Terminal and Bridging Bonding Modes of the Acetophenone Enolate to Palladium(II): The Structural Evidence and the Insertion of Isocyanides

The oxidative addition of PhCOCH2Cl to Pd(PPh3)4 led to a high yield of trans-[(PPh3)2(Cl)Pd(CH2COPh)], 3, in which the enolate is C-bonded to Pd(II), as shown by an X-ray analysis. Complex 3 reacts with ButNC., and depending on the stoichiometric ratio, two compounds were isolated. With a 1:1 stoichiometry, the insertion of ButNC into the PdC bond of 3 was observed and the crystalline solid 5 isolated, trans-[(PPh3)2(Cl)PdC-(NHBut)CHC(O) Ph], which contains the enolic form of a β-keto imino fragment. The reaction of 3 with 2 mol of ButNC led to a good yield (>70%) of an organic compound 7, which results from double insertion of ButNC on the PdC bond of 3, followed by homolytic cleavage of the PdC bond and dimerization of the resulting organic fragments. The ionization of the PdCl bond by AgCF3SO3 in acetonitrile led not to the cationic solvated form of 3, but rather to the dimer [{cis-(PPh3)2Pd}2(μ-CH2COPh)2]2+·2[CF3SO3]−, 9, containing the enolato anion bridging two palladium atoms in the oxoallyl form. In coordinating solvents, 9 is a source of the expected monomeric cationic form. Crystallographic details: 3 is monoclinic, space group Pn, a = 9.845(1) Å, b = 12.119(2) Å, c = 15.432(2) Å, α = γ = 90°, β = 95.29°, Z = 2, and R = 0.024; 5 is triclinic, space group P1̄, a = 12.040(1) Å, b = 18.473(2) Å, c = 11.922(1) Å, α = 97.25(1)°, β = 109.29(1)°, γ = 81.31°, Z = 8, and R = 0.072; 9 is monoclinic, space group I2/a, a = 21.550(2) Å, b = 34.773(3) Å, c = 22.592(2) Å, α = γ = 90°, β = 95.88(1)°, Z = 8, and R = 0.072.