Computer Design of Living Olefin Polymerization Catalysts: A Combined Density Functional Theory and Molecular Mechanics Study

Abstract

Ethylene polymerization catalyzed by group-4 diamide complexes has been studied by molecular modeling. The modeling was based on pure density functional theory (DFT) in the case of the generic [RNCH2CH2CH2NR]MCH2CH2CH3+ complexes with R = H and M = Ti, Zr, and Hf. For the substituted systems with R = 2,6-iPr2C6H3 and M = Ti and Zr, a combined DFT and molecular mechanics (MM) scheme (QM/MM) was employed. The generic systems revealed the following trends with respect to the three group-4 metals: ethylene complexation energies are Ti (19.2 kcal/mol) < Hf (21.3 kcal/mol) ≤ Zr (22.0 kcal/mol); the overall insertion barriers ΔE⧧insertion are Zr (7.4 kcal/mol) ≤ Ti (8.1 kcal/mol) < Hf (9.6 kcal/mol); and the chain termination barriers, ΔE⧧termination, relative to the most stable π complexes are Hf (8.1 kcal/mol) ≈ Zr (8.2 kcal/mol) < Ti (10.3 kcal/mol). The QM/MM calculations on the substituted systems gave the following energies: for ethylene complexation 17.0 (Ti) and 22.4 (Zr) kcal/mol; for the insertion ba...