Origin for Fluxional Structure of Tetracoordinate Pd~(II) Complexes

摘要

In the Pd-catalyzed cross-coupling reactions, the PdL2 complexes with the bulky and electron-rich L ligands (phos-phines, NHCs, etc) are important compounds as a Pd~((0))(L)_n-precusor.1 The catalytic activity of Pd~((0))(L)_n-precusors was influenced by the electronic property of the strong σ-donor and the steric effect of the bulky L ligands. Due to the electron-transfer from the strong σ-donor L ligand to Pd, the oxidation state of Pd in the neutral [Pd~((0))L_nX] catalysts is zerovalent.In some X-ray crystallography results, the Pd([9]aneB2A)L2 complexes with mixed hard/soft tridentate ligand have been observed as a five-coordinate geometry with an apical (soft A···Pd~(II)) interaction. In Pd~((0))(η~2,η~2,η~2-C_(10)H_(16)N2Me2) complexes with an aza-macrocyclic ligand, the six coordination bonds of the three olefin units with Pd were symmetrically formed via three (olefin···Pd~(II)) interactions. Meanwhile, in hydration reactions on square planar [PdCl4]~(2-) complexes, two vertical (H2O···Pd~(II)) and(HOH··· Pd~(II)) interactions for the ligand exchange processes were investigated theoretically and experimentally. With increasing the strength of the fifth (solvent ···Pd~(II)) interaction, the replacement of the equatorial (Pd-Cl) bond with (solvent···Pd~(II)) takes place via a five-coordinate transition states.