Ammonium Complexes of Orthoester Cryptands Are Inherently Dynamic and Adaptive

Wang, Xiang; Shyshov, Oleksandr; Han�eva?ki, Marko; J�ger, Christof M.; Von Delius, Max

Abstract

© 2019 American Chemical Society. Fluxional chemical species such as bullvalene have been a valuable source of inspiration and fundamental insight into the nature of chemical bonds. A supramolecular analogue of bullvalene, i.e., a "fluxional host-guest system", in which the ensemble of a well-defined host and guest is engaged in continuous, degenerate constitutional rearrangements, is still elusive, however. Here, we report experimental and computational evidence for guest-induced dynamic covalent rearrangements in the ammonium complexes of self-assembled orthoester cryptands. This unique behavior is made possible by the ammonium guest playing a dual role: it is sufficiently acidic to initiate dynamic covalent exchange reactions at the orthoester bridgeheads, and as a hydrogen bond donor it acts as a supramolecular template, governing the outcome of a multitude of possible intra- and intermolecular rearrangement reactions. One particularly striking example of inherent dynamic behavior was observed in host-guest complex [NH4+o-Me2-2.1.1], which spontaneously rearranged into the larger and thermodynamically more stable complex [NH4+o-Me2-2.2.1], even though this process led to the formation of poor host o-Me2-1.1.1 as a consequence of the excess of one subcomponent (diethylene glycol; "1" in our nomenclature). These inherently adaptive host-guest networks represent a unique platform for exploring the interrelationship between kinetic and thermodynamic stability. For instance, as a result of optimal NH4+ binding, complex [NH4+o-Me2-2.2.1] was found to be thermodynamically stable (negligible intermolecular rearrangements over weeks), whereas computational studies indicate that the compound is far from kinetically stable (intramolecular rearrangements).

Citation

Wang, X., Shyshov, O., Hanževački, M., Jäger, C. M., & Von Delius, M. (2019). Ammonium Complexes of Orthoester Cryptands Are Inherently Dynamic and Adaptive. Journal of the American Chemical Society, 141(22), 8868-8876. https://doi.org/10.1021/jacs.9b01350

• Journal Article Type: Article
• Acceptance Date: May 22, 2019
• Online Publication Date: May 22, 2019
• Publication Date: Jun 5, 2019
• Deposit Date: May 31, 2019
• Publicly Available Date: May 23, 2020
• Journal: Journal of the American Chemical Society
• Print ISSN: 0002-7863
• Electronic ISSN: 1520-5126
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 141
• Issue: 22
• Pages: 8868-8876
• DOI: https://doi.org/10.1021/jacs.9b01350
• Public URL: https://nottingham-repository.worktribe.com/output/2116037
• Publisher URL: https://pubs.acs.org/doi/10.1021/jacs.9b01350
• Additional Information: This paper is also linked to the High Performance Computing Centre
• Contract Date: May 31, 2019