Intraligand Charge Transfer Enables Visible‐Light‐Mediated Nickel‐Catalyzed Cross‐Coupling Reactions**

Abstract

We demonstrate that several visible-light-mediated carbonÀ heteroatom cross-coupling reactions can be carried out using a photoactive Ni II precatalyst that forms in situ from a nickel salt and a bipyridine ligand decorated with two carbazole groups (Ni(Czbpy)Cl 2 ). The activation of this precatalyst towards cross-coupling reactions follows a hitherto undisclosed mechanism that is different from previously reported light-responsive nickel complexes that undergo metalto-ligand charge transfer. Theoretical and spectroscopic investigations revealed that irradiation of Ni(Czbpy)Cl 2 with visible light causes an initial intraligand charge transfer event that triggers productive catalysis. Ligand polymerization affords a porous, recyclable organic polymer for heterogeneous nickel catalysis of cross-coupling reactions. The heterogeneous catalyst shows stable performance in a packed-bed flow reactor during a week of continuous operation.

Carbazolic Conjugated Microporous Polymers for Photocatalytic Organic Transformations

“…[100] Furthermore, Pieber and co-workers observed C-O, C-S, and C-N cross-coupling of nucleophiles with aryl halides by endowing czbpy-ligand sites over porous organic polymer(Ni@poly-Czbpy), affording the desired products in 62%, 88%, and 94% yield, respectively (Figure 10). [101] It was deduced that the irradiation of Ni(Czbpy)Cl 2 with visible light triggered intraligand charge transfer, leading to the effective catalysis. The Nicoordinated CMPs serve as recyclable heterogeneous catalyst for light-mediated carbon heteroatom cross-coupling reactions, which showed stable performance in seven days of continuous operation in a packed-bed reactor under flow mode condition.…”

“…Synthesis of Czbpy and Ni(Czbpy)Cl 2 and their application in C-O, C-S, and C-N cross-coupling of nucleophiles with aryl halides. Reproduced with permission [101]. Copyright 2019, Wiley-VCH.…”

Sodium-iodide-promoted nickel-catalyzed C–N cross-coupling of aryl chlorides andN-nucleophiles under visible-light irradiation

“…9 In contrast to the limited nucleophilic substrate scope of mild, light-promoted copper catalysis, visible-light single-nickel catalysis is well accommodated by a wide range of N -nucleophiles. 10 Various aryl iodides/activated aryl bromides can smoothly couple with diverse N -nucleophiles with broad functional group tolerance, but aryl chloride substrates and electron-rich aryl bromides still need further exploration in single-nickel photocatalysis (Scheme 1A).…”

“…Therefore, the development of a new approach to form C–N bonds by using readily available aryl chlorides and N -nucleophiles under mild conditions is of interest. Recently, inspired by light-promoted nickel-catalyzed aromatic halogen exchange and carbon-heteroatom bond formation, 10,11 we assumed that single-nickel catalysis probably can play two roles: halogen exchange and C–N coupling to access diverse C–N bonds by using aryl chlorides as coupling partners in the presence of visible light (Scheme 1A). Herein, we developed light-induced nickel catalysis for cross-couplings of aryl chlorides and N -nucleophiles using cheap abundant metal, commercially available ligands, and renewable solvents under mild conditions.…”

Programmable Photocatalytic Activity of Multicomponent Covalent Organic Frameworks Used as Metallaphotocatalysts

“…Seminal approaches include the incorporation of nickel atoms into carbon nitride materials,[ 18 , 19 , 20 , 21 ] and a conjugated microporous polymer that contains a bipyridine motif in its repeating unit that can ligate nickel atoms. [ 22 , 23 ] However, these ill‐defined macrostructures do not allow for detailed structure‐activity relationship studies to better understand the underlying processes, which renders knowledge‐guided improvement of the bifunctional materials difficult.…”