Binding of polar monomers in the complexes with organometallic ethylene polymerization catalysts - Natural orbitals for chemical valence and energy decomposition analysis

作者：Srebro Monika; Mitoraj Mariusz; Michalak Artur^*

来源：Canadian Journal of Chemistry, 2009, 87(7): 1039-1054.

DOI：10.1139/V09-072

• NOCV
• bonding analysis
• donor-acceptor properties
• copolymerization of olefins with polar monomers
• single-site catalysts

The binding mode of polar monomers in complexes with late-transition-metal catalysts for ethylene polymerization was studied by density functional theory (DFT) calculations. The Ziegler-Rauk energy decomposition scheme was used to characterize the geometry distortion and steric and orbital-interaction terms in the bonding energy, while Natural Orbitals for Chemical Valence (NOCV) were applied to describe the donation and back-bonding components of the bond between the monomer and the catalyst. The NOCV analysis allowed for comparison of the donor-acceptor properties of different monomers in the sigma- and pi-complexes. The complexes with the model, cationic Ni- or Pd-diimine catalysts, N boolean AND N-Ni(H)+ and N boolean AND N-Pd(H)+, and the neutral Ni-anilinotropone system, N boolean AND O-Ni(H), were investigated. The monomers studied included: simple olefins (Et and Pr); examples of oxygen- and nitrogen-containing polar monomers (methyl acrylate (MA), vinyl acetate (VAc), their fluorinated derivatives (FMA, FVAc), vinyl ether (VE), acrylonitrile (AN), and beta-butenoic nitrile (BN); vinyl and allyl amines (VAm, PrAm); and a tertiary dimethyl vinyl amine (MVAm). The results demonstrate that the metal-based fragment has a significant influence on the relative stability of the sigma- and pi-complexes; the pi-binding mode increases in the following order: N boolean AND N-Ni(H)+ < N boolean AND N-Pd(H)+ < N boolean AND O-Ni(H). The results of the Ziegler-Rauk bond-energy decomposition indicate that for some monomers (MA, FMA, VAc, AN, VAm, MVAm) the preference of the coordination mode has a steric (electrostatic and Pauli) origin. For other monomers (VE, FVAc, BN, PrAm) the changes in the orbital-interaction terms are important as well. The results of the NOCV analysis indicate that for both, sigma- and pi-coordination modes there exist components describing sigma-donation and pi-back-bonding. The sequences of sigma-donor and pi-acceptor properties of monomers in the pi-complexes as well as sigma-complexes are similar for the considered catalysts.

• 出版日期2009-7