The unexpected case of reactions of halogens and interhalogens with halide substituted Pd(II) sigma-butadienyl complexes

We have experimentally studied and theoretically interpreted the addition under stoichiometric conditions of halogens or interhalogens to sigma-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 hypothesis based on a sequence of selective processes of oxidative addition and reductive elimination involving Pd(IV) intermediates.