The trans-Chloropalladation Reaction of Propargyl Amines and Thioethers. X-ray Crystal Structure of trans-[Pd-trans-C(Ph)C(Cl)CH(Me)S(i-Pr)(Cl)(Py)]

The reaction of the propargyl amines R¹C⋮CCH(R²)NMe(R³) and thioethers R¹C⋮CCH(R²)SR⁴ (R¹= Me, n-Bu, Ph; R² = H, Me; R³ = Me, bn; and R⁴ = Me, i-Pr, Ph) with Li₂PdCl₄ in methanol affords the air-stable five-membered palladocyclic compounds [PdC(R¹)C(Cl)CH(R²)NMe(R³)(μ-Cl)]₂ and [PdC(R¹)C(Cl)CH(R²)SR⁴(μ-Cl)]₂, respectively, resulting formally from the trans nucleophilic addition of the chlorine anion onto the C⋮C bond. On the other hand, alkynes with more sterically demanding groups (R¹ = t-Bu or SiMe₃) only form adducts of the type PdCl₂(alkyne)₂. Under the same reaction conditions, the terminal alkynes (R¹ = H) afford analogous five-membered palladocyclic compounds in very low yields and an ill-defined mixture of organic/organometallic products. However, the treatment of these terminal alkynes with catalytic amounts of palladium(II) salts and copper dichloride in the presence of lithium chloride and water yields (2-chloroallyl)amines and thioethers in good yields.