The role of bulky substituents in Brookhart-type Ni(II) diimine catalyzed olefin polymerization: A combined density functional theory and molecular mechanics study

被引:338
作者
Deng, LQ
Woo, TK
Cavallo, L
Margl, PM
Ziegler, T
机构
[1] UNIV CALGARY,DEPT CHEM,CALGARY,AB T2N 1N4,CANADA
[2] UNIV NAPLES FEDERICO II,DIPARTMENTO CHIM,I-80134 NAPLES,ITALY
关键词
D O I
10.1021/ja970226a
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
The role of the bulky ligands in Ni(II) diimine catalyzed ethylene polymerization has been examined with a combined density functional theory quantum mechanics and molecular mechanics (QM/MM) model. Specifically, we have examined the catalytic center of the type (ArN=C(R)-C(R)=NAr)Ni-II-R'(+), where R = Me and Ar = 2,6-C6H3(i-Pr)(2). The Ar and R groups were treated by a molecular mechanics force field while density functional theory was applied to the remainder of the system. The chain propagation, chain branching, and chain termination processes have been investigated with the hybrid method and found to have barriers of Delta H-double dagger = 11.8, 15.3, and 18.4 kcal/mol, respectively, which is in excellent agreement with experiment in both absolute and relative terms. This is in stark contrast to the pure QM model in which the influence of the bulky Ar and R groups was neglected and the established order of the barriers is not even reproduced. The role played by the bulky substituents is dual in nature. First, the Ar and R groups act to sterically hinder the axial coordination sites of the Ni center. This has the most dramatic destabilizing effect on the resting state and termination transition states, in which both axial positions are occupied. In addition to the steric factor, we find that the electronic preference for the aryl rings to orient themselves in a coplanar fashion with the diimine ring results in a stabilization of the insertion transition state relative to the resting state. These two factors act to both lower the propagation barrier and increase the termination barrier compared to the ''naked'' pure QM model system.
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收藏
页码:6177 / 6186
页数:10
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  • [1] ABECYWICKREMA R, 1993, J CHEM SOC DA, P59
  • [2] [Anonymous], [No title captured], DOI DOI 10.1016/0021-9991(92)90277-6
  • [3] Self-consistent molecular Hartree-Fock-Slater calculations - I. The computational procedure
    Baerends, E. J.
    Ellis, D. E.
    Ros, P.
    [J]. CHEMICAL PHYSICS, 1973, 2 (01) : 41 - 51
  • [4] Self-consistent molecular Hartree-Fock-Slater calculations - II. The effect of exchange scaling in some small molecules
    Baerends, E. J.
    Ros, P.
    [J]. CHEMICAL PHYSICS, 1973, 2 (01) : 52 - 59
  • [5] DENSITY-FUNCTIONAL EXCHANGE-ENERGY APPROXIMATION WITH CORRECT ASYMPTOTIC-BEHAVIOR
    BECKE, AD
    [J]. PHYSICAL REVIEW A, 1988, 38 (06): : 3098 - 3100
  • [6] STEREOSPECIFIC OLEFIN POLYMERIZATION WITH CHIRAL METALLOCENE CATALYSTS
    BRINTZINGER, HH
    FISCHER, D
    MULHAUPT, R
    RIEGER, B
    WAYMOUTH, RM
    [J]. ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 1995, 34 (11) : 1143 - 1170
  • [7] THE OLIGOMERIZATION OF ETHENE WITH CATALYSTS EXHIBITING ENZYME-LIKE ACTIVITIES
    BROWN, SJ
    MASTERS, AF
    [J]. JOURNAL OF ORGANOMETALLIC CHEMISTRY, 1989, 367 (03) : 371 - 374
  • [8] ZIEGLER-NATTA CATALYSIS - A THEORETICAL-STUDY OF THE ISOTACTIC POLYMERIZATION OF PROPYLENE
    CASTONGUAY, LA
    RAPPE, AK
    [J]. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1992, 114 (14) : 5832 - 5842
  • [9] A density functional and molecular mechanics study of beta-hydrogen transfer in homogeneous Ziegler-Natta catalysis
    Cavallo, L
    Guerra, G
    [J]. MACROMOLECULES, 1996, 29 (08) : 2729 - 2737
  • [10] A 2ND GENERATION FORCE-FIELD FOR THE SIMULATION OF PROTEINS, NUCLEIC-ACIDS, AND ORGANIC-MOLECULES
    CORNELL, WD
    CIEPLAK, P
    BAYLY, CI
    GOULD, IR
    MERZ, KM
    FERGUSON, DM
    SPELLMEYER, DC
    FOX, T
    CALDWELL, JW
    KOLLMAN, PA
    [J]. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1995, 117 (19) : 5179 - 5197