Nickel complexes diene dimerization

Another example is butene dimerization catalyzed by nickel complexes in acidic chloroaluminates 14). This reaction has been performed on a continuous basis on the pilot scale by IFF (Difasol process). Relative to the industrial process involving homogeneous catalysis (Dimersol process), the overall yield in dimers is increased. Similarly, selective hydrogenation of diene can be performed in ionic liquids, because the solubility of dienes is higher than that of monoene, which is higher than that of paraffins. In the case of the Difasol process, a reduction of the volume of the reaction section by a factor of up to 40 can be achieved. This new Difasol technology enables lower dimer (e.g., octenes) production costs 14). 

Homogeneous nickel complexes proved to be versatile catalysts in dimerization and trimerization of dienes to yield different oligomeric products.46-55 Depending on the actual catalyst structure, nickel catalyzes the dimerization of 1,3-butadiene to yield isomeric octatrienes, and the cyclodimerization and cyclotrimerization to give 1,5-cyclooctadiene and all-trans-l,5,9-cyclododecatriene, respectively46 56 [Eq. (13.13)]. Ziegler-type complexes may be used to form cis,trans,trans-1,5,9-cyclododecatriene37,57 58 [Eq. (13.14)], which is an industrial intermediate ... 

The most widely used application of nickel-diene complexes is the dimerization of 1,3-dienes. Pioneering studies hy WiUce demonstrated many different modes of coupling, including dimerization, trimerization, and oligomerization of 1,3-dienes.l An overview of the product classes that maybe obtained from 1,3-dienes is provided in Scheme 4 (see also Houben-Weyl, Vol. E18, pp 93 and 932-937). The initially formed nickel complexes 5 and 6 have not been isolated. However, the complexes may be stabilized by the addition of phosphines, and jr-allyl complexes 7-9 have been prepared and characterized. 

Nickel(O) complexes are extremely effective for the dimerization and oligomerization of conjugated dienes [8,9]. Two molecules of 1,3-butadiene readily undergo oxidative cyclization with a Ni(0) metal to form bis-allylnickel species. Palladium(O) complexes also form bis-allylpalladium species of structural similarity (Scheme 2). The bis-allylpalladium complexes show amphiphilic reactivity and serve as an allyl cation equivalent in the presence of appropriate nucleophiles, and also serve as an allyl anion equivalent in the presence of appropriate electrophiles. Characteristically, the bis-allylnickel species is known to date only as a nucleophile toward carbonyl compounds (Eq. 1) [10,11],... 

Table II also lists several isomerizations and skeletal rearrangements (examples 4-7) which are related to butadiene-ethylene dimerization. Protonation of phosphorus-containing nickel(O) complexes is sufficient to achieve skeletal rearrangement of 1,4-dienes in a few seconds at room temperature, probably via cyclopropane intermediates (example 6, Table II). For small ring rearrangements see Bishop (69).

The linear telomerization reaction of dienes was one of the very first processes catalyzed by water soluble phosphine complexes in aqueous media [7,8]. The reaction itself is the dimerization of a diene coupled with a simultaneous nucleophilic addition of HX (water, alcohols, amines, carboxylic acids, active methylene compounds, etc.) (Scheme 7.3). It is catalyzed by nickel- and palladium complexes of which palladium catalysts are substantially more active. In organic solutions [Pd(OAc)2] + PPhs gives the simplest catalyst combination and Ni/IPPTS and Pd/TPPTS were suggested for mnning the telomerizations in aqueous/organic biphasic systems [7]. An aqueous solvent would seem a straightforward choice for telomerization of dienes with water (the so-called hydrodimerization). In fact, the possibility of separation of the products and the catalyst without a need for distillation is a more important reason in this case, too. 

When (2,2 -bipyridine)(cycloocta-l,5-diene)nickel was used as the catalyst various isomeric (2,2 -bipyridyl)nickelaspirocycloalkanes 4 and 5a-c were isolated.As expected, treatment of the dispiro complex 4 with methyl acrylate or maleic anhydride released dispiro[2.1.2.1]oc-tane (1) whereas the complexes 5 with one cyclopropane ring opened gave mainly 5-methyl-enespiroheptane 2. The formation of the 4-methylene isomer (from 5c) has not been observed in the dimerization reaction with other nickel(O) complexes. A few more nickel(O) complexes with an ability to catalyze the oligomerization of methylenecyclopropane have been de-scribed. ... 

The reactions of metal complexes of monoterpenes continue to be actively explored and many specific examples will be found in later sections. Of general interest are the dimerization of 7r-allyl-Pd complexes of a- and p-pinenes and of carvone that are effected by irradiation at 366 nmM and the thermal decompositions of (TC-allyl)nickel halide complexes of, e.g., isoprene (33), to form myrcene.95 Hydrosilylation of 1,3-dienes e.g. isoprene, myrcene, ocimene) was found to be a regiospecific 1,4-addition for Pd complexes but followed the alternative route for Rh compounds a good discussion is appended.96 A series of dimers of isoprene... 

Perhaps the most useful of the r 3 allyl complexes (cf. 24) are the Jt-allyls of nickel.15 The simplest type 61 are rather unstable and form the bromide-bridged complex 62 on treatment with HBr. These are stable compounds officially complexes of Ni(I) but better regarded for our purpose as dimers of r 3 complexes of allyl anions and Ni(II), much as allyl Grignard reagents 2 can be regarded as o-complexes of allyl anions and Mg(II). Direct exchange of Mg(II) for Ni(II) gives the unstable complexes 61, but the stable dimer 62 can be made by oxidative insertion of Ni(0), as its cyclo-octa-1,5-diene (COD) complex, into allyl bromide 1. 

Reagents. The lithium metal, containing a maximum of 0.05% sodium, was obtained from the Lithium Corporation of America. Bis(l,5-cycloocta-diene)nickel [(Cod)2Ni)] was prepared by a modification of a known procedure (13). This complex was used to prepare tetrakis(triethylphosphine)nickel [(Et3P)4Ni]. Tetraphenylcyclobutadienenickel(II) bromide dimer was synthesized from stilbene-free diphenylacetylene (14). 

A variety of nickel(O) complexes, when treated tvith allyhc electrophiles, afford jt-allyl complexes (see also Houben-Weyl, Vol. E18, pp 64 and 76).l In early studies, tetracarbon-ylnickel(O) was widely employed. However, otving to its extreme toxicity, it is now rarely used. Direct treatment of bis(T] -cycloocta-l,5-diene)nickel(0) (2) with allyl halides such as 20 is now the method of choice for the stoichiometric preparation of nickel-3t-allyl complexes. In the absence of strong donor ligands such as phosphines, halo-bridged dimers (e.g., 21) are t5T3ically obtained (Scheme 12). In the presence of phosphines, monomeric species such as 22 may be obtained. Other less-electrophilic allylic substrates such as allylic ethers and allylic alcohols also serve as precursors to nickel-Jt-allyl complexes in cataljdic procedures. However, these precursors are less widely used than allyl halides in the stoichiometric preparation of the Jt-allyl complexes. 

An advance by Mackenzie has made nickel-ji-aUyl complexes accessible from enals and enones.P In a reaction that is mechanistically analogous to Method 1 in Section 1.1.2.1, enals, when treated with bis(q" -cycloocta-l,5-diene)nickel(0) (2) in the presence of chlorosilanes, afford chloro-bridged dimeric q -aUylnickel complexes such as 25 (Scheme 14). Enones are less reactive in the process and require p5n idine to facilitate the oxidative addition. Rather than using bis(ti -cycloocta-l,5-diene)nickel(0) (2), a more convenient and less expensive alternative involves the in situ reduction of dichlorotetra-lds(p3n idine)nickel(II) (26) with sodium metal in the presence of cyclooctadiene to give enone-derived q -allylnickel complexes (e.g., 27). 

The 1 1 complex derived from phenyltungsten trichloride and aluminium trichloride is an effective catalyst for diene-cyclobutane metathetical interconversions. Thus, the tetracyclic compounds (291) and (292) were respectively isomerized to the dienes (293) and (294). Rather more surprising was the virtually quantitative formation of the cyclobutanoid compound (296) from (295). Reaction of norbomadiene with 2,2 -bipyridyl(cyclo-octa-l,5-diene)nickel at 25°C yielded the exo-trans,endo-metal o-carbocyclic (297) which, on treatment with an activated olefin (e.g. maleic anhydride), afforded the cyclo-dimer (298 predominantly exo-trans,endo) in good yield by displacement of the hydrocarbon moiety. Catalytic conversions can also be achieved. 

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