Formate-Mediated Reductive Cross-Coupling of Vinyl Halides and Aryl Iodides: cine-Substitution via Palladium(I) Catalysis

Formate-mediated reductive cross-couplings of vinyl halides with aryl iodides via palladium­(I) catalysis occur with highly uncommon cine-substitution. The active dianionic palladium­(I) catalyst, [Pd2I4]­[NBu4]2, is generated in situ from Pd­(OAc)2, Bu4NI, and formate. Oxidative addition of aryl iodide followed by dissociation of the dimer provides the monomeric anionic T-shaped arylpalladium­(II) species, [Pd­(Ar)­(I)2(NBu4)], which, upon vinyl halide carbopalladation, forms products of cine-substitution by way of palladium­(IV) carbenes, as corroborated by deuterium-labeling experiments.