Air stable, phosphine-free anionic palladacyclopentadienyl catalysts: Remarkable halide and pseudohalide effects in Stille coupling

The Stille cross-coupling of allylic and benzyl bromides is shown to proceed efficiently using phosphine-free dinuclear anionic palladacyclopentadienyl catalysts possessing bridging (N,O)-imidate ligands. The type of bridging anion influences the catalytic activity considerably. Halide anions such as chloride, bromide or iodide also influence the catalytic activity but to a far lesser extent than the pseudohalide imidate anions (from succinimide or phthalimide). A Baldwin-type cooperative effect is seen with 7a using CuI as a co-catalyst, in the presence of two equivalents of CsF in DMF at 40 °C. In toluene, these additives slow down substrate turnover.