Chemistry of bis(aryloxo)palladium(II) complexes with N-donor ligands: Structural features of the palladium-to-oxygen bond and formation of O-H center dot center dot center dot O bonds

Reaction of palladium acetate with 2 equiv of sodium phenoxide in the presence of a chelate diamine ligand affords the complexes [Pd(OPh)(2)(N similar to N)] (N similar to N = bpy (1), tmeda (2), teeda (3), dpe (4), dmap (5)). These yellow to orange bis(phenoxo)palladium(II) complexes are thermally stable at room temperature in the solid state as well as in solution. Addition of an excess of pentafluorophenol to 1, 2, 4, and 5 affords crystalline complexes [Pd(OC6F5)(2)(N similar to N)](N similar to N = bpy (6), tmeda (7), dpe (8), dmap (9)). Crystals of 1 and 6 have been subjected to X-ray diffraction studies. Crystals of 1 are orthorhombic, space group P2(1)2(1)2(1) (no. 19), with (1 = 6.7655(6) Angstrom, b = 16.0585(10) Angstrom, c = 16.7275(13) Angstrom, and Z = 4. Crystals of 6 are triclinic, space group <P(1)over bar > (no. 2), with a = 7.567(4) Angstrom, b = 12.708(3) Angstrom, c = 12.912(5) Angstrom, alpha = 61.51(3)degrees, beta = 74.74(4)degrees, gamma = 88.78(4)degrees, and Z = 2. The molecular structures of 1 and 6 show them to be square-planar complexes, and the main structural difference between these complexes is the orientation of the aromatic rings, In 6 the OC6F5 ligands are almost parallel in a face-to-face orientation (pi-pi stacking interactions), whereas in 1 the OC6H5 units are skewed away from each other. An unexpected ''mixed'' allcoxo(aryloxo) complex [Pd(OCH(CF3)(2))(OPh)(bpy)]. HOPh (10) is formed when 1 is reacted with 1,1,1,3,3,3-hexafluoro-2-propanol. The molecular structure of 10 shows O-H ... O hydrogen bonding (O . O = 2.642(8) Angstrom) between the hydroxyl hydrogen of phenol and the oxygen atom of the phenoxide ligand as well as an additional C-H ... O contact (C ... O) = 2.95(1) Angstrom), which can be regarded as the initial stage of a base-assisted beta-hydrogen elimination. Crystals of 10 are monoclinic, space group P2(1)/c, with a = 8.3241(14) Angstrom, b = 11.0316(17) Angstrom, c = 26.376(3) Angstrom, alpha = 93.01(1)degrees, Z = 4. Spectroscopic data of complexes 1-10 indicate that the oxygen atom of the aryloxide or alkoxide ligand is extremely electron-rich, leading to high polarization of the palladium-to-oxygen bond. The bis(phenoxide) complexes 1, 2, and 4 associate with two molecules of phenol through O-H ... O hydrogen bonds to form adducts [Pd(OPh)(2)(N similar to N)]. 2HOPh (N similar to N = bpy (11), tmeda (12), dpe (13)). The palladium complexes 6-9 with OC6F5 groups show no tendency to form adducts with alcohols.