Steric and Electronic Effects on Arylphosphonate Elimination from Organopalladium Complexes

To study the effects of electronic and steric manipulation of metal-bound aryl fragments on arylphosphonate formation, model organopalladium complexes have been prepared and investigated. While no phosphorus−carbon bond formation was observed at 25 °C, all of the arylpalladium phosphonates underwent clean reductive elimination in C6D6 solutions at elevated temperatures. The incorporation of electron-donating groups into the metal-bound aryl fragments accelerated the elimination process, while palladium complexes containing aryl groups with electron-withdrawing or ortho substituents exhibited slower elimination rates. While the rate of arylphosphonate formation was dependent upon the nature of the metal-bound aryl fragment, it was rather insensitive to the identity of the phosphonate moiety. These results demonstrate the results of subtle changes in the electronic and steric composition of the eliminating species in P(O)−C bond-forming reactions.