Butadiene cyclooligomerization

The selectivity of butadiene cyclooligomerization in the presence of bis(l,5-cyclooctadiene)-nickel(0) varies with the phosphane added, e.g., monophosphanes, such as (S)-ter/-butyl(iso-propyl)phenylphosphane and (- )-dimethyl(phenyl)phosphane, or diphosphanes, such as Diop. In all cases, 1,5-cyclooctadiene is preferentially formed, along with 4-vinylcyclohexene, ill a 4.5-6 1 ratio. The optical purity of the 4-vinylcyclohexene reaches 12% at a monophosphane/ nickel ratio of about 8 1 and is much lower with Diop57. The use of various 1,3,2-dioxaphospho-lanes with bulky substituents leads to a significant improvement in product selectivity (favoring 4-vinylcyclohexene over 1,5-cyclooctadiene in a ratio of up to 1 0.3) and in the enantioselectiv-ity. The best Optical yield (35% ee, later corrected to 24% ee58) was obtained with a nickel complex of diethyl 2-toT-butyl-l,3,2-dioxaphospholane-4,5-dicarboxylate (1) at 20 C57. 

Scheme 4 Interplay of the alternative reaction channels for production of CiQ-olefins via butadiene/ethylene co-oligomerization and of Ci2-olefins via butadiene cyclooligomerization with zerovalent bare nickel complexes as the catalyst. Gibbs free energies (kcal mol ) are reported relative to the favorable [Ni (ip -syM,ip (C ))A-c s,-octadienediyl)(ethylene)] isomer of 2, while activation barriers are given relative to the respective precursor...

Figure 2.14. A complete mechanism for butadiene cyclooligomerization at all L Ni ratios.

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... 

Comparing [L]-control maps for up to now fifteen different ligands of the nickel-catalyzed cyclooligomerization of butadiene we found eight independent productdetermining l and-association processes (I — VIII). To find out the respective changes in the [L]-control maps, it is extremely helpful to construct product stream diagrams as described in Scheme 3.2-3. 

By contrast, the bisphosphine-anchored catalyst described as [( f—PPh2)2Ni(CO)2] was found to be very similar in activity—both molar turnover rate and product distribution—to its homogeneous counterpart t(PPh3)2Ni(CO)2] in the cyclooligomerization of butadiene (93). Indeed, the only important difference between the supported and the homogeneous catalyst was in the rate the supported catalyst required a temperature of 115°C to achieve the same rate as that of the homogeneous catalyst at 90°C. 

Cyclooligomerization. Ever since the first cyclodimerization reaction of 1,3-butadiene to yield 1,5-cycloctadiene catalyzed by a so-called Reppe catalyst was reported45 [Eq. (13.12)], cyclooligomerization of conjugated dienes has been intensively studied ... 

G. Wilke, Cyclooligomerization of Butadiene and Transition Metal -Complexes, Angew. Chem. Int. Ed. Engl. 2, 105-115 (1963). 

It is appropriate to include here two bis(T)3-allyl)nickel complexes that are formed by reacting zerovalent nickel species with 1,3-dienes and that have been shown to be involved as intermediates in the nickel-catalyzed cyclooligomerization of butadiene, viz., (T)3,i73-C12H18)Ni and (rj3-QH NiPRa. 

Anionic polymerization of ethylene has been used to prepare terminally functionalized ethylene oligomers. The reaction proceeds as shown in equation (12). Phosphite as well as phosphine-hmctionalized ethylene oligomers have been prepared. Nickel(O) phosphine complexes can be bound to such a functionalized oligomer. The bound complexes have similar activity as their homogeneous counterparts for the cyclooligomerization of butadiene. 

Telomerization reactions of dienes are important. While cyclooligomerizations of butadienes with nickel catalysts are technically important for producing the precursors of polyamides or polyesters (cf. Section 2.3.6), the telomerization... 

Thermal cyclooligomerizations of olefins and alkynes require severe and often dangerous reaction conditions and the yields of cyclic products are usually very low. Acetylene ean be trimerized to benzene at 500 °C [1] and butadiene (BD) dimerizes at 270 °C and under high pressure to give small amounts of 1,5-cyclo-octadiene [2]. Reppe s discovery in 1940 that acetylene can be cyclotetramerized to cyclooctatetraene (COT) using a nickel catalyst [3] shows that transition metals can act as templates for the synthesis of cyclic hydrocarbons from acetylenic or olefinic building blocks (Scheme 1). 

The first catalytic cyclodimerization of 1,3-butadiene (BD) to 1,5-cycloocta-diene using modified Reppe catalysts was reported by Reed in 1954 [4], and only two years later Wilke reported on the titanium-catalyzed synthesis of cyclo-dodecatrienes from BD [5]. It remained for Wilke and his co-workers to show the tremendous versatility and scope of the nickel-catalyzed cyclooligomerizations of... 

A remarkable example of the cooperation of different active sites in a polyfunctional catalyst is the one-step synthesis of 2-ethylhexanol, including a combined hydroformylation, aldol condensation, and hydrogenation process [17]. The catalyst in this case is a carbonyl-phosphine-rhodium complex immobilized on to polystyrene carrying amino groups close to the metal center. Another multistep catalytic process is the cyclooligomerization of butadiene combined with a subsequent hydroformylation or hydrogenation step [24, 25] using a styrene polymer on to which a rhodium-phosphine and a nickel-phosphine complex are anchored (cf Section 3.1.5). 

This behaviour correponds to the observation that other unsaturated hydrocarbons, e.g. alkynes, allenes or 1,3-butadienes, which readily undergo transition metal catalyzed cyclooligomerizations, do also incorporate CX multiple bonds in such cycloadditions only with difficulty in most cases 207 208). Besides the well known cobalt-catalyzed pyridin synthesis from alkynes and nitriles98 cocyclooligomerizations have been achieved with alkynes on one side and isocyanates 209), carbodiimides210) and carbondioxide 211) on the other side as well as with 1,3-butadienes and aldehydes 212), carbondioxide213 and 2-aza- or 2,3-diaza- 1,3-butadiene214. ... 

Table 1. Products from the Ni-Ligand Catalyzed Cyclooligomerization OF Butadiene " ...

Enantioselective cyclooligomerizations of butadiene can also be achieved when a chiral diaza-diene-iron(II) chloride complex and a fourfold excess of ethylmagnesium iodide are used. Optical yields of 9 to 16% are obtained with two chiral diazadienes of the type R N = CRCR = NR, prepared by formic acid catalyzed condensation of aqueous glyoxal (R1 = H) or 2,3-butadione (R1 = CH3) with (R)-l-phenylethylaminc or (1S,2S,3S,5R)-3-(aminomethyl)pinane. The (di-azadienc)iron(0)-catalyzed dimerization of butadiene also gives 4-vinylcyclohexene with up to 16% ee60. 

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