Nickel complexes cyclododecatriene

Nickel-triarylphosphite complexes catalyze the dimerisation of butadiene to cyclooctadiene. Cyclododecatriene is an unwanted by-product, which results from trimerization catalyzed by the same catalyst. Table 3.2 shows the product yields using various ligand-metal complexes (the remainder in each case is a tarry polymeric material). 

Scheme 7.3 Preparation of (fl//-franj-l,5,9-cyclododecatriene)nickel(0) (12) and its reactions with all-cis-C12H18 to the isomer 13 and with 1,5-cyclooctadiene to the bis(diolefin) nickel(0) complex 14...

Nickel(O) complexes also catalyze a variety of cyclooligomerizations of butadiene. Hiis process, studied intensively by Wilke and Jolly and co-workers, can lead to a myriad of products that depend on the reaction conditions (Scheme 22.22). The cyclotrimerization of butadiene to cyclododecatriene was one of the first organometaUic reactions subjected to careful mechanistic studies, and these studies led to the proposal that tiiis process occurs by the mechanism shown in Scheme 22.23. Again, the bis-ri -allyl complex containing 12 carbon atoms was isolated and characterized. It has been shown to enter the catalytic cycle as shown. 

Some olefin complexes may conveniently be obtained by electrochemical reduction methods. Cyclooctadiene and cyclododecatriene nickel(O) complexes such as Ni(COD)2 and Ni(CDT) may be prepared by electrochemical reduction of nickel acetylacetonate in the presence of butadiene in acetonitrile, dimethoxymethane, or DMF solutions. Complexes [Fe(CO)4 (alkene)] are reduced electrochemically to lie compounds [Fe(CO)3 (alkene)] . In the case of complexes [Fe(CO)3 (f/Miene)] (diene = BD, cyclohexadiene), during reduction, lie anions [Fe(CO)3 (diene)] are formed in which one olefin bond is decomplexed. ... 

The nickel(O) complexes are effective in cyclooligomerization of butadienes. The complexes XII and XIII have been demonstrated to be intermediates in the catalytic oligomerization of butadiene the ligand displacement reaction of XII gives a mixture of 1,2-divinylcyclobutane, 4-vinylcyclohexene, and 1,5-cyclooctadiene (Brenner et al., 1969 Heimbach and Wilke, 1969), whereas complex XIII affords 1,5,9-cyclododecatriene (Wilke, 1963 Bogdanovic et al., 1969). Similarly, a number of bis(it-cyclo-... 

Nickel(O) reacts with the olefin to form a nickel(0)-olefin complex, which can also coordinate the alkyl aluminum compound via a multicenter bond between the nickel, the aluminum and the a carbon atom of the trialkylaluminum. In a concerted reaction the aluminum and the hydride are transferred to the olefin. In this mechanistic hypothesis the nickel thus mostly serves as a template to bring the olefin and the aluminum compound into close proximity. No free Al-H or Ni-H species is ever formed in the course of the reaction. The adduct of an amine-stabihzed dimethylaluminum hydride and (cyclododecatriene)nickel, whose structure was determined by X-ray crystallography, was considered to serve as a model for this type of mechanism since it shows the hydride bridging the aluminum and alkene-coordinated nickel center [31]. 

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). 

Significant advances in organonickel chemistry followed the discovery of frtzws,fraws,fraws-(l,5,9-cyclododecatriene)nickel, Ni(cdt), and bis(l,5-cycloocta-diene)nickel Ni(cod)2 by Wilke et. al.1 In these and related compounds, in which only olefinic ligands are bonded to the nickel, the metal is especially reactive both in the synthesis of other compounds and in catalytic behavior. Extension of this chemistry to palladium and to platinum has hitherto been inhibited by the lack of convenient synthetic routes to zero-valent complexes of these metals in which mono- or diolefins are the only ligands. Here we described the synthesis of bis(l,5-cyclooctadiene)platinum, tris(ethylene)-platinum, and bis(ethylene)(tricyclohexylphosphine)platinum. The compound Pt(cod)2 (cod = 1,5-cyclooctadiene) was first reported by Muller and Goser,2 who prepared it by the following reaction sequence ... 

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 ... 

Wilke and his co-workers have shown that zera-valent complexes, especially of nickel, obtained by reduction with aluminium alkyls can be used in a wide variety of polymerisations such as trimerisation of butadiene to trans, tran, trans-cyclododecatriene. 

It has been known for many years that the key intermediate in the cy-clotrimerization of butadiene to 1,5,9-cyclododecatriene is an Tj3,i73-do-decatrienediyl nickel species (73). We have recently reinvestigated this complex in the hope of obtaining further structural information, and the 13C-NMR spectrum is shown in Fig. 9. The spectra in THF-dg and toluene-t(8 are practically identical, indicating that THF is not here functioning as a ligand. The spectrum shown in Fig. 9 was run in THF-dg and... 

Two isomeric 1,5,9-cyclododecatrienes, namely, trans,trans,cis-CijH 18 (XLVI) and trans,trans,trans-CuHis (XLVII), are formed in good yield by the cyclic trimerization of butadiene using certain Ziegler-type catalysts 247, 250, 251, 252). The formation of these 12-membered ring hydrocarbons probably proceeds via metal 7r-complexed intermediates. When the cyclic triene (XLVII) is treated with nickel acetylacetonate and... 

Cyclododecatrienes likewise form tt complexes with transition metals such as silver, copper, palladium, etc. Details of these studies, as well as the work on nickel complexes described above, are contained in the recent monograph by Fischer and Werner 100),... 

What compounds are the active catalysts in this process By this method of catalyst preparation we do not obtain a mixture of indefinite composition, but TT-complexes which can be isolated and are mostly crystalline. If, for instance, nickel acetylacetonate is reduced in the presence of P(CeH5)3 we obtain a new compound, Ni-(0)-[P(CeH5)3]4. This compound is itself an active catalyst for the cyclo-oligomerization of butadiene, producing about 65 to 70% cyclo-octadiene, 20% vinylcyclohexene, and 10% cyclododecatriene. Instead of P(CeH5)3 we can introduce As(CeH5)3 and isolate Ni-(0)-[As(CeH5)3]4 as an active cata-... 

The next step was to investigate the reaction of the centro-nickel compound wdth butadiene. When a solution of this compound is saturated with butadiene at room temperature, we observe that after a certain period the excess of butadiene has reacted with formation of cyclododecatriene and a new complex which can be isolated by removing the cyclododecatriene under high vacuum. The same catalytic reaction can be carried out by using bis (1,5-cyclo-octadiene) nickel as a catalyst. Cyclododecatriene synthesized in this way consists of three isomers. The main product is trans,trans,trans-cyc ododecdAx ene and the isolated by-products are transytrans,cis- and cis,cis,trans-cyc ododec3itnene. The latter compound is a new isomer, previously imknown (b.p.14 110° C., 1.5129). The synthesis of... 

The intermediate complex mentioned above can be prepared in a very pure state if the centro-nickel compound is treated at —40° C. with an excess of butadiene. Also in this case the cyclododecatriene will be displaced, but no catalytic reaction takes place, and if the excess butadiene is removed at low temperature. 

Reaction with CO at —60° C. yielded nickel carbonyl and a Ci3 ketone. Addition of one mole of P(C2H5)3 formed a crystalline complex which was identical with the compound obtained from cyclododecatriene-centro-nickel and... 

Finally, the addition of one molecule of P(C2H5)3 induces an electron miration with formation of cyclododecatriene. No displacement occurs and the prodfuct obtained is identical to that prepared from the cyclododecatriene-centro-nickel complex itself ... 

The best known example is the cyclization of butadiene and acetylene 121 14°). Butadiene forms cyclooctadiene and cyclododecatriene by the catalytic action of nickel, iron, and other metal complexes. By an experiment using an iron complex with deuterated butadiene, it was proved that no hydrogen shift takes place in the cyclization reaction 70>. 

Co2(CO)s reacts with propargyl alcohols giving benzenic cyclotrimers and dehydrated oligomers.By contrast, (CDT)Ni (CDT = cyclododecatriene) reacts with alkynes to give homoleptic trinuclear clusters. No dehydration occurs during the formation of these complexes it is worthy of note that diols do not react with nickel. 

The complex Ni(7r-l,5-CgHi2)2, presumably a tetrahedral complex of Ni(0), has been obtained as air-sensitive, yellow crystals by ligand displacement from Ni(cyclododecatriene), or by reducing nickel acetylacetonate with alkyl aluminums in the presence of the diene 133). Derivatives such as CgHi2Ni(acac) and CsHi2Ni(PPh3)2 have also been mentioned 134). This work is summarized elsewhere 124). 

The nickel complex with /,f,f-cyclododecatriene is also trigonal it may be obtained by reaction of [Ni(C3H5)2] with butadiene first affording an allyl complex, which subsequently undergoes cyclization to form the olefin compound. 

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