Pyrazolato-bridged arylpalladium(II) complexes, [Pd2Ar2(μ-pz/dmpz)2(PR3)2]: Synthesis and characterization

The reactions of [Pd2Ar2(μ-Cl)2(PR3)2] with pyrazole or 3,5-dimethylpyrazole in the presence of methanolic sodium hydroxide yield pyrazolato-bridged binuclear arylpalladium complexes, [Pd2Ar2(μ-pz′)2(PR3)2] (Ar = Ph or C6H4Me-4 (tol); pz′ = pz or dmpz; PR3 = PEt3, PMe2Ph). These complexes exist exclusively in sym-trans form both in solution (by NMR) and in the solid state (by X-ray). The molecular structures of [Pd2tol2(μ-Cl)2(PMe2Ph)2], [Pd2tol2(μ-pz)2(PMe2Ph)2] and [Pd2tol2(μ-dmpz)2(PEt3)2] have been established by X-ray diffraction analyses. The former is a centrosymmetric dimer while the latter two adopt a boat like conformation. The Pd⋯Pd separation in pyrazolato-bridged complexes is influenced by steric demands of particular pyrazolato-ligand.