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Elucidation of Diverse Solid‐State Packing in a Family of Electron‐Deficient Expanded Helicenes via Microcrystal Electron Diffraction (MicroED) **
Author(s) -
Samkian Adrian E.,
Kiel Gavin R.,
Jones Christopher G.,
Bergman Harrison M.,
Oktawiec Julia,
Nelson Hosea M.,
Tilley T. Don
Publication year - 2021
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.202012213
Subject(s) - helicene , crystallography , electron diffraction , chemistry , homochirality , electron crystallography , solid state , crystallization , diffraction , electron , materials science , chemical physics , nanotechnology , enantiomer , stereochemistry , molecule , organic chemistry , physics , optics , quantum mechanics
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. Herein, 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 behaviors, including four different space groups, homochirality in a crystal for a helicene with an extremely low enantiomerization barrier, and nanometer scale cavities.