Silica and polymer-tethered Pd–SCS-pincer complexes: evidence for precatalyst decomposition to form soluble catalytic species in Mizoroki–Heck chemistry

Palladium(II)–SCS-pincer complexes have been covalently immobilized on porous silica and polynorbornene supports and evaluated in the Mizoroki–Heck reaction of iodobenzene and n-butyl acrylate. Kinetic experiments and poisoning studies indicate that the pincer complexes decompose under reaction conditions via rupture of the palladiumligand bonds to liberate active Pd(0) homogeneous species. There is no evidence for catalysis by the intact Pd(II) pincer complex under any conditions evaluated, ruling out a Pd(II)–Pd(IV) catalytic mechanism that has been postulated for palladacycle catalysts under the conditions used here.