Zirconocene ketimides: Synthesis, structural characterization, ethylene polymerization activity, and ab initio computational studies

D.R. Armstrong, K.W. Henderson, I. Little, C. Jenny, A.R. Kennedy, A.E. McKeown, R.E. Mulvey

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

The metathetical reaction between the lithium 1-azaallyl compound [{HMPA·LiN(H)C(t-Bu)CH2}2] (1) with zirconocene dichloride (2) results in the formation of the zirconocene ketimide [Cp2Zr(Cl)N=C(t-Bu)CH3] (3; Cp = cyclopentadienyl) and lithium chloride. After it is transferred to the transition metal, the azaallyl ligand isomerizes to a ketimido variation. An energetic preference of 11.9 kcal mol-1 in favor of the zirconocene ketimide over its theoretical azaallyl isomer was determined by ab initio molecular orbital calculations (at the HF/LanL2DZ level). These studies, in combination with an X-ray diffraction analysis of 3, suggest that the preference for the ketimide isomer is due to the presence of a heteroallenic (Zr-N-C) interaction. This bonding mode is consistent with the short Zr-N bond length of 2.007(2) î.. found in the crystal structure of 3. Treatment of 3 with MeLi affords the corresponding methyl derivative [Cp2Zr(Me)N=C(t-Bu)CH3] (4). 1H NMR spectroscopic experiments reveal that addition of the Lewis acid B(C6F5)3 to 4 results in methide abstraction, with retention of the ketimide unit on the cationic zirconocene. Ab initio molecular orbital calculations confirmed the energetic preference for the 1-ketimide cation [Cp2ZrN=C(t-Bu)CH3]+ over either the 1-azaallyl isomer [Cp2Zr{1-N(H)C(t-Bu)CH2}]+ or the 3-azaallyl isomer [Cp2Zr{3-N(H)C(t-Bu)CH2}]+ (by 17.9 and 1.2 kcal mol-1, respectively). Both 3 and 4 have been shown to be active catalysts for the polymerization of ethylene in combination with a MAO cocatalyst. In addition, 4 polymerizes ethylene in combination with a mixed B(C6F5)3/i-Bu3Al cocatalyst.
LanguageEnglish
Pages4369-4375
Number of pages6
JournalOrganometallics
Volume19
Issue number21
DOIs
Publication statusPublished - 20 Sep 2000

Fingerprint

Isomers
ethylene
Thermodynamic properties
isomers
polymerization
Polymerization
Orbital calculations
Molecular orbitals
synthesis
molecular orbitals
Hempa
Lithium Chloride
lithium chlorides
Lewis Acids
dichlorides
Monoamine Oxidase
Bond length
Lithium
X ray diffraction analysis
Transition metals

Keywords

  • metathetical reaction
  • zirconocene dichloride
  • lithium chloride
  • ketimide
  • crystal structure
  • ethylene

Cite this

Armstrong, D.R. ; Henderson, K.W. ; Little, I. ; Jenny, C. ; Kennedy, A.R. ; McKeown, A.E. ; Mulvey, R.E. / Zirconocene ketimides: Synthesis, structural characterization, ethylene polymerization activity, and ab initio computational studies. In: Organometallics. 2000 ; Vol. 19, No. 21. pp. 4369-4375.
@article{3343b665819c44dc8b2123f514e6afab,
title = "Zirconocene ketimides: Synthesis, structural characterization, ethylene polymerization activity, and ab initio computational studies",
abstract = "The metathetical reaction between the lithium 1-azaallyl compound [{HMPA·LiN(H)C(t-Bu)CH2}2] (1) with zirconocene dichloride (2) results in the formation of the zirconocene ketimide [Cp2Zr(Cl)N=C(t-Bu)CH3] (3; Cp = cyclopentadienyl) and lithium chloride. After it is transferred to the transition metal, the azaallyl ligand isomerizes to a ketimido variation. An energetic preference of 11.9 kcal mol-1 in favor of the zirconocene ketimide over its theoretical azaallyl isomer was determined by ab initio molecular orbital calculations (at the HF/LanL2DZ level). These studies, in combination with an X-ray diffraction analysis of 3, suggest that the preference for the ketimide isomer is due to the presence of a heteroallenic (Zr-N-C) interaction. This bonding mode is consistent with the short Zr-N bond length of 2.007(2) {\^i}.. found in the crystal structure of 3. Treatment of 3 with MeLi affords the corresponding methyl derivative [Cp2Zr(Me)N=C(t-Bu)CH3] (4). 1H NMR spectroscopic experiments reveal that addition of the Lewis acid B(C6F5)3 to 4 results in methide abstraction, with retention of the ketimide unit on the cationic zirconocene. Ab initio molecular orbital calculations confirmed the energetic preference for the 1-ketimide cation [Cp2ZrN=C(t-Bu)CH3]+ over either the 1-azaallyl isomer [Cp2Zr{1-N(H)C(t-Bu)CH2}]+ or the 3-azaallyl isomer [Cp2Zr{3-N(H)C(t-Bu)CH2}]+ (by 17.9 and 1.2 kcal mol-1, respectively). Both 3 and 4 have been shown to be active catalysts for the polymerization of ethylene in combination with a MAO cocatalyst. In addition, 4 polymerizes ethylene in combination with a mixed B(C6F5)3/i-Bu3Al cocatalyst.",
keywords = "metathetical reaction, zirconocene dichloride, lithium chloride, ketimide, crystal structure, ethylene",
author = "D.R. Armstrong and K.W. Henderson and I. Little and C. Jenny and A.R. Kennedy and A.E. McKeown and R.E. Mulvey",
year = "2000",
month = "9",
day = "20",
doi = "10.1021/om000451s",
language = "English",
volume = "19",
pages = "4369--4375",
journal = "Organometallics",
issn = "0276-7333",
publisher = "American Chemical Society",
number = "21",

}

Zirconocene ketimides: Synthesis, structural characterization, ethylene polymerization activity, and ab initio computational studies. / Armstrong, D.R.; Henderson, K.W.; Little, I.; Jenny, C.; Kennedy, A.R.; McKeown, A.E.; Mulvey, R.E.

In: Organometallics, Vol. 19, No. 21, 20.09.2000, p. 4369-4375.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Zirconocene ketimides: Synthesis, structural characterization, ethylene polymerization activity, and ab initio computational studies

AU - Armstrong, D.R.

AU - Henderson, K.W.

AU - Little, I.

AU - Jenny, C.

AU - Kennedy, A.R.

AU - McKeown, A.E.

AU - Mulvey, R.E.

PY - 2000/9/20

Y1 - 2000/9/20

N2 - The metathetical reaction between the lithium 1-azaallyl compound [{HMPA·LiN(H)C(t-Bu)CH2}2] (1) with zirconocene dichloride (2) results in the formation of the zirconocene ketimide [Cp2Zr(Cl)N=C(t-Bu)CH3] (3; Cp = cyclopentadienyl) and lithium chloride. After it is transferred to the transition metal, the azaallyl ligand isomerizes to a ketimido variation. An energetic preference of 11.9 kcal mol-1 in favor of the zirconocene ketimide over its theoretical azaallyl isomer was determined by ab initio molecular orbital calculations (at the HF/LanL2DZ level). These studies, in combination with an X-ray diffraction analysis of 3, suggest that the preference for the ketimide isomer is due to the presence of a heteroallenic (Zr-N-C) interaction. This bonding mode is consistent with the short Zr-N bond length of 2.007(2) î.. found in the crystal structure of 3. Treatment of 3 with MeLi affords the corresponding methyl derivative [Cp2Zr(Me)N=C(t-Bu)CH3] (4). 1H NMR spectroscopic experiments reveal that addition of the Lewis acid B(C6F5)3 to 4 results in methide abstraction, with retention of the ketimide unit on the cationic zirconocene. Ab initio molecular orbital calculations confirmed the energetic preference for the 1-ketimide cation [Cp2ZrN=C(t-Bu)CH3]+ over either the 1-azaallyl isomer [Cp2Zr{1-N(H)C(t-Bu)CH2}]+ or the 3-azaallyl isomer [Cp2Zr{3-N(H)C(t-Bu)CH2}]+ (by 17.9 and 1.2 kcal mol-1, respectively). Both 3 and 4 have been shown to be active catalysts for the polymerization of ethylene in combination with a MAO cocatalyst. In addition, 4 polymerizes ethylene in combination with a mixed B(C6F5)3/i-Bu3Al cocatalyst.

AB - The metathetical reaction between the lithium 1-azaallyl compound [{HMPA·LiN(H)C(t-Bu)CH2}2] (1) with zirconocene dichloride (2) results in the formation of the zirconocene ketimide [Cp2Zr(Cl)N=C(t-Bu)CH3] (3; Cp = cyclopentadienyl) and lithium chloride. After it is transferred to the transition metal, the azaallyl ligand isomerizes to a ketimido variation. An energetic preference of 11.9 kcal mol-1 in favor of the zirconocene ketimide over its theoretical azaallyl isomer was determined by ab initio molecular orbital calculations (at the HF/LanL2DZ level). These studies, in combination with an X-ray diffraction analysis of 3, suggest that the preference for the ketimide isomer is due to the presence of a heteroallenic (Zr-N-C) interaction. This bonding mode is consistent with the short Zr-N bond length of 2.007(2) î.. found in the crystal structure of 3. Treatment of 3 with MeLi affords the corresponding methyl derivative [Cp2Zr(Me)N=C(t-Bu)CH3] (4). 1H NMR spectroscopic experiments reveal that addition of the Lewis acid B(C6F5)3 to 4 results in methide abstraction, with retention of the ketimide unit on the cationic zirconocene. Ab initio molecular orbital calculations confirmed the energetic preference for the 1-ketimide cation [Cp2ZrN=C(t-Bu)CH3]+ over either the 1-azaallyl isomer [Cp2Zr{1-N(H)C(t-Bu)CH2}]+ or the 3-azaallyl isomer [Cp2Zr{3-N(H)C(t-Bu)CH2}]+ (by 17.9 and 1.2 kcal mol-1, respectively). Both 3 and 4 have been shown to be active catalysts for the polymerization of ethylene in combination with a MAO cocatalyst. In addition, 4 polymerizes ethylene in combination with a mixed B(C6F5)3/i-Bu3Al cocatalyst.

KW - metathetical reaction

KW - zirconocene dichloride

KW - lithium chloride

KW - ketimide

KW - crystal structure

KW - ethylene

UR - http://dx.doi.org/10.1021/om000451s

U2 - 10.1021/om000451s

DO - 10.1021/om000451s

M3 - Article

VL - 19

SP - 4369

EP - 4375

JO - Organometallics

T2 - Organometallics

JF - Organometallics

SN - 0276-7333

IS - 21

ER -