Synthesis and characterisation of cyclometallated palladium(II) complexes with phosphine–carboxylate and phosphine–amide ligands

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)(oPh2PC6H4CO–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 phosphinocarboxylate 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.