Bis-amides and Amine Bis-amides as Ligands for Olefin Polymerization Catalysts Based on V(IV), Cr(IV) and Mn(IV). A Combined Density Functional Theory and Valence Bond Study.
 
  Tim Firman and Tom Ziegler Department of Chemistry, University of Calgary, 2500 University Drive N. W., T2N 1N4 Calgary, Alberta, Canada Density functional theory (DFT) calculations have been carried out on the ability of (NH₂)₂MR(+) (M=V,Cr,Mn,Mo,Ru,Pd; R=C₂H₅) to act as olefin polymerization catalysts. It is concluded that the second row metals which form low spin complexes are poor catalysts with high barriers of activation ( ~ 25 kcal mol^-1). The first row transition metals form high spin complexes with barriers of insertion given by (kcal mol^-1) 9.5 (V), 6.3 (Cr) and 11.1 (Mn), respectively. For the more promising chromium system the barrier of termination is 13.3 kcal mol^-1. Adding an amine ligand to form (NH₂)₂NH₃MR(+) (M=V,Cr,Mn) has the effect of increasing especially the termination barrier. The most promising candidate is (NH₂)₂NH₃VR(+) with an insertion barrier of 8.3 kcal mol^-1 and a termination barrier of 16.4 kcal mol^-1. Designs are suggested that bridge the nitrogen atoms to form bi- and tri- dentate ligands. The calculated trends are interpreted in terms of concepts based on valence bond theory.