Conversion of Imine to Oxazole and Thiazole Linkages in Covalent Organic Frameworks

Abstract
Imine-linked ILCOF-1 based on 1,4-phenylenediamine and 1,3,6,8-tetrakis(4-formylphenyl)pyrene was converted through consecutive linker substitution and oxidative cyclization to two isostructural covalent organic frameworks (COFs), having thiazole and oxazole linkages. The completeness of the conversion was assessed by infrared and solid-state NMR spectroscopies, and the crystallinity of the COFs was confirmed by powder X-ray diffraction. Furthermore, the azole-linked COFs remain porous, as shown by nitrogen sorption experiments. The materials derived in this way demonstrate increased chemical stability, relative to the imine-linked starting material. This constitutes a facile method for accessing COFs and linkages that are otherwise difficult to crystallize due to their inherently limited microscopic reversibility.

Citation
Waller, P. J., AlFaraj, Y. S., Diercks, C. S., Jarenwattananon, N. N., & Yaghi, O. M. (2018). Conversion of Imine to Oxazole and Thiazole Linkages in Covalent Organic Frameworks. Journal of the American Chemical Society, 140(29), 9099–9103. doi:10.1021/jacs.8b05830

Acknowledgements
This work was supported by the Army Research Office through a Multidisciplinary University Research Initiatives (MURI) Award through Grant WG11NF-15-1-0047. P.J.W. additionally thanks the NSF and the Berkeley Center for Green Chemistry for support via the Systems Approach to Green Energy Integrative Graduate Education and Research Traineeship (1144885). Y.S.F. is supported by the Gifted Student Program Scholarship through the King Abdullah University of Science and Technology. C.S.D. acknowledges funding through a Kavli ENSI Philomathia Graduate Student Fellowship. The authors thank Dr. Chenfei Zhao, Mary E. Garner and Robinson W. Flaig for helpful discussions.

Publisher
American Chemical Society (ACS)

Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY

DOI
10.1021/jacs.8b05830

Additional Links
https://pubs.acs.org/doi/10.1021/jacs.8b05830

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