Formate-Mediated\nReductive Cross-Coupling of Vinyl\nHalides and Aryl Iodides: <i>cine</i>-Substitution via Palladium(I)\nCatalysis

Formate-mediated reductive cross-couplings\nof vinyl halides with\naryl iodides via palladium(I) catalysis occur with highly uncommon <i>cine</i>-substitution. The active dianionic palladium(I) catalyst,\n[Pd<sub>2</sub>I<sub>4</sub>][NBu<sub>4</sub>]<sub>2</sub>, is generated <i>in situ</i> from Pd(OAc)<sub>2</sub>, Bu<sub>4</sub>NI, and\nformate. Oxidative addition of aryl iodide followed by dissociation\nof the dimer provides the monomeric anionic T-shaped arylpalladium(II)\nspecies, [Pd(Ar)(I)<sub>2</sub>(NBu<sub>4</sub>)], which, upon vinyl\nhalide carbopalladation, forms products of <i>cine</i>-substitution\nby way of palladium(IV) carbenes, as corroborated by deuterium-labeling\nexperiments.