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[Ni 0 L]-catalyzed cyclodimerization of butadiene: A computational study based on the generic [Ni 0 (butadiene) 2 PH 3 ]

Martin-Luther-University of Halle-Wittenberg University of Calgary. [Ni 0 L]-catalyzed cyclodimerization of butadiene: A computational study based on the generic [Ni 0 (butadiene) 2 PH 3 ] catalyst. Sven Tobisch and Tom Ziegler. ICCC35 Heidelberg, Germany, July 23, 2002.

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[Ni 0 L]-catalyzed cyclodimerization of butadiene: A computational study based on the generic [Ni 0 (butadiene) 2 PH 3 ]

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  1. Martin-Luther-University of Halle-Wittenberg University 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

  2. [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

  3. 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.)

  4. [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

  5. Stereoisomers of the active catalyst and of octadienediyl-NiII species

  6. [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 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?

  7. A - oxidative coupling of two butadiene moieties

  8. 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)) TS[1-2] [NiII(h3,h1(C1)-C8H12)L] 2 [Ni0(h2-BD)2L] 1 G‡ = 13.6 kcal mol-1 G = 0.1 kcal mol-1

  9. B – thermodynamic stability of different forms of the [NiII(C8H12)L] complex

  10. C – allylic isomerization in octadienediyl—NiII 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 Organometallics1999, 18, 3045. TSISO[3] G‡ = 13.2 kcal mol-1

  11. D – reductive elimination under ring closure

  12. D – reductive elimination under ring closure Key structures involved along the most feasible pathways VCH route G‡ = 25.3kcal mol-1 G = -10.2kcal mol-1 TS[2-8] h4-VCH-Ni08 h3,h1(C1)-NiII2 cis-1,2-DVCB route G‡ = 22.7kcal mol-1 G = 3.2kcal mol-1 TS[4-9] h4-DVCB-Ni09 cis,cis-COD route bis(h3)-NiII4 G‡ = 22.5kcal mol-1 G = -0.2kcal mol-1 TS[4-10] h4-COD-Ni010

  13. [Ni0L]-catalyzed cyclodimerization of butadiene • 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 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. Conclusions

  14. [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)

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