Quantum-Mechanical Study of the Reaction Mechanism for 2π–2π Cycloaddition of Fluorinated Methylene Groups

Perfluorocyclobutyl polymers are thermally and chemically stable, may be produced without a catalyst via thermal 2π–2π cycloaddition, and can form block structures, making them suitable for commercialization of specialty polymers. Thermal 2π–2π cycloaddition is a rare reaction that begins in the sin...

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Bibliographic Details
Published in:Journal of organic chemistry 2017-07, Vol.82 (13), p.6578-6585
Main Authors: Motz, Andrew R, Herring, Andrew M, Vyas, Shubham, Maupin, C. Mark
Format: Article
Language:English
Subjects:
Chemistry
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Summary:Perfluorocyclobutyl polymers are thermally and chemically stable, may be produced without a catalyst via thermal 2π–2π cycloaddition, and can form block structures, making them suitable for commercialization of specialty polymers. Thermal 2π–2π cycloaddition is a rare reaction that begins in the singlet state and proceeds through a triplet intermediate to form an energetically stable four-membered ring in the singlet state. This reaction involves two changes in spin state and, thus, two spin-crossover transitions. Presented here are density functional theory calculations that evaluate the energetics and reaction mechanisms for the dimerizations of two different polyfluorinated precursors, 1,1,2-trifluoro-2-(trifluoromethoxy)­ethane and hexafluoropropylene. The spin-crossover transition states are thoroughly investigated, revealing important kinetics steps and an activation energy for the gas-phase cycloaddition of two hexafluoropropene molecules of 36.9 kcal/mol, which is in good agreement with the experimentally determined value of 34.3 kcal/mol. It is found that the first carbon–carbon bond formation is the rate-limiting step, followed by a rotation about the newly formed bond in the triplet state that results in the formation of the second carbon–carbon bond. Targeting the rotation of the C–C bond, a set of parameters were obtained that best produce high molecular weight polymers using this chemistry.
ISSN:0022-3263
1520-6904
DOI:10.1021/acs.joc.7b00597