C–N Cross-Coupling via Photoexcitation of Nickel–Amine Complexes

Abstract

C-N cross-coupling is an important class of reactions with far-reaching impacts across chemistry, materials science, biology, and medicine. Transition metal complexes can elegantly orchestrate diverse aminations but typically require demanding reaction conditions, precious metal catalysts, or oxygen-sensitive procedures. Here, we introduce a mild nickel-catalyzed C-N cross-coupling methodology that operates at room temperature using an inexpensive nickel source (NiBr·3HO), is oxygen tolerant, and proceeds through direct irradiation of the nickel-amine complex. This operationally robust process was employed for the synthesis of diverse C-N-coupled products (40 examples) by irradiating a solution containing an amine, an aryl halide, and a catalytic amount of NiBr·3HO with a commercially available 365 nm LED at room temperature without added photoredox catalyst and the amine substrate serving additional roles as the ligands and base. Density functional theory calculations and kinetic isotope effect experiments were performed to elucidate the observed C-N cross-coupling reactivity.

Energy‐Efficient Solar Photochemistry with Luminescent Solar Concentrator Based Photomicroreactors

“…This effect can be attributed to the decreased UV content of the light reaching the reaction channels in the LSC-PM. [30] Since the primary application of the LSC-PM is in solar photochemistry,w ep erformed some reactions with natural sunlight. Because of its simplicity and safety,the first reaction selected for outdoor testing on al arger scale was the photooxidation of methionine (Figure 3).…”

Light‐Promoted Nickel Catalysis: Etherification of Aryl Electrophiles with Alcohols Catalyzed by a NiII‐Aryl Complex

“…The simple, abundant methanol afforded 21 in good yield, thereby opening a route to anisole derivatives. [6i] Primary aliphatic alcohols bearing benzylic and branched structures (23-25) as well as pendant trifluoroethanol (22), per-fluorobutylethanol (26), alkenyl (27, 28), amino (30), furan-2-yl (32), and thiophen-2-yl (33) groups were also good coupling substrates. It is worth noting that the catalyst was not poisoned by the coordinative amino and thiophen moieties.…”

“…Irradiation of A at 390-395 nm would excite the Ni II complex to a 3 MLCT state [21] that probably decays to a long-lived 3 d-d state, which could then undergo homolysis of the nickel À carbon bond to generate Ni I and aryl radicals. [14d] The former could then react with the aryl halide to generate a Ni III -Ar intermediate, which would undergo facile reductive elimination upon ligand exchange with the alcohol (presumably facilitated by DBU), [22] affording the coupled ether product while regenerating the Ni I . Continuous irradiation is necessary.…”

Photochemical Strategies for Carbon–Heteroatom Bond Formation

“…A photocatalyst‐free amination through direct sensitization of nickel complexes with UV‐light was also reported (Scheme ) . The coupling of aryl halides ( 12 ) with a series of primary and secondary amines ( 34 ) was proposed to start by coordination of two to three amine molecules to NiBr 2 · H 2 O.…”