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DOI: 10.1055/a-2707-4673
Sterically Driven Pathways in Schiff Base Formation: tert-Butyl Effects on Hindered Imines
Authors
Funding InformationThis project was supported by the Scientific and Technological Research Council of Türkiye (TÜBİTAK) and the National Science Foundation (NSF) regarding the 2501 - Joint Support Program with NSF research grant (Project No: 122N411).
Abstract
The ZnCl2/AcOH-mediated condensation of acenaphthenequinone with 2,4,6-tri-tert-butylaniline was explored to prepare a sterically demanding bidentate α-diimine ligand. Contrary to expectation, the reaction consistently afforded 1,2-bis[(2,4-di-tert-butylphenyl)imino]acenaphthene as the major product, together with a mono-substituted imino-ketone, while the fully substituted 1,2-bis[(2,4,6-tri-tert-butylphenyl)imino]acenaphthene was detected only in trace amounts. Spectroscopic analysis (nuclear magnetic resonance, UV/vis, Fourier transform infrared spectroscopy and single-crystal X-ray diffraction, supported by density functional theory calculations, showed that both ligands possess nearly identical electronic structures. However, the additional ortho tert-butyl group in the tri-substituted analogue induces severe steric congestion, twisting the aryl–imine geometry, diminishing π-conjugation, and facilitating acid-promoted tert-butyl elimination. In contrast, the di-substituted ligand adopts a near-planar geometry, enabling straightforward synthesis, crystallization, and full characterization. These results demonstrate that steric effects override electronic factors in dictating the reactivity and stability of highly hindered Schiff bases, providing mechanistic insight and practical design principles for the development of robust, sterically encumbered ligands in coordination chemistry and catalysis.
Keywords
Schiff bases - Steric hindrance - tert-Butyl elimination - Bidentate acenaphthenes - Sterically encumbered ligandsAuthor Contributions
M.M.C. is the only author who created, wrote, and contributed to this work. All data were generated in-house, and no paper mill was used. The author agrees to be accountable for all aspects of work ensuring integrity and accuracy.
Publication History
Received: 13 August 2025
Accepted after revision: 17 September 2025
Accepted Manuscript online:
23 September 2025
Article published online:
22 October 2025
© 2025. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution License, permitting unrestricted use, distribution, and reproduction so long as the original work is properly cited. (https://creativecommons.org/licenses/by/4.0/).
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