BINDING OF ETHYLENE TO ANIONIC, NEUTRAL, AND CATIONIC NICKEL(II), PALLADIUM(II), AND PLATINUM(II) CIS TRANS CHLORIDE AMMONIA COMPLEXES - A THEORETICAL-STUDY/

Calculations using the hybrid density functional method B3LYP have bee n performed on square-planar, group X metal complexes of the type (C2H 4)MClx(NH3)(3-x) (M = Ni(II), Pd(II), or Pt(II); x = 1, 2, or 3). Gene rally, the ability to coordinate ethylene is in the expected order Pt > Pd > Ni. In line with the abundance of reported anionic, neutral, an d cationic alkene complexes of Pt, the bonds between Pt and ethylene a re strong and rather independent of the charge on the complexes, and b ond energies range from 33.9 to 46.1 kcal/mol. For Ni, the situation i s different. The never-observed anionic (C2H4)NiCl3- coordinates ethyl ene weakly (6.1 kcal/mol), whereas the still not observed cationic (C2 H4)NiCl(NH3)(2)(+) shows a reasonably strong intrinsic coordination (2 5.2 kcal/mol). A significant degree of pi-back-donation is observed fo r all three metals, the order being Pt > Pd > Ni. However, for each me tal, the pi-back-donation is independent of charge. In all cases where comparisons are possible, Cl- exerts a stronger trans influence on et hylene than NH3.