In the steric strategy, the C8H4(CH3)2(C(tBu)3)2 structure B is predicted to lie 21 kcal/mol below structure A, which is separated from form B only by a small barrier. A simple clamping strategy, effective for COT planarization, does not influence the A/B isomerization much. But, if the clamping group is aromatic (a fused benzene, pyrrole, thiophene, furan), the subtle interplay of potential aromaticity with clamping can be used to confer persistence if not stability on the (Z,Z,Z,E) isomer. Furthermore, an electronic strategy of a different kind, push–pull substitution on the COT ring, was not very effective in stabilizing the B form. However, it led us to vicinal amine–borane-substituted normal COTs that proved to be quite good at activating H2 in a frustrated Lewis pair scenario.},
doi = {10.1073/pnas.1709586114},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 37,
volume = 114,
place = {United States},
year = {2017},
month = {8}
}