Synthesis and characterization of mono- and dinuclear aryl palladium(II) complexes: oxidative additions of 1,4-dihalogenated benzene or 4,4′-dibromobiphenyl to Pd(PR3)4

Abstract

Mononuclear palladium(II) complexes 1–12, (C6H4X-4)PdXʹ(PR3)2 (X = I, Br, or Cl; Xʹ = I or Br; R = Ph, Cy, Et, or Me), were synthesized by oxidative addition of 1,4-dihalogenated benzene to Pd(PR3)4; dinuclear palladium(II) complexes 13–15, (Me3P)2XPd(C6H4-1,4)PdXʹ(PMe3)2 (X, Xʹ = I or Br), could be obtained only using trimethylphosphine. Another method to prepare 13–15 is via re-oxidative addition of the corresponding mononuclear palladium(II) complexes and Pd(PMe3)4. Using 4,4′-dibromobiphenyl as the starting material, the mononuclear palladium(II) complexes [C6H4(C6H4Br-4)-4]PdBr(PPh3)2 (16) and [C6H4(C6H4Br-4)-4]PdBr(PCy3)2 (17) with bulky phosphines could be synthesized at relative low temperature, while dinuclear 18, (Cy3P)2BrPd(C6H4C6H4-4,4ʹ)PdBr(PCy3)2, was prepared by bis-oxidative addition at higher temperature. The re-oxidative addition of 16 and Pd(PMe3)4 gave dinuclear 19, (Me3P)2BrPd(C6H4C6H4-4,4ʹ)PdBr(PMe3)2, accompanying phosphine exchange. X-ray diffraction analysis revealed that formation of dinuclear palladium(II) complexes depends on the reaction temperature, phosphine ligands, and bridging groups.