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[Ni[Ni00L]-catalyzed cyclodimerization of butadiene:L]-catalyzed cyclodimerization of butadiene:A computational study based on the generic A computational study based on the generic

[Ni[Ni00(butadiene)(butadiene)22PHPH33] catalyst.] catalyst.

Sven TobischSven Tobisch and Tom Ziegler and Tom Ziegler

Martin-Luther-University of Halle-Wittenberg

University of Calgary

ICCC35 Heidelberg, Germany, July 23, 2002

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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

[Ni[Ni00L]-catalyzed cyclodimerization of butadieneL]-catalyzed cyclodimerization of butadiene

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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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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

[Ni[Ni00L]-catalyzed cyclodimerization of butadieneL]-catalyzed cyclodimerization of butadiene

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Stereoisomers of the active catalyst and of octadienediyl-NiII species

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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 octadienediyl—NiII 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?

[Ni[Ni00L]-catalyzed cyclodimerization of butadieneL]-catalyzed cyclodimerization of butadiene

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A - oxidative coupling of two butadiene moietiesA - oxidative coupling of two butadiene moieties

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A - oxidative coupling of two butadiene moietiesA - oxidative coupling of two butadiene moieties

Key structures involved along the most feasible pathway via 1 2(2-cis/trans-BD coupling (opposite enantiofaces))

[Ni0(2-BD)2L]

1TS[1-2] [NiII(3,1(C1)-C8H12)L]

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G‡ = 13.6 kcal mol-1

G = 0.1 kcal mol-1

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B – thermodynamic stability of different forms B – thermodynamic stability of different forms of the [Niof the [NiIIII(C(C88HH1212)L] complex)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 octadienediyl—NiC – allylic isomerization in octadienediyl—NiIIII species species

isomerization of an 3-allylic group via an -C3 intermediate

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

TSISO[3]

G‡ = 13.2 kcal mol-1

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D – reductive elimination under ring closureD – reductive elimination under ring closure

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D – reductive elimination under ring closureD – reductive elimination under ring closure

3,1(C1)-NiII 2 TS[2-8] 4-VCH-Ni0 8

Key structures involved along the most feasible pathways

VCH route

G‡ = 25.3 kcal mol-1

G = -10.2 kcal mol-1

bis(3)-NiII 4

TS[4-9] 4-DVCB-Ni0 9

cis-1,2-DVCB route

G‡ = 22.7 kcal mol-1

G = 3.2 kcal mol-1

cis,cis-COD route

G‡ = 22.5 kcal mol-1

G = -0.2 kcal mol-1

TS[4-10] 4-COD-Ni0 10

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[Ni[Ni00L]-catalyzed cyclodimerization of butadieneL]-catalyzed cyclodimerization of butadiene

Conclusions• The [Ni0(2-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 octadienediyl—NiII species.

• Bis(1)-octadienediyl—NiII 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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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

[Ni[Ni00L]-catalyzed cyclodimerization of butadieneL]-catalyzed cyclodimerization of butadiene

Acknowledgement:

• Prof. T. Ziegler (University of Calgary) and members of his goup

• Deutsche Forschungsgemeinschaft (DFG)