Butadiene, catalyzed reactions oligomerization

Although the pioneering, systematic, and comprehensive experimental work of Wilke et al3,5 has led to a thorough understanding of the nickel-catalyzed cyclo-oligomerization reaction of 1,3-butadiene, there are still some essential mechanistic details that are not yet firmly established (vide infra). In the following account, we summarize recent progress in the... 

CATALYTIC REACTION CYCLES FOR THE NICKEL-CATALYZED CYCLO-OLIGOMERIZATION OF 1,3-BUTADIENE... 

Scheme 4. Condensed free-energy profile (kcalmol-1) of the complete catalytic cycle of the C8-reaction channel of the nickel-catalyzed cyclo-oligomerization of 1,3-butadiene for catalyst IV with L = P(OPh)3. The favorable [Ni°(p2-tr

In this account we have presented a consistent and theoretically well-founded view of the catalytic structure-reactivity relationships for the nickel-catalyzed cyclo-oligomerization of 1,3-butadiene, which represents one of the key reactions in homogeneous catalysis that, furthermore, has... 

Solutions of the nickel(O) and palladium(O) complexes of 1,3,5-triaza-7-phosphaadamantane, PTA (82) and tris(hydroxymethyl)phosphine (98) in water catalyze the oligomerization and telomerization of 1,3-butadiene at 80 °C. Although high yields and good selectivities to octadienyl products (87 %) were obtained, the complexes (or the intermediate species formed in the reaction) dissolve sufficiently in the organic phase ofthe monomer and the products to cause substantial metal leaching [17],... 

When some other reaction parameter, Z, such as the log of a rate constant, is plotted on to this steric and electronic map on an axis normal to the plane of the paper the comparative contributions of 6 and v should become apparent. A purely steric effect will slope north or south (the reader is encouraged to view Figures 26-28 of ref. 187 to appreciate this fully). Weimann and co-workers211 used Tolman s methodology to show the % steric effect in the oligomerization of butadiene catalyzed by nickel phosphine complexes. 

This chapter is organized as follows. In the following section the tentative catalytic cycle proposed by Wilke and co-workers is outlined, followed, in the next section, by a short description of the computational approach employed and the catalyst model chosen. The structural and energetic aspects of all critical elementary steps of the complete catalytic cycle are presented after that. Then we propose a theoretically verified, refined catalytic reaction cycle, and follow that with the elucidation of the product distribution between linear and cyclic Cjo-olefins. Finally, the catalytic reaction courses of the [Ni°]-catalyzed co-oligomerization of 1,3-butadiene and ethylene and of the cyclooligomerization of 1,3-butadiene are compared. 

The catalytic cyclo-oligomerization of 1,3-butadiene mediated by transition-metal complexes is one of the key reactions in homogeneous catalysis.1 Several transition metal complexes and Ziegler-Natta catalyst systems have been established that actively catalyze the stereoselective cyclooligomerization of 1,3-dienes.2 Nickel complexes, in particular, have been demonstrated to be the most versatile catalysts.3... 

The catalytic cyclo-oligomerization of 1,3-butadiene was first reported by Reed in 1954 using modified Reppe catalysts.4 Wilke et al., however, demonstrated in pioneering, comprehensive and systematic mechanistic investigations, the implications, versatility and the scope of the nickel-catalyzed 1,3-diene cyclo-oligomerization reactions.3,5... 

It should be noted here again that the catalytic reaction does not involve a change of valence of the metal. In general, catalytic olefin addition reactions that involve a hydride transfer do not require change of valence in the metal catalyst. On the other hand, carbon-carbon bond formation by coupling reactions which involve electron shifts, such as in Wilke s Ni°-catalyzed butadiene oligomerization reaction [Eq. (1)], requires a valence change on the metal. 

As discussed in connection with olefin-coupling reactions and shown in Fig. 4, the coupling of vinyl Grignard reagents is stereospecific and dependent upon the transition metal catalyst used (32, 33). The dimerization of ethylene, shown in Fig. 6, was also shown to produce primarily the terminal olefin 1-butene (35). The size of the metal has also been shown to influence the course of the catalyzed oligomerization reactions of butadiene. When bis-(ir-allyl) metal complexes are used as... 

Heterogcnized complexes have been used to catalyze a great number of reactions, such as hydrogenation [18], hydroformylation [19], ethylene oligomerization [20], hydrosilylation [21, 22], polymerization [23], telo-merization [24], oxidation [25], oligomerization of monoalkenc [26], methanol carbonylation [27], butadiene oligomerization [28], synthesis gas chemistry [29], and isomerization [30],... 

Butadiene as raw material is available in high amounts from the C4 fraction of raffmation processes. The telomerization of butadiene itself catalyzed by different metal catalysts is a well documented reaction. Depending on the catalyst and on the conditions different telomeres may be synthesized. Carrying out the reaction under carbon dioxide instead of argon atmosphere, 1,3,7-octatriene becomes the main product Pioneering work of Inoue and co-workers in 1976 showed that the same reaction under carbon dioxide atmosphere lead to co-oligomeres 2, 5 and 6 when palladium complexes are used as catalysts (Scheme 1). 

So far we have proposed a refined catalytic reaction cycle for the co-oUgomer-ization process and have furthermore analyzed the catalytic structure-reactivity relationships for the regulation of the Cm-olefin product selectivity. This, together with our recent theoretical-mechanistic exploration of the [Ni ]-catalyzed 1,3-butadiene cyclooUgomerization affording Cij-cycloolefins [4c,d], enables us now to undertake a comparison of crucial mechanistic aspects of the two reactions. Furthermore, the interplay of the two alternative reaction channels for co-oligomerization and cyclooligomerization wiU be analyzed (Scheme 4). 

Simple 1,3-dienes such as 1,3-butadiene, isoprene, and related compounds undergo efficient metal-catalyzed oligomerization. Under palladium catalysis, diene dimerization is the most common oligomerization reaction observed. Four modes of dimerization have been reported (Scheme 1) (i) [2 + 2] cycloaddition to afford 1,2-divinylcyclobutane (1) (ii) [4 -I- 2] cycloaddition to afford 4-vinylcyclohexene (2) (iii) [4 + 4] cycloaddition to afford 1,4-cyclooctadiene (3) and (iv) linear dimerization to afford 1,3,7-octatriene (4). 

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