Palladium(II) amido complexes with an unsymmetrical PNP′ pincer-type coordination and a new (E,E)-tetradentate diphosphinoazine coordination mode

Article abstract of DOI:10.1016/j.ica.2004.06.022

Cationic palladium(II) complexes [PdCl{PR₂CH ₂C(Bu^t)NNC(Bu^t)CH₂PR₂}] Cl (R=Prⁱ, c-C₆H₁₁, Bu^t) were synthesized. Their reactions with triethylamine gave complexes [PdCl{PR ₂CHC(Bu^t)NNC(Bu^t)CH₂PR ₂}], containing deprotonated diphosphinoazines in ene-hydrazone unsymmetrical pincer-like configuration which represent several of the still rare examples of Pd(II) amido bis(phosphine) complexes. A novel (E,E) tetradentate coordination mode of diphosphinoazines was also discovered. Cationic palladium(II) complexes [PdCl{PR₂CH₂C(Bu ^t)NNC(Bu^t)CH₂PR₂}]Cl, where R = isopropyl, cyclohexyl or tert-butyl, were synthesized by the reactions of the corresponding diphosphinoazines with bis(acetonitrile)palladium(II) dichloride. When bis(benzonitrile)palladium(II) dichloride was used instead, in the molar ratio of 2:1 to the diphosphinoazine, a new complex was isolated with the isopropyl ligand showing a previously unknown (E,E) tetradentate coordination mode. Crystal and molecular structure was determined by X-ray diffraction. The solid complex was a racemate of two axially chiral enantiomers and the chirality was preserved in solution. Reactions of the cationic complexes with triethylamine gave complexes [PdCl{PR₂CHC(Bu^t)NNC(Bu ^t)CH₂PR₂}], containing deprotonated diphosphinoazines in ene-hydrazone unsymmetrical pincer-like configuration. The complexes represent several of the still rare examples of Pd(II) amido bis(phosphine) complexes with a chlorine atom covalently bonded trans to the amide nitrogen.