Complex nickel-butadiene

Soluble single species catalysts are also known, such as the bis(7r-allyl nickel halides) [7]. These can be prepared separately or in situ by reacting bis-allyl nickel (which is an ologomerization catalyst for butadiene but does not give high molecular weight polymer) with an equimolar quantity of nickel halide, and thus bears some resemblance to the catalysts from titanium subhalides and alkyl titanium halides. It is of interest to note that the active species is the monomeric form of the initiator as TT-complex with butadiene (XII) [61]. 

REACTION PRODUCTS AND ORGANOMETALLIC INTERMEDIATES WITH NICKEL(0) COMPLEXES. Nickel(O) complexes such as (Cod)2Ni, show a striking parallel with lithium(0) complexes in their reactions with diphenylacetylene a sequence of monomolecular reduction bimolecular, stereospecific reduction and cyclotrimerization (Scheme IX). Consonant with the suggestion that nickel(0) forms nickelirene (26) and nickelole (27) intermediates in the course of cyclotrimerization of diphenylacetylene is the isolation of (Z)-l,2-di-phenylethene (28) and (E,E)-1,2,3,4-tetraphenyl-l,3-butadiene (29) upon hydrolysis. Furthermore, when DC1 was used in the workup, both 28 and 29... 

The nickel-butadiene complex deposited on PCl3-treated AI2O3 and activated with AlEtj shows good catalytic activity for the dimerization of propylene, giving predominantly 2-methyl-2-pentene in halogenated hydrocarbons and 4-methyl-2-pentene in pentane [618]. 

Nickel(O) forms a n-complex with three butadiene molecules at low temperature. This complex rearranges spontaneously at 0 °C to afford a bisallylic system, from which a large number of interesting olefins can be obtained. The scheme given below and the example of the synthesis of the odorous compound muscone (R. Baker, 1972, 1974 A.P. Kozikowski, 1976) indicate the variability of such rearrangements (P. Heimbach, 1970). Nowadays many rather complicated cycloolefins are synthesized on a large scale by such reactions and should be kept in mind as possible starting materials, e.g. after ozonolysis. 

DuPont currentiy practices a butadiene-to-adiponittile route based on direct addition of HCN to butadiene (6—9). It was first commercialized in 1971. AH reactions are catalyzed by soluble, air and moisture sensitive, ttiarylphosphite-nickel(0) complexes. 

One other reaction deserves mention. From bis(cyclooctadiene)nickel and butadiene (31), and in the presence of an isocyanide (RNC, R = cyclohexyl, phenyl, tcrt-butyl) two organic oligomeric products are obtained, 1 -acylimino-11 -vinyl-3,7-cycloundecadiene and 1 -acylimino-3,7,11 -cyclo-dodecatriene. In each, one isocyanide has been incorporated. An analogous reaction with carbon monoxide had been reported earlier. The proposed mechanism of these reactions, via a bis-7r-allyl complex of nickel, is probably related to the mechanism described for allylpalladium complexes above. 

Tindall D,PawlowJH,Wagener KB (1998) RecentAdvancesin ADMET Chemistry. 1 183-198 Tobisch S (2005) Co-Oligomerization of 1,3-Butadiene and Ethylene Promoted by Zerovalent Bare Nickel Complexes. 12 187-218 Tomioka K, see Iguchi M (2003) 5 37-60 Tomooka K, see Hodgson DM (2003) 5 217-250... 

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],... 

Structure-Reactivity Relationships in the Cyclo-Oligomerization of 1,3-Butadiene Catalyzed by Zerovalent Nickel Complexes... 

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... 

Scheme 6 displays the interplay of the two reaction channels for this type of nickel catalyst. The electronic and steric properties of the ancillary ligand are shown to have a pronounced influence on the kinetic and thermodynamic aspects of the VCH (via 2a 8a) and cis,cis-COD (via 4a 10a) generating routes (cf. Section 5.4) and will also affect the substitution process of the PR3/P(OR)3 ligand by incoming butadiene in the octadienediyl-Ni11 complex (vide infra). The species 2a and 2b are likely to... 

Scheme 6. Interplay of the C8- and C -production channels for the cyclo-oligomerization of 1,3-butadiene with zero valent PR3/P(OR)3-stabilized nickel complexes as the catalyst. Free energies (AG, AGJ in kcalmol-1) are given relative to the favorable rf-synrfiC A-cis isomer of 2a for catalysts bearing strong a-donor ligands namely I (L = PMe3), III (L = PPrj), VI (L = PBU3), and -acceptor ligands namely V (L = P(OMe)3), IV...

Among transition metal complexes used as catalysts for reactions of the above-mentioned types b and c, the most versatile are nickel complexes. The characteristic reactions of butadiene catalyzed by nickel complexes are cyclizations. Formations of 1,5-cyclooctadiene (COD) (1) and 1,5,9-cyclododecatriene (CDT) (2) are typical reactions (2-9). In addition, other cyclic compounds (3-6) shown below are formed by nickel catalysts. Considerable selectivity to form one of these cyclic oligomers as a main product by modification of the catalytic species with different phosphine or phosphite as ligands has been observed (3, 4). 

Linear oligomerization and telomerization of butadiene take place with nickel complexes in the presence of a proton source (7). In addition, cooligomerization of butadiene with functionalized olefins such as methacrylate is catalyzed by nickel complexes [Eq. (4)] (12, 13) ... 

Mechanistic studies of the nickel-catalyzed cyclization of butadiene have been carried out. The formation of various cyclic compounds catalyzed by nickel complexes is explained via the intermediacy of ir-allylic nickel complexes 11 and 12. 

Similar studies on the reactions of butadiene and bis(ir-allyl)palladium were carried out by Wilke and co-workers (4). Unlike the reactions with nickel complexes, no cyclization took place, and 1,6,10-dodecatriene... 

After that, studies on the palladium-catalyzed reactions of conjugated dienes attracted little attention. They have only been reexamined since the late 1960 s. The scope of the reaction of butadiene catalyzed by palladium complexes has gradually been established. The catalysis by palladium is different from those of other transition metals. Although palladium is located below nickel in the periodic table, the catalytic... 

These telomerization reactions of butadiene with nucleophiles are also catalyzed by nickel complexes. For example, amines (18-23), active methylene compounds (23, 24), alcohols (25, 26), and phenol (27) react with butadiene. However, the selectivity and catalytic activity of nickel catalysts are lower than those of palladium catalysts. In addition, a mixture of monomeric and dimeric telomers is usually formed with nickel catalysts ... 

Unlike nickel Catalysts, palladium complexes do not catalyze the homo-cyclization reaction to give CDT or COD. The difference seems to be due to a different degree of hydride shift and atomic volume. With palladium catalysts, the hydride shift is easier, and hence linear oligomers are formed. The characteristic reaction catalyzed by palladium is the cocyclization of two moles of butadiene with one-hetero atom double bonds such as C=N and C=0 bonds to give six-membered rings with two vinyl groups (19) ... 

With nickel complexes, these cocyclizations are not possible. A related reaction is the cocyclization of butadiene with azines to give 12-mem-bered heterocyclic compounds 9 (11) [see Eq. (3)]. 

Recently, the heterogenization technique has allowed more-selective reactions to be observed. For example, butadiene gives 95% of 1,3,6-octatriene (example 28 in Table 1) on a catalyst obtained by reduction of NiBr2(supported phenylphosphines)2 with NaBH4 (44). Nickel-carbonyl complexes have also been supported on phosphinated silica (55). 

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