Donor-Acceptor Boron-Ketoiminate Complexes with Pendent N-Heterocyclic Arms: Switched-on Luminescence through N-Heterocycle Methylation

Lozada, Issiah B.; Ortiz, Robert J.; Braun, Jason D.; Williams, J.A. Gareth; Herbert, David E.

doi:10.1021/acs.joc.1c02138

Donor-Acceptor Boron-Ketoiminate Complexes with Pendent N-Heterocyclic Arms: Switched-on Luminescence through N-Heterocycle Methylation

Lozada, Issiah B.; Ortiz, Robert J.; Braun, Jason D.; Williams, J.A. Gareth; Herbert, David E.

Authors

Issiah B. Lozada

Robert J. Ortiz

Jason D. Braun

Professor Gareth Williams j.a.g.williams@durham.ac.uk
Professor

David E. Herbert

Abstract

A series of intramolecular, donor-stabilized BF2 complexes supported by phenanthridinyl-decorated, β-ketoiminate chelating ligand scaffolds is described, along with their characterization by spectroscopy and X-ray diffraction. In solution, the relative orientation of the pendent phenanthridinyl arm is fixed despite not coordinating to the boron center, and a well-resolved through-space interaction between a phenanthridinyl C–H and a single fluorine atom can be observed by 19F–1H NOE NMR spectroscopy. The neutral compounds are nonetheless only weakly luminescent in fluid solution, ascribed to nonradiative decay pathways enabled by rotation of the N-heterocyclic unit. Methylation of the phenanthridinyl nitrogen restricts this rotation, “switching on” comparably strong emission in solution. Modeling by density functional theory (DFT) and time-dependent DFT (TDDFT) indicates that the character of the lowest energy excitation changes upon methylation, with shallow calculated potential energy surfaces of the neutral complexes consistent with their lack of significant radiative decay.

Citation

Lozada, I. B., Ortiz, R. J., Braun, J. D., Williams, J. G., & Herbert, D. E. (2022). Donor-Acceptor Boron-Ketoiminate Complexes with Pendent N-Heterocyclic Arms: Switched-on Luminescence through N-Heterocycle Methylation. Journal of Organic Chemistry, 87(1), 184-196. https://doi.org/10.1021/acs.joc.1c02138

Journal Article Type	Article
Acceptance Date	Dec 8, 2021
Online Publication Date	Dec 22, 2021
Publication Date	Jan 7, 2022
Deposit Date	Mar 10, 2022
Publicly Available Date	Dec 22, 2022
Journal	Journal of Organic Chemistry
Print ISSN	0022-3263
Electronic ISSN	1520-6904
Publisher	American Chemical Society
Peer Reviewed	Peer Reviewed
Volume	87
Issue	1
Pages	184-196
DOI	https://doi.org/10.1021/acs.joc.1c02138

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Copyright Statement
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Organic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.joc.1c02138.