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, [Pd 2 I 4 ][NBu 4 ] 2 , is generated in situ from Pd(OAc) 2 , Bu 4 NI, 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 (NBu 4 )], which, upon vinyl halide carbopalladation, forms products of cine -substitution by way of palladium(IV) carbenes, as corroborated by deuterium-labeling experiments.