Synthesis and characterization of cyclometallated palladium(II) complexes with 2-(diphenylphosphino)benzaldehyde

Abstract

New palladium(II) complexes containing 2-(diphenylphosphino)benzaldehyde a (Ph2P(o-C6H4CHO), displaying different coordination modes, have been synthesized in moderate to good yields (62–91%). The cyclometallated palladium(II) complexes [Pd(C^N)(Ph2 P(o-C6H4CHO)(Cl)] (1–4) in which a is P-monodentate have been prepared by reacting it with selected cyclometallated precursors containing bridging chlorides [Pd(C^N)(μ-Cl)]2 [C^N=2-phenylpyridine (Phpy), 7,8-benzoquinoline (Bzq), azobenzene (Phazo), and 2-phenyloxazoline (Phox), respectively]. A rigid P,O-chelating behavior of a, confirmed by the crystal structure determination of [Pd(Phox)(Ph2 P (o-C6H4CHO)][CF3SO3] (8), is observed in complexes (5–8) obtained by adding AgCF3SO3 in 2: 1 ratio to [Pd(C^N)(μ-Cl)]2 precursors. NMR spectroscopy helped identify the proposed coordination modes, with noticeable shifts of resonances upon chelation: upfield in the case of 31P and CHO in 1H, downfield for the C=O signal in 13C NMR. All the new complexes have been characterized by partial elemental analyses and spectroscopic methods (IR, fast atom bombardment, 1H, 13C, 19F, and 31P NMR).