DFT study of olefin versus nitrogen bonding in the coordination of nitrogen-containing polar monomers to diimine and salicylaldiminato nickel (II) and palladium(II) complexes. Implications for copolymerization of olefins with nitrogen-containing polar monomers

Organometallics

Volumn 21, Issue 8, 2002, Pages 1603-1611

  Deubel, Dirk V ^a   Ziegler, Tom ^a  

^a UNIVERSITY OF CALGARY   (Canada)

Author keywords

[No Author keywords available]

Indexed keywords

POLAR MONOMERS;

BINDING ENERGY; CATALYSTS; CHEMICAL BONDS; COMPLEXATION; COORDINATION REACTIONS; COPOLYMERIZATION; MONOMERS; NITROGEN; OLEFINS;

ORGANOMETALLICS;

EID: 0000064766     PISSN: 02767333     EISSN: None     Source Type: Journal    
DOI: 10.1021/om010662c     Document Type: Article

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44. This approach significantly reduces the number of conformational degrees of freedom which have been considered in our computational study. We have investigated one case with a real nonconjugated monomer (X = CN, n = 1, with the Brookhart Ni catalyst, 1) to show that our approximation is justified. The calculated energy for π coordination is -18.7 kcal/mol, and the calculated energy for N coordination is -30.4 kcal/mol. The corresponding values with the abbreviated models are -18.3 kcal/mol (1b) and -28.3 kcal/mol (1g), respectively (Table 1). The results demonstrate that the differences are relatively small and our approach is warranted.
45. 16
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53. Note that Figure 5 oversimplifies the nature of the chemical bond. In complexes and chemical reactions of transition-metal compounds, there are several orbitals of the metal fragment that contribute to the interactions. For example, see: Deubel, D. V.; Frenking, G. J. Am. Chem. Soc. 1999, 121, 2021.
54. We have performed a fragment-based population analysis of the complexes 1a,c,e and 2a,c,e to demonstrate the interactions shown in Figure 5. The formation of the ethylene complex la from ethylene and the catalyst 1 leads to an electron loss in the occupied orbitals of ethylene (-0.44 e) and to an electron gain in the vacant orbitals of 1 (+0.49 e). These values are a measure of donation d from ethylene to the catalyst. The occupied orbitals of 1 lose fewer electrons (-0.30 e) and the vacant orbitals of ethylene gain a similar amount (+0.24 e), indicating that back-donation b from the Brookhart catalyst to the olefin is much weaker than donation. In contrast, donation and back-donation in the Grubbs ethylene complex 2a are of same strength (d = -0.37, +0.42; b = -0.36, +0.32). The population analysis also reflects the electron-withdrawing effect of the nitrile substituent in the complexes 1c (d = -0.39, +0.45; b = -0.40, +0.33) and 2c (d = -0.31, +0.37; b = -0.50, +0.43) as well as the electron-releasing effect of the amine moieties in le (d = -0.49, +0.51; b = -0.16, +0.15) and 2e (d = -0.42, +0.45; b = -0.33, +0.27).
55. The energy of the oxygen lone pairs of methyl acrylate (-6.8 eV) is given in ref 16 and can be compared to the lone pairs of the nitrogen-containing systems (Table 5). It is interesting to note that the lone-pair energy of the nitriles is lower and the lone-pair energy of the amines is higher than the value of methyl acrylate. Since both N-containing monomers form stronger bonds with the Brookhart catalyst than does the O-containing system, lone-pair energies are unsuitable to elucidate the stabilization energies. We have performed additional energy-decomposition analyses of the complexes 1g,h,j-4g,h,j for comparison with the analyses of the methyl acrylate complexes in ref 16. The results are given in the Supporting Information. The analysis reveals that the Pauli repulsion between the nitrogen-containing monomer and the catalyst are larger. This contribution is overcompensated by stronger electrostatic and orbital-interaction terms, indicating that the nitrogen-containing functionalities are much better donors than the O ligand.
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