Evidence that SCS pincer Pd(II) complexes are only precatalysts in Heck catalysis and the implications for catalyst recovery and reuse

SCS-pincer Pd(II) complexes have been covalently immobilized onto porous silica, cross-linked polymer (Merrifield resin) and soluble poly(norbornene) supports via either amide or urea linkages and evaluated in the Heck coupling of iodobenzene with n-butyl acrylate. Kinetic experiments and poisoning studies indicate that in all cases the pincer complexes merely act as precatalysts. Contrary to literature reports, there is no evidence for catalysis by the intact amide-linked SCS-Pd(II) complexes under any conditions studied here.