Palladium(II) complexes of chiral tridentate nitrogen pybox ligands

A series of mono- and di-cationic palladium(II) complexes containing different chiral tridentate nitrogen ligands, pybox, have been prepared [pybox = 2,6-bis[4'-(S)-Pr-i (or Ph, or Bz or p-EtOC(6)H(4))oxazoline-2'-yl]pyridine (1-4), respectively]. The molecular structures for two of these, [Pd(CH3CN(2)](BF4)(2) (6) and [Pd(PPh(3)(3)](BF4)(2) (21g), have been determined by X-ray diffraction and show no major steric hindrance in the fourth coordination position. In connection with the aldol reaction of CNCH(2)CO(2)Me with PhCHO, several new isonitrile Pd-II complexes have also been prepared. It is shown that, under catalytic conditions, the chiral tridentate pybox ligand is completely displaced, thus explaining its failure as a chiral auxiliary. Preparative details for a series of chiral Pd(L)(3)(n+)(BF4)(n) (21) complexes [L = 4-methylpyridine, 2,6-dimethylpyridine, 4-methyl aniline, H2NCH2CH(OMe)(2), H2NCH2CH2OH, H2N(CH2)(5)CH3, N-3(-), HCO2-, Cl-] are given, as are preparative details for some model Pd-II acetonitrile complexes with chiral phosphorus and nitrogen chelating ligands. For 6, i.e. PdC25H22N4O2B2F8, the crystals are monoclinic with space group P2(1) (No. 4), a = 13.582(6) Angstrom, b = 13.826(6) Angstrom, c = 14.667(6) Angstrom, beta = 97.28(3)degrees, V = 2732(2) Angstrom(3), Z = 4. For 21g, i.e. C43H38B2F8N3O2P2Pd, the crystals are orthorhombic with space group, P2(1)2(1)2(1), a = 10.616(4) Angstrom, b = 16.774(2) Angstrom, c = 23.086(4) Angstrom, V = 4111(3) Angstrom(3), Z = 4.