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2020-09-07 - QuinoneHel - ChemRxiv.pdf (4.66 MB)
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MicroED Elucidation of Diverse Solid-State Packing in a Family of Electron-Deficient Expanded Helicenes

preprint
revised on 10.09.2020 and posted on 10.09.2020 by Adrian Samkian, Gavin R. Kiel, Christopher G. Jones, Harrison Bergman, Julia Oktawiec, Hosea Nelson, T. Don Tilley
Solid-state packing plays a defining role in the properties of a molecular organic material, but it is difficult to elucidate in the absence of single crystals that are suitable for X-ray diffraction. Here, we demonstrate the coupling of divergent synthesis with microcrystal electron diffraction (MicroED) for rapid assessment of solid-state packing motifs, using a class of chiral nanocarbons – expanded helicenes – as a proof of concept. Two highly selective oxidative dearomatizations of a readily-accessible helicene provided a divergent route to four electron-deficient analogues containing quinone or quinoxaline units. Crystallization efforts consistently yielded microcrystals that were unsuitable for single crystal X-ray diffraction, but ideal for MicroED. This technique facilitated the elucidation of solid-state structures of all five compounds with <1.1 Å resolution. The otherwise-inaccessible data revealed a range of notable packing behavior, including four different space groups, homochirality in a crystal for a helicene with an extremely low enantiomerization barrier, and nanometer scale cavities. The results of this study suggest that MicroED will soon become an indispensable tool for high-throughput investigations in pursuit of next-generation organic materials.

Funding

NSF #CHE-1708210

NSF #DGE-1650604

NIH #S10OD023532

NIH-NIGMS #P30 GM124165

NIH-ORIP HEI #S10 RR029205

DOE #DE-FC02-02ER63421

History

Email Address of Submitting Author

asamkian@caltech.edu

Institution

University of California, Berkeley

Country

United States

ORCID For Submitting Author

0000-0002-0068-3572

Declaration of Conflict of Interest

No conflict of interest

Version Notes

version 1.0

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