LIGAND-DEPENDENT RELATIVE STABILITY ORDER IN ALLYL SULFIDE/PALLADIUM(O) SPECIES VS (ETA(3)-ALLYL)PALLADIUM(II) THIOLATE SPECIES

Oxidative additions of allyl phenyl sulfide and selenide to Pd-2(dba)(3) or Pd(MA)(COD) (dba = dibenzylideneacetone, MA = maleic anhydride, COD = cyclooctadiene) provided [Pd(eta(3)-C3H5)(EPh)](2)(E = S, Se) in good yields. Competitive reactions employing the sulfide and the selenide shouted the higher reactivity of the selenide with regard to oxidative addition. The reaction of [Pd(eta(3)-C3H5)(SPh)](2) with PR(3) afforded different types of products, depending on the nature of R and the molar ratio of the reagents. The reaction, with both 1 equiv and 2 equiv of PCy(3) (Cy = cyclohexyl) gave Pd(eta(3)-C3H5)(SPh)(PCy(3)) as the sole product. In the reactions with PPh(3) and P(OMe)(3), comparable amounts of the mu-allyl Pd-Pd complex Pd-2(mu-C3H5)(mu-SPh)(PR(3))(2) (R = Ph, OMe) and allyl phenyl sulfide were obtained in the case of PR(3)/Pd = 1, while the latter product predominated in the case of PR(3)/Pd > 3. Analogous reactions employing eta(3)-5-(methoxyycarbonyl)cyclohexenyl analogs and excess PPh(3) indicated that the formation of allyl phenyl sulfides took place with inversion of stereochemistry at the allylic carbon, suggesting exo attack of the thiolate at the eta(3)-allyl group in [Pd(eta(3)-allyl)-(PPh(3))(2)](+).