SYNTHESIS AND CHARACTERIZATION OF HETEROLEPTIC PALLADIUM(II) COMPLEXES CONTAINING DIPHOSPHINE AND DIAMINE LIGANDS

Abstract

Heteroleptic palladium(II) complexes containing diphosphine(PˆP) and diamine (NˆN) ligands, [Pd(PˆP)(NˆN)](C1O4)2 (PˆP = bis(diphenylphosphino)ethane (dppe), bis(diphe-nylphosphino)propane (dppp), bis(diphenylphosphino)butane (dppb), and NˆN = ethyle-nediamine(en), propylenediamine (pn), butylenediamine (bn), 1,2-phenylenediamine (Øn), 4-methyl-1,2-phenylenediamine (4-Me-Øn), 4-chloro-l,2-phenylenediamine (4-Cl-Øn) and 4-nitro-l,2-phenylenediamine (4-NO2-Øn)) were synthesized from the complexes [Pd(PˆP)Cl2] and the appropriate diamine (NˆN). These mixed-ligand complexes were characterized by spectroscopic measurements (IR, electronic, 1H and 31P nmr) and electrochemical properties. The 31P nmr of the complexes were considerably different depending on the diphosphine ligands, while the contribution of diamines to the spectra is quite small. The electronic absorption maximum of Pd(II)-dppp which has stronger backbonding in comparison to Pd(II)-dppe or Pd(II)-dppb appeared at lowest energy. Redox potentials and peak currents of the complexes were not much influenced by the various diphosphine and diamine ligands. [Pd(dppe)(en)]2+, [Pd(dppe)(4-Me-Øn)]2+ and [Pd(dppp)(en)]2+ were also prepared by conproportionation reactions from ethylenedia-mine (or 4-Me-Øn) and the appropriate diphosphine complexes and could be identified by voltammetry.