COORDINATION CHEMISTRY AND MECHANISMS OF METAL-CATALYZED CC-COUPLING REACTIONS .7. HECK VINYLATION OF ARYL HALIDES WITH N-BUTYL ACRYLATE - RELEVANCE OF PC BOND-CLEAVAGE TO CATALYST DEACTIVATION

The Heck reaction between aryl halides ArX (X = Br, Cl) and n-butyl acrylate was studied in the presence of catalyst systems containing Pd(OAc)(2) and a tertiary phosphine ligand (PR(3), R(2)P-(CH2)-PR(2)). It is shown that all tested arylphosphines except P(o-Tol)(3) and P(Mes)(3) undergo an extensive PC bond cleavage at temperatures higher than 120 degrees C. As a consequence, vinylic side products are formed with concomitant catalyst deactivation. In the case of triarylphosphines side products originate from reaction intermediates of the type Pd-II(PAr3)(2)(Ar)X. These species undergo an aryl-aryl exchange between the palladium center and coordinated phosphine ligands. Subsequent intermolecular phosphine scrambling leads to several isomerized arylpalladium species, all of which couple with n-butyl acrylate to give the corresponding cinnamic ester side products.