Reactivity of [Pd3(μ-OAc)3(μ,η2-MeSCHCO2Et-C,S)3] in the presence of triphenylphosphine: a model of the early steps of the Pd/PR3-catalysed Heck reaction

The stable complex [Pd(η1-OAc)(η2-MeSCHCO2Et-C,S)(PPh3)] (2) is readily formed by addition of triphenylphosphine to [Pd3(μ-OAc)3(μ,η2-MeSCHCO2Et-C,S)3] (1:1 P:Pd) in acetone. It crystallizes in the monoclinic space group C2/c, with Z=8, a=145.08(2), b=109.82(1), c=306.33(3) pm and β=96.3(1)°, R(F)=0.026, Rw (F2)=0.0765. The coordination of a second triphenylphosphine to the palladium atom leads to [Pd(η1-OAc){CH(SMe)CO2Et}(PPh3)2] (3). Whereas 2 appears to be remarkably stable, 3, after a slow reductive elimination, evolves mainly to [Pd(η2-MeSCHCO2Et-C,S)(PPh3)2]−. Zero-valent palladium species can also be generated by electrochemical reduction of 3. The rate constant for the oxidative addition of iodobenzene to the electrogenerated palladium(0) species has been estimated.