The layered structures of graphite and related nanographene molecules play key roles in their physical and electronic functions. However, the stacking modes of negatively curved nanographenes remains unclear, owing to the lack of suitable nanographene molecules. Herein we report the synthesis and one-dimensional supramolecular self-assembly of negatively curved nanographenes without any assembly-assisting substituents. This curved nanographene self-assembles in various organic solvents and acts as an efficient gelator. The formation of nanofibers was confirmed by microscopic measurements, and an unprecedented double-helix assembly by continuous π-π stacking was uncovered by three-dimensional electron crystallography. This work not only reports the discovery of an all-sp 2-carbon supramolecular π-organogelator with negative curvature, but also demonstrates the power of three-dimensional electron crystallography for the structural determination of submicrometer-sized molecular alignment. File list (4) download file view on ChemRxiv KatoWNGgel_ChemRxiv.pdf (4.62 MiB) download file view on ChemRxiv TOC_KatoWNGgel.png (833.97 KiB) download file view on ChemRxiv SI_KatoWNGgel_ChemRxiv.pdf (3.78 MiB) download file view on ChemRxiv CIF_KatoWNGgel.cif (2.36 MiB)
A convenient asymmetric reductive amination of benzylic ketones (α-arylated ketones) catalyzed by newly designed Cp*Ir complexes bearing a chiral N-(2-picolyl)sulfonamidato ligand was developed. Using readily available β-amino alcohols as chiral aminating agents, a range of benzo-fused and acyclic ketones were successfully reduced with formic acid in methanol at 40 °C to afford amines with favorable chemo- and diastereoselectivities. The amino alcohol-derived chiral auxiliary was easily removed by mild periodic oxidants, leading to optically active primary β-arylamines without erosion of the optical purity (up to 97% ee). The excellent catalytic performance was retained even upon lowering the amount of catalyst to a substrate/catalyst (S/C) ratio of 20,000, and the amination could be performed on a large scale exceeding 100 g. The precise hydride transfer to iminium species generated from the ketonic substrate and the chiral amine counterpart was suggested by the mechanistic studies on stoichiometric reactions of isolable hydridoiridium complexes and model intermediates such as N,O-acetal, enamine, and iminium compounds.
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