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Our study unveils a novel approach to accessing boryl radicals through the spontaneous homolytic cleavage of B-B bonds. We synthesized a hexaaryl-substituted diboron(6) dianion, 1, via the reductive B-B coupling of 9-borafluorene. Intriguingly, compound 1 exhibits the ability to undergo homolytic B-B bond cleavage, leading to the formation of boryl radical anions, as confirmed by EPR studies, in the presence of the 2.2.2-cryptand at room temperature. Moreover, it directly reacts with diphenylacetylene, producing an unprecedented 1,6-diborylated allene species, where the phenyl ring is dearomatized. Density functional theory computational studies suggest that homolytic B-B bond cleavage is favored in the reaction path, and the formation of the boryl radical anion is crucial for dearomatization. Additionally, it achieves the dearomative diborylation of anthracene and the activation of elemental sulfur/selenium under mild conditions. The borylation products have been successfully characterized by NMR spectra, HRMS, and X-ray single-crystal diffraction.

Direct arene C–H functionalization by amidyl radicals for arylamides synthesis has made significant advances. While photocatalytic protocols can offer easy generation of amidyl radicals under mild conditions, designing catalysts involving earth-abundant Fe complexes for C–H amidation is an attractive approach to bring about ligand-enabled selectivity control. However, due to preference for high-spin configuration, designing robust Fe catalysts for C–H amidation remains a substantial challenge. Taking the advantage of the strong Cp–Fe linkages, here we developed the 17-electron ferrocenium complexes as effective catalysts for facile intramolecular aryl C–H amidation with 1,4,2-dioxazol-5-one as amidyl radical precursors. The ferrocenium-catalyzed reaction affords 3,4-dihydroquinolin-2(1H)-ones in excellent yields and selectivity. Our experimental and computational studies revealed that the intramolecular arene amidation is brought about by electrophilic arene addition by reactive Fe(IV)-amidyl radical species. Consistent with the experimental findings, the regioselectivity (ipso- versus ortho-amidyl radical addition) is influenced by electronic factors. The ipso amidyl radical addition should form an azaspirocyclohexadienyl radical intermediate. Subsequent radical-polar crossover and 1,2-alkyl migration followed by rearomatization afforded the skeletal rearranged dihydroquinolinone lactams. A recyclable heterogeneous amidation catalyst has been prepared by grafting ferrocene onto commercially available silica, and comparable catalytic activities with the homogeneous system were observed.

This study explores a bottom-up approach toward negatively curved carbon allotropes from octabenzo[8]circulene, a negatively curved nanographene. Stepwise chemical reduction reactions of octabenzo[8]circulene with alkali metals lead to a unique highly reduced hydrocarbon pentaanion, which is revealed by X-ray crystallography suggesting a local view for the reduction and alkali metal intercalation processes of negatively curved carbon allotropes. Polymerization of the tetrabromo derivative of octabenzo[8]circulene by the nickel-mediated Yamamoto coupling reaction results in a new type of porous carbon-rich material, which consists of a covalent network of negatively curved nanographenes. It has a specific surface area of 732 m2 g-1 and functions as anode material for lithium ion batteries exhibiting a maximum capacity of 830 mAh·g-1 at a current density of 100 mA·g-1. These results indicate that this covalent network presents the key structural and functional features of negatively curved carbon allotropes. ©