PowerPoint-Pr

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Martin-Luther-University of Halle-Wittenberg Unive
rsity of Calgary
Ni0L-catalyzed cyclodimerization of
butadiene A computational study based on the
generic Ni0(butadiene)2PH3 catalyst.
Sven Tobisch and Tom Ziegler
ICCC35 Heidelberg, Germany, July 23, 2002
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Ni0L-catalyzed cyclodimerization of butadiene

• General Introduction
• first observation by Reed (H.B.W Reed J.
  Chem. Soc. 1954, 1931.)
• systematic exploration by Wilke et al.
• multistep addition-elimination mechanism (Ni0 ?
  NiII)
• active catalyst complex ? bis(butadiene)Ni0L (L
  PR3, P(OR)3)
• products of the catalytic cyclodimerization

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Catalytic cycle of the Ni0L-catalyzed
cyclodimerization of 1,3-butadiene (in essential
parts according to Wilke et al. ? G. Wilke et
al. J. Organomet. Chem. 1985, 279, 63.)
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Ni0L-catalyzed cyclodimerization of butadiene

• Computational Details
• DFT-calculations with a gradient-corrected
  XC-functional (BP86)
• A. D. Becke Phys. Rev. 1988, A38, 3098.
• J. P. Perdew Phys. Rev. 1986, B33, 8822 Phys.
  Rev. 1986, B34, 7406.
• All-electron basis set of triple-? quality for
  the valence electrons augmented with polarization
  functions

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Stereoisomers of the active catalyst and of
octadienediyl-NiII species
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Ni0L-catalyzed cyclodimerization of butadiene

• mechanistic details that are not yet firmly
  established
• What is the geometric structure of the
  Ni0(butadiene)2L active catalyst and how does
  oxidative coupling of two butadiene moieties
  occur?
• What type of octadienediylNiII species are
  involved in the reductive elimination steps?
• What role plays allylic isomerization in the
  course of the catalytic process?
• Which elementary process is rate-determining?

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A - oxidative coupling of two butadiene moieties
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A - oxidative coupling of two butadiene moieties
Key structures involved along the most feasible
pathway via 1 ? 2 (?2-cis/trans-BD coupling
(opposite enantiofaces))
TS1-2
NiII(h3,h1(C1)-C8H12)L 2
Ni0(h2-BD)2L 1
?G 13.6 kcal mol-1 ?G 0.1 kcal mol-1
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B thermodynamic stability of different forms
of the NiII(C8H12)L complex
?G kcal mol-1 2 3 4 5 6 7
1.5 5.0 0.0 30.7 28.1 29.3
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C allylic isomerization in octadienediylNiII
species
isomerization of an h3-allylic group via an s-C3
intermediate

• J. W. Faller et al. J. Am. Chem. Soc. 1971, 93,
  2642.
• S. Tobisch, R. Taube Organometallics 1999, 18,
  3045.

TSISO3
?G 13.2 kcal mol-1
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D reductive elimination under ring closure
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D reductive elimination under ring closure
Key structures involved along the most feasible
pathways
VCH route
?G 25.3 kcal mol-1 ?G -10.2 kcal mol-1
TS2-8
h4-VCH-Ni0 8
h3,h1(C1)-NiII 2
cis-1,2-DVCB route
?G 22.7 kcal mol-1 ?G 3.2 kcal mol-1
TS4-9
h4-DVCB-Ni0 9
cis,cis-COD route
bis(h3)-NiII 4
?G 22.5 kcal mol-1 ?G -0.2 kcal mol-1
TS4-10
h4-COD-Ni0 10
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Ni0L-catalyzed cyclodimerization of butadiene

• Conclusions

• The Ni0(h2-BD)2L complex 1 is the active
  catalyst complex.
• Oxidative coupling most likely proceeds via
  coupling of the terminal non-coordinating carbons
  of two ?2-BD moieties.
• NiII(?3,?1(C1)-C8H12)L species are formed as
  initial coupling product. All octadienediyl NiII
  species are in a pre-established equi-librium,
  due to facile allylic isomerization. 2 and 4 are
  the prevailing octadienediylNiII species.
• Bis(?1)-octadienediylNiII species play no role
  in the reaction course.
• The reductive elimination is rate-determi-ning
  and proceeds via direct paths.
• cis,cis-COD is predicted to be the predomi-nant
  product for the generic Ni0(?2-butadiene)2PH3
  catalyst.

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Ni0L-catalyzed cyclodimerization of butadiene

• published work
• Ni0L-Catalyzed Cyclodimerization of
  1,3-Butadiene A Comprehensive Density Functional
  Investigation Based on the Generic
  (C4H6)2Ni0PH3 Catalyst.
• S. Tobisch, T. Ziegler J. Am. Chem. Soc. 2002,
  124, 4881.
• Ni0L-Catalyzed Cyclodimerization of
  1,3-Butadiene A Density Functional Investigation
  of the Influence of Electronic and Steric Factors
  on the Regulation of the Selectivity.
• S. Tobisch, T. Ziegler J. Am. Chem. Soc.,
  accepted for publication

• Acknowledgement
• Prof. T. Ziegler (University of Calgary) and
  members of his goup
• Deutsche Forschungsgemeinschaft (DFG)