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

Abstract

Heteroleptic palladium(II) complexes containing diphosphine(P∘P) and diamine (N∘N) ligands, [Pd(P∘P)(N∘N)](C1O₄)₂ (P∘P = bis(diphenylphosphino)ethane (dppe), bis(diphe-nylphosphino)propane (dppp), bis(diphenylphosphino)butane (dppb), and N∘N = 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(P∘P)Cl₂] and the appropriate diamine (N∘N). 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.

Key Words:

• Heteroleptic
• Palladium
• Diphosphine
• Diamine
• Conproportionation
• electrochemistry