TY - JOUR
T1 - Stabilizing a different cyclooctatetraene stereoisomer
AU - Li, Longfei
AU - Lei, Ming
AU - Xie, Yaoming
AU - Schaefer, Henry F.
AU - Chen, Bo
AU - Hoffmann, Roald
N1 - Funding Information:
the National Natural Science Foundation of China-Guangdong Joint Fund (the second phase) for providing some of the computational resources.
Funding Information:
ACKNOWLEDGMENTS. At the University of Georgia, this research was supported by the Department of Energy, Basic Energy Sciences, Computational and Theoretical Chemistry Program, Grant DE-SC0015512. At Cornell University, this work was supported by the National Science Foundation through Grant CHE-1305872. This work was also supported by the National Natural Science Foundation of China (Grants 21672018, 2161101308, and 21373023), Beijing Municipal Natural Science Foundation (Grant 2162029), the Fundamental Research Funds for the Central Universities of China
Funding Information:
(Grant PYCC1708), and China Scholarship Council (201606880007). We thank the Special Program for Applied Research on Supercomputation of
Publisher Copyright:
© 2017, National Academy of Sciences. All rights reserved.
PY - 2017/9/12
Y1 - 2017/9/12
N2 - 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. 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.
AB - 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. 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.
UR - http://www.scopus.com/inward/record.url?scp=85029438291&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85029438291&partnerID=8YFLogxK
U2 - 10.1073/pnas.1709586114
DO - 10.1073/pnas.1709586114
M3 - Article
C2 - 28847954
AN - SCOPUS:85029438291
SN - 0027-8424
VL - 114
SP - 9803
EP - 9808
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 37
ER -