Herein, we report that merging palladium catalysis with hydrogen atom transfer (HAT) photocatalysis enabled direct arylations and alkenylations of aldehyde C–H bonds, facilitating visible light-catalyzed construction of a variety of ketones. Tetrabutylammonium decatungstate and anthraquinone were found to act as synergistic HAT photocatalysts. Density functional theory calculations suggested a Pd0–PdII–PdIII–PdI–Pd0 pathway and revealed that regeneration of the Pd0 catalyst and the photocatalyst occurs simultaneously in the presence of KHCO3. This regeneration features a low energy barrier, promoting efficient coupling of the palladium catalytic cycle with the photocatalytic cycle. The work reported herein suggests great promise for further applications of HAT photocatalysis in palladium-catalyzed cross-coupling and C-H functionalization reactions to be successful.

Organocopper­(I) compounds are recognized as carbon nucleophiles, while organocopper­(III) complexes are involved in copper catalysis as intermediates to undergo a cross-coupling reaction with various anionic nucleophiles. In contrast to the chemistry of organocopper­(I) and (III) compounds, organocopper­(II) chemistry is virtually a missing link in integral organocopper chemistry because structurally well-defined organocopper­(II) compounds have barely been isolated or studied. We report in this Article an investigation of the radical reactions of stable and structurally well-defined arylcopper­(II) compounds, obtained readily from the arene CH bond reaction of macrocyclic azacalix[1]­arene[3]­pyridines and Cu­(ClO4)2. We have found that arylcopper­(II) compounds acted as essentially radical species to undergo an efficient three-component reaction with radical initiators 2,2′-azobis­(isobutyronitrile) (AIBN) or 2,2′-azobis­(2,4-dimethylvaleronitrile) (ABVN) and α,β-unsaturated compounds CH2CHX (X = CO2CH3, CN, CONH2, COCH3, and SO2Ph) to afford polyfunctionalized products. Combined experimental and theoretical studies revealed that radicals couple directly with the Caryl atom of arylcopper­(II) compounds to form CalkylCaryl bonds through a Cu­(II)/Cu­(I) mechanism. Comprehension of the formation and radical reactivity of arylcopper­(II) compounds has allowed the development of a copper-catalyzed three-component radical reaction for arene CH bond functionalization.

A nickel-catalyzed cross-electrophile coupling reaction between (hetero)­aryl bromides and 2,2-difluorovinyl tosylate is presented. This protocol provides facile incorporation of the gem-difluorovinyl moiety in organic molecules. The method features mild reaction conditions, good functional group tolerance, and excellent yields. Furthermore, mechanistic experiments and DFT studies indicate a Ni(0)/Ni­(II) catalytic cycle, thus differing from the currently accepted catalytic cycle for nickel-catalyzed C­(sp2)–C­(sp2) cross-electrophile coupling reactions.

A nickel-catalyzed enantioselective hydrocyanation of N-aryl 5-norbornene-endocis-2,3-dicarboximides was reported. This desymmetrization process allows for a quick construction of both continuous stereogenic carbon centers and remote N–CAr atropisomeric chirality. Mechanism studies indicated that the resident carbonyl group of the substrates plays a key role in the enantioselectivity.