Issue 28, 2023

Forced topochemistry of a solid-state Diels–Alder reaction by encapsulation in epoxy glue

Abstract

We report on the solid-state Diels–Alder thermal reaction in a 1 : 1 charge-transfer (CT) crystal composed of bis(N-cyclobutylimino)-1,4-dithiin (the electron acceptor) and 9-bromoanthracene (the electron donor) which crystallized in the triclinic space group, P[1 with combining macron]. The donor (D) and acceptor (A) molecules arrange in stacks where these molecules alternate, where a full 9-bromoanthracene donor molecule is surrounded by a symmetrically different acceptor molecule on the two molecular faces. The distance between the reacting atoms on the donor and the two acceptor molecules are slightly different but still within Schmidt's criteria, resulting in two reaction sites with different reaction environments, assigned as regions P and Q. Molecules in region P are more favourably aligned with the distances between reacting atoms being 3.51 Å and almost parallel as the molecules overlap each other. In region Q, the distances are 3.56 and 3.86 Å because the molecular overlap is more skewed, and the reacting atoms are rotated −15° from each other. Initially, the reaction occurs only in region P until ∼20% conversion is reached. Afterward, product Q is concurrently formed but at a slower rate. After ∼75% reaction, the crystal transforms from triclinic P[1 with combining macron] into monoclinic C2/c, and conversion of ∼89% was found before the single crystal decomposes to become a powder. Reactions in free (unencapsulated) crystals above 10 °C were found to break apart during the initial reaction at around ∼20% when molecules in region P were reacting. Encapsulation of unreacted crystals with epoxy glue led to more reaction details being exposed and forced the reaction to occur topochemically until ∼89% conversion.

Graphical abstract: Forced topochemistry of a solid-state Diels–Alder reaction by encapsulation in epoxy glue

Supplementary files

Article information

Article type
Paper
Submitted
19 apr 2023
Accepted
23 maj 2023
First published
24 maj 2023
This article is Open Access
Creative Commons BY-NC license

CrystEngComm, 2023,25, 3988-3997

Forced topochemistry of a solid-state Diels–Alder reaction by encapsulation in epoxy glue

T. A. Lau, S. Khorasani and M. A. Fernandes, CrystEngComm, 2023, 25, 3988 DOI: 10.1039/D3CE00388D

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