Synthesis of novel heteroditopic carbene–pyridine palladium(II) chloro vinyl complexes. Comparative reactivity of different palladium vinyl derivatives toward transmetalation with alkynyl stannane

DeC-activated alkynes such as di-t-butyl-ethyne-dicarboxylate (DTA) or the more reactive dimethyl-ethynedicarboxylate (DMA) do not react with palladium(II) chloro methyl complexes bearing heteroditopic carbene–pyridine (C–N) as spectator ligands to give the corresponding vinyl derivatives. In order to prepare this type of derivatives we resorted to a dedicated synthetic protocol based on the displacement of labile pyridine-thioether ligands of vinyl palladium pyridine-thioeter species by the carbene–pyridine ligand of carbene–pyridine silver chloride complexes. However, the novel carbene–pyridine vinyl complexes obtained by such synthetic protocol, if compared with other palladium vinyl species with similar steric requirements, display a markedly reduced reactivity toward transmetalation with ethynyl-stannane