Convenient Synthesis of Cationic (eta-3-allyl)palladium Complexes - Preparative and Stereochemical Aspects

The oxidative addition of allylic trifluoroacetates to Pd(dba)2 (dba = dibenzylideneacetone) gives (eta-3-allyl)palladium trifluoroacetates in excellent yields. The stereochemistry of the reaction is solvent dependent; i.e., predominant trans addition is observed in a THF/MeCN mixture, whereas cis addition dominates in pure THF. By addition of a neutral ligand the trifluoroacetates can be converted to cationic complexes either directly (giving trifluoroacetate salts) or by in situ ion exchange with tetrafluoroboric acid (giving tetrafluoroborate salts). The syn-anti stereochemistry of the cationic eta-3-allyl complexes can be largely controlled by the use of the hindered ligand 2,9-dimethyl-1,10-phenanthroline under the appropriate preparative conditions. Cationic complexes with phenanthroline ligands can also be prepared in good yields by acid-assisted oxidative addition of allylic acetates and alcohols to Pd(dba)2.