Zinc-copper couple is a heterogeneous reagent prepared by treating zinc dust with a dilute copper(II) salt solution, resulting in a zinc surface coated with metallic copper. This treatment activates the zinc, significantly enhancing its reactivity as a reducing agent compared to zinc dust alone. Its primary application is in organic synthesis as a powerful and selective reducing agent. It is notably employed in the Simmons-Smith reaction for the cyclopropanation of alkenes, where it generates the active carbenoid species (ICH2ZnI) from diiodomethane. It is also used for the reductive dehalogenation of organic halides, particularly gem-dihalides and vicinal dihalides to alkenes, and for the reduction of nitro compounds and other functional groups under mild conditions. The zinc-copper couple is valued for its operational simplicity, cost-effectiveness, and the chemoselectivity it offers in various transformations. It is typically prepared in situ immediately before use due to its pyrophoric nature when dry, requiring careful handling under inert atmosphere.