Synthesis of novel palladium allyl complexes bearing heteroditiopic NHC-S ligands. Kinetic study on the carbene exchange between bis-carbene palladium allyl complexes

摘要

We have synthesized several novel palladium allyl and 1,1-dimethylallyl complexes bearing differentudheteroditopic NHCeS ligands giving rise to a five-membered chelate ring with the metal center.We wereudable to synthesize some homoleptic bis-carbene allyl derivatives by taking advantage of the hemilabilityudof the thioetheric sulfur. Attempts at preparing mixed bis-carbene complexes bearing two differentudheteroditopic carbenes (i.e. NHCeS and NHCePy) simultaneously coordinated to the palladium centerudlead to a carbene transmetalation with the formation of a statistically distributed equilibrium mixture ofudthe two pure homoleptic and of the mixed bis-carbene palladium allyl complexes in solution. In twouddifferent cases the rate of the equilibrium reaction was measured and a mechanistic hypothesis provided.udFinally, we have determined the solid state structures of a complex bearing only one NHCeS heteroditopicudcarbene and of the bis-carbene (NHCeS, NHCePy) palladium allyl derivatives.