Nickel Photoredox/Dual-Catalyzed Transfer Semi-Hydrogenation of Alkynes via Aminoalkyl Nickel Species

Using amines in catalytic transfer hydrogenation (TH) is challenging, despite their potential availability as a hydrogen source. Here, we describe a photoredox/nickel-catalyzed TH of alkyne through an intermediary aminoalkyl Ni species. This reaction successfully provided functionalized (Z)-alkenes, such as (homo)allyl ethers, alcohols, and amides (Z/E = up to >99:1), and the reaction thus bypasses a limitation of substrate scope in TH using amine and a Lindlar catalyst. Mechanistic studies revealed that the aminoalkyl Ni species plausibly participates in two catalyst regeneration paths: (1) β-hydride elimination followed by reductive elimination and (2) protodemetalation from alkenyl Ni^I.