Photoexcited Ni^II–Aryl Complex-Mediated Giese Reaction of Aryl Bromides

Abstract

A Giese reaction of aryl bromides with electrondeficient alkenes was developed, enabled by a dual catalyst system containing Ni II complex and Ir III photocatalyst. This protocol could accommodate a variety of aryl bromides and electron-deficient alkenes, delivering the conjugate adducts in up to 97% yield. The utilization of photoexcited (dtbbpy)Ni II (aryl)Br intermediate as an aryl radical source allows this novel transformation of aryl halides, thus expanding the chemical space of excited nickel catalysis.

Visible-Light-Induced Nickel-Catalyzed Cross-Coupling of Aryl Bromides with Nitriles

“…Based on our experimental results and previous reports, − a plausible reaction mechanism is proposed as shown in Scheme . Initially, (dtbbpy)­Ni II Br 2 I was reduced by the photoexcited HE* to deliver the real catalyst species (dtbbpy)­Ni I Br II .…”

“…In 2018, Doyle and co-workers reported the direct photoexcitation of a Ni II –aryl halide complex, without the assistance of other photocatalyst, could lead to the homolysis of the Ni–aryl bond, which indicates the Ni–aryl complex could be utilized as a convenient aryl radical precursor under photocatalysis . Very recently, our group developed a photoexcited Ni II –aryl complex-mediated Giese reaction of aryl bromide with electron-deficient alkene, in which the in situ formed aryl radicals were trapped with alkenes . Building off this work, we questioned if a radical addition of the aryl radical, generated from homolysis of the excited Ni II –aryl halide complex, with a nitrile would enable a new platform for the synthesis of an aryl ketone (Scheme b).…”

Generation and Application of Aryl Radicals Under Photoinduced Conditions

“…An additive ( HE ) is used to generate iridum(II) required for removing bromide from nickel complex (Figure 29, Table 1T). [50] In this work, a dual catalyst system composed of a Ni(II) complex and an Ir(III) photocatalyst facilitated the reaction of aryl bromides with electron‐deficient alkenes. The reaction started with the oxidative addition of aryl bromide with the Ni(II)‐complex, which was later reduced by photoactivated HE.…”

Photoredox/Nickel Dual Catalysis-Enabled Cross-Dehydrogenative C–H Amination of Indoles with Unactivated Amine

“…On the basis of the mechanistic studies and other reports, a plausible mechanism is proposed in Scheme . Under visible-light irradiation, the photocatalyst was photoexcited into excited state *­[Ir­(dF­(CF 3 )­ppy) 2 (dtbbpy)]­[PF 6 ], which underwent a SET process with N -methylindole 1a to generate the radical cation intermediate II and the corresponding Ir II species.…”