interhalogens to σ-butadienyl palladium complexes bearing the heteroditopic thioquinolines as spectator ligands. The observed reactions do not involve the expected extrusion of the butadienyl fragment but rather the unpredictable substitution of the halide coordinated to palladium and in some cases also of that bound to the terminal butadienyl carbon. We have explained this peculiar reactivity with a mechanistic
E)−σ−butadienyl and the pyridylthioether palladium(II) dibromide species. The rates of these reactions have been determined. When the interhalogens are used as oxidizing agents the thermodynamically hampered species is formed at first. Only in the case of the reaction of IBr is the formation of the energetically hampered derivative followed by partial isomerization to the most stable complex. The rate of isomerization