Mechanisms of 1,1-Reductive Elimination from Palladium: Coupling of Styrylmethylpalladium Complexes

Article abstract of DOI:10.1021/ja00404a033

The complexes (E)- and (Z)-styrylbromobis(triphenylphosphine)palladium(II) <(E)- and (Z)-1a> react with methyllithium in benzene at ambient temperature to give (E)- and (Z)-propenylbenzene, respectively.A similar reaction at -78 deg C afforded (E)- and (Z)-styrylmethylbis(diphenylmethylphosphine)palladium(II) <(E)- and (Z)-2b> as a cis-trans mixture.On raising the temperature of solutions of (E)- and (Z)-2b, (E)- and (Z)-propenylbenzenes are produced, respectively, and the intermediate olefin complexes (E)- and (Z)-propenylbenzenebis(diphenylmethylphosphine)palladium(0) <(E)- and (Z)-3b> can be observed by NMR the reductive elimination reaction is intramolecular as determined by a crossover experiment and first order in dialkylpalladium(II) complex when diphenylmethylphosphine is present.The reaction of (E)-2b and trideuteriomethyl iodide gives some 3,3,3-trideuteriopropenylbenzene, again implicating a palladium(IV) intermediate as a possible reductive elimination intermediate in a catalytic coupling cycle.