Chemistry of chelate-stabilized aryloxopalladium(II) complexes:: syntheses, X-ray crystal structures and formation of C-H•••O hydrogen-bonds

In this paper the synthesis, characterization and properties of various Pd(II) complexes with 2-acylphenolates as chelating ligands are reported. The compounds are easily accessible by stirring 2-acylphenoles with Pd(II) complexes in the presence of potassium tert-butoxide. Cyclometallated tri(o-tolyl)phosphine derivatives and allyl palladium complexes were chosen as palladium precursor. The solid state structures of the complexes 2-acetylphenolato-[o-(di-o-tolylphosphino)benzyl]palladium(II) (2), 2-benzoylphenolato-[o-(di-o-tolylphosphino)benzyl]palladium(II) (4) and 2-acetyl-1-naphtholato-[o-(di-o-tolylphosphino)benzyl]palladium(II) (6) were further studied by X-ray diffraction analyses. In all complexes the palladium center is coordinated in a square planar fashion. Interestingly, coordination of the 2-acylphenolates to palladium results in a significant perturbation of the delocalization within the aromatic ring. The strong hydrogen-bond acceptor behavior of the phenolic oxygen as well as the cis/trans-isomerisation is discussed in terms of the solid structure (2, 4 and 6) and the NMR shifts observed in various solvents. (C) 1998 Elsevier Science Ltd. All rights reserved.