Synthesis and characterisation of cyclometallated palladium(ii) complexes with phosphine–carboxylate and phosphine–amideligands

Abstract

The coordination properties of hybrid phosphino-amide ligands o-Ph₂PC₆H₄CONHR [R = ⁱPr (a), Ph (b)] have been investigated. New cyclometallated palladium(II) complexes in which a and b act as P-monodentate ligands have been synthesised by reacting them with selected cyclometallated precursors containing bridging chloride or acetate groups. The crystal structures of the compounds [Pd(Bzq)(o-Ph₂PC₆H₄CO–NHⁱPr)(Cl)] and [Pd(Phox)(o-Ph₂PC₆H₄CO–NHⁱPr)(CH₃COO)] (Bzq = 7,8-benzoquinolyl; Phox = 2-(2-oxazolinyl)phenyl) have been determined. Hemilability of coordinated ligand b is detected when it appears combined with certain cyclometallated backbones. A rigid P,O-chelating behaviour of the ligands, confirmed by the crystal structure determination of [Pd(Bzq)(o-Ph₂PC₆H₄CO–NHⁱPr)][PF₆], is observed in complexes obtained by adding stoichiometric KPF₆ to [Pd(C^N)(μ-Cl)]₂ compounds. The reactions of hydroxo-bridged precursors [Pd(C^N)(μ-OH)]₂ with a and b afforded mononuclear derivatives in which a less common anionic P,N-binding mode is exhibited. The crystal structure of Pd(Phpy)(o-Ph₂PC₆H₄CO–NⁱPr)] (Phpy = 2-phenylpyridine) is also reported. Furthermore, related compounds with phosphino-carboxylate ligands have been prepared by direct reaction between 2-(diphenylphosphinobenzoic) acid and [Pd(C^N)(μ-CH₃COO)]₂ precursors, and the X-ray structures of [Pd(C^N)(o-Ph₂PC₆H₄COO)] (C^N = Bzq and Phpy) have been determined.