Reactivity of [Pd-3(mu-OAc)(3)(mu,eta(2)-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(h1-OAc)(h2-MeSCHCO2Et-C,S)(PPh3)] (2) is readily formed by addition of triphenylphosphine to [Pd3(m-OAc)3(m,h2-MeSCHCO2Et-C,S)3] (1:1 P:Pd) in acetone. It crystallizes in the monoclinic space group C2:c, with Z8, a145.08(2), b109.82(1), c306.33(3) pm and b96.3(1)°, R(F)0.026, Rw (F2)0.0765. The coordination of a second triphenylphosphine to the palladium atom leads to [Pd(h1-OAc){CH(SMe)CO2Et}(PPh3)2] (3). Whereas 2 appears to be remarkably stable, 3, after a slow reductive elimination, evolves mainly to [Pd(h2-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.