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 been performed on square-planar, group X metal complexes of the type (C2H4)MClx(NH3)(3-x) (M = Ni(II), Pd(II), or Pt(II); x = 1, 2, or 3). Generally, the ability to coordinate ethylene is in the expected order Pt > Pd > Ni. In line with the abundance of reported anionic, neutral, and cationic alkene complexes of Pt, the bonds between Pt and ethylene are strong and rather independent of the charge on the complexes, and bond energies range from 33.9 to 46.1 kcal/mol. For Ni, the situation is different. The never-observed anionic (C2H4)NiCl3- coordinates ethylene weakly (6.1 kcal/mol), whereas the still not observed cationic (C2H4)NiCl(NH3)(2)(+) shows a reasonably strong intrinsic coordination (25.2 kcal/mol). A significant degree of pi-back-donation is observed for all three metals, the order being Pt > Pd > Ni. However, for each metal, the pi-back-donation is independent of charge. In all cases where comparisons are possible, Cl- exerts a stronger trans influence on ethylene than NH3.