Title: Stabilizing a different cyclooctatetraene stereoisomer

Abstract

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.

Authors:

Li, Longfei ^[1]; Lei, Ming ^[2]; Xie, Yaoming ^[3]; Schaefer, III, Henry F. ^[3]; Chen, Bo ^[4]; Hoffmann, Roald ^[4]

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+ Show Author Affiliations

1. State Key Laboratory of Chemical Resource Engineering, Institute of Materia Medica, College of Science, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China,, Center for Computational Quantum Chemistry, University of Georgia, Athens, GA 30602,
2. State Key Laboratory of Chemical Resource Engineering, Institute of Materia Medica, College of Science, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China,
3. Center for Computational Quantum Chemistry, University of Georgia, Athens, GA 30602,
4. Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853-1301

Publication Date:

Mon Aug 28 00:00:00 EDT 2017

Research Org.:

Univ. of Georgia, Athens, GA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1377094

Alternate Identifier(s):

OSTI ID: 1466011

Grant/Contract Number:  

SC0015512

Resource Type:

Published Article

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Volume: 114 Journal Issue: 37; Journal ID: ISSN 0027-8424

Publisher:

Proceedings of the National Academy of Sciences

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