title: Flexible diphosphine ligands with overall charges of 0, +1, and +2: critical role of the electrostatics in favoring trans over cis coordination.
abstract: The influence of the formal electrostatic interaction on the cis/trans coordination mode at a PdCl(2) center is investigated in a family of isostructural flexible diphosphine ligands Ph(2)P-X-C(6)H(4)-Y-PPh(2), where X and Y stand for neutral or cationic N,C-imidazolylene linkers. While the neutral and monocationic diphosphine spontaneously behave as classical cis-chelating ligands, only the dicationic diphosphine, where the electrostatic repulsion between the formal positive charges specifically takes place, is observed to behave as a trans-chelating ligand. The crucial role of electrostatics is analyzed on the basis of (31)P NMR data in solution and X-ray diffraction data in the crystal state. Comparative theoretical studies of the cis- and trans-chelated complexes, including EDA, static (31)P NMR, MESP, and AIM analyses, have been undertaken on the basis of DFT calculations in the gas phase or in the acetonitrile continuum. Whereas the cis-coordination mode is shown to be thermodynamically favored for the neutral ligand, the trans-coordination mode is found to be preferred for the dicationic homologue. The stereochemical preference is thus shown to be parallel to the expected effect of the formal electrostatic interaction. The results open perspectives for control of the cis- and trans-chelating behavior of flexible bidentate ligands by more or less reversible charge transfer at the periphery of the coordination sphere of a metallic center.
authors: CNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de Narbonne, F-31077 Toulouse, France. yves.canac@lcc-toulouse.fr
authors: Yves
authors: Y
authors: Canac
authors: Nathalie
authors: N
authors: Debono
authors: Christine
authors: C
authors: Lepetit
authors: Carine
authors: C
authors: Duhayon
authors: Remi
authors: R
authors: Chauvin
mesh_terms: D002384:Catalysis; D002614:Chelating Agents / Q000032:analysis / Q000138:chemical synthesis*; D015392:Chemistry, Inorganic / Q000379:methods*; D018360:Crystallography, X-Ray; D007093:Imidazoles / Q000032:analysis / Q000138:chemical synthesis*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds; D010165:Palladium / Q000737:chemistry*; D010720:Phosphines / Q000032:analysis / Q000138:chemical synthesis*; D012996:Solutions; D055672:Static Electricity; D013237:Stereoisomerism; D013816:Thermodynamics
chemical_list: D002614:Chelating Agents; D007093:Imidazoles; D008024:Ligands; D009942:Organometallic Compounds; D010720:Phosphines; D012996:Solutions; D010165:Palladium; C008756:palladium chloride