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 R-1-C equivalent to CCH(R-2)NMe(R-3) and thioethers R-1-C equivalent to CCH(R-2)SR4 (R-1 = Me, n-Bu, Ph; R-2 = H, Me; R-3 = Me, bn; and R-4 = Me, i-Pr, Ph) with Li2PdCl4 in methanol affords the air-stable five-membered palladocyclic compounds [Pd-C(R-1)=C-(C-1)CH(R-2)NMe(R-3)(u-Cl)](2) and [Pd-C(R-1)=C(Cl)CH(R-2)SR4(u-Cl)](2), respectively, resulting formally from the trans nucleophilic addition of the chlorine anion onto the C equivalent to C bond. On the other hand, alkynes with more sterically demanding groups (R-1 = t-Bu or SiMe3) only form adducts of the type PdCl2(alkyne)(2). Under the same reaction conditions, the terminal alkynes (R-1 = 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.