Aerobic Cross-dehydrogenative Coupling Reaction Research Articles

Triangulenium Ions: Versatile Organic Photoredox Catalysts for Green-Light-Mediated Reactions

AbstractThe development of tunable organic photoredox catalysts remains important in the field of photoredox catalysis. A highly modular and tunable family of trianguleniums (azadioxatriangulenium, diazaoxatriangulenium, and triazatriangulenium), and the related [4]helicene quinacridinium have been used as organic photoredox catalysts for photoreductions and photooxidations under visible light irradiation (λ = 518–640 nm). A highlight of this family of photoredox catalysts is their readily tunable redox properties, leading to different reactivities. We report their use as photocatalysts for the aerobic oxidative hydroxylation of arylboronic acids and the aerobic cross-dehydrogenative coupling reaction of N-phenyl-1,2,3,5-tetrahydroisoquinoline with nitromethane through reductive quenching. Furthermore, their potential as photoreduction catalysts has been demonstrated through the catalysis of an intermolecular atom-transfer radical addition via oxidative quenching. These transformations serve as benchmarks to highlight that the easily synthesized trianguleniums, congeners of the acridiniums, are versatile organic photoredox catalysts with applications in both photooxidations and photoreductions.

Structural Engineering of Two-Dimensional Covalent Organic Frameworks for Visible-Light-Driven Organic Transformations.

Covalent organic frameworks (COFs) emerging as a novel kind of visible light-responsive organic semiconductor have attracted extensive research attention in the field of photocatalytic organic transformations. However, the key parameters affecting their photocatalytic properties are still not clear. In this work, a series of [3 + 3] COFs with similar two-dimensional hexagonal structure but different compositions are synthesized and employed as model materials for investigating the key factors affecting the photocatalytic properties in the visible-light-driven reductive dehalogenation reaction and the aerobic cross-dehydrogenative coupling reaction. In comparison with -H and -CF3, the -OH substituent in the aromatic ring could narrow the band gap of the COFs. The COFs with a triazine skeleton in the framework usually boost the photocatalytic activity, possibly because of the enhanced charge separation efficiency by the formation of a donor-acceptor domain. As a combined result of the narrow band gap, efficient charge separation, and high conductivity, the COF possessing both a -OH group and triazine skeleton shows the highest activity in the photocatalytic reductive dehalogenation reaction. Notably, COFs could be easily recovered and reused several times without the loss of crystallinity. Our primary results may shed light on the design of efficient COF-based semiconductors for photocatalytic organic transformations.

Sulfuryl chloride as an efficient initiator for the metal-free aerobic cross-dehydrogenative coupling reaction of tertiary amines.

A metal-free cross-dehydrogenative (CDC) reaction of tertiary amines was developed using a catalytic amount of sulfuryl chloride (SO2Cl2) under mild aerobic conditions. On the basis of the nature of SO2Cl2, it was assumed that the reagent acts as a radical initiator to induce the metal-free CDC reaction via a radical-initiated autoxidation mechanism.

Computational Studies on the Mechanism of the Copper-Catalyzed sp3 -CH Cross-Dehydrogenative Coupling Reaction.

A detailed computational study of a copper-catalyzed aerobic cross-dehydrogenative coupling reaction has been conducted. To select a reliable method to describe the thermochemistry of a single electron transfer (SET) process, benchmark calculations have been performed. M06/6-311+g(d,p) is appropriate to evaluate the thermochemistry of the SET process for the system involving iminium species. The computational results support an SET mechanism, but also uncover an alternative mechanism in which O2 is directly involved in a hydrogen-abstracting step. A comparative study with tert-butylhydroperoxide (TBHP) as the oxidant has also been performed. The computations reveal several competitive pathways, including a radical pathway, a CuIII pathway, and an SET mechanism for the Cu/TBHP system.

Graphene-Supported RuO2 Nanoparticles for Efficient Aerobic Cross-Dehydrogenative Coupling Reaction in Water

A cross-dehydrogenative coupling (CDC) reaction between tertiary amines and nitroalkanes has been realized under an oxygen atmosphere in water simply by using graphene-supported RuO(2) as the catalyst, which was made from water-soluble graphene with sulfonic groups and RuCl(3)·nH(2)O to form RuO(2)·nH(2)O nanocomposites in situ. In contrast to RuCl(3)·nH(2)O and RuO(2)·nH(2)O, the graphene-supported RuO(2) nanoparticles exhibited higher activity and stability for the aerobic CDC reaction in water.

Catalytic aerobic production of imines en route to mild, green, and concise derivatizations of amines

The development of a general, mild, and chemoselective catalytic aerobic oxidation of amines to imines is described. The combination of a less sterically demanding and electron-deficient new N-oxyl radical (ketoABNO: 5) and copper(I) salt is key for the high catalytic activity and allows for the use of molecular oxygen as the stoichiometric oxidant producing H2O as the sole side-product. The novel method is extendable to a direct α-derivatization of secondary amines via sequential aerobic oxidation of amines to imines followed by C–C bond-formation to the resulting imines, including the novel catalytic asymmetric aerobic cross-dehydrogenative coupling reaction. Mechanistic insight into the novel catalytic system is also discussed.