Cyclododecatriene complexes with nickel

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),... 

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 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. 

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). 

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. 

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...

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 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). 

Butadiene reacts with cyclododecatriene-nickel or bis(cyclooctadiene)-nickel at 20° C, replacing the olefinic ligands and forming a new molecule of cyclododecatriene (99), In this reaction atomic nickel must be the catalyst, as it is in some reactions of bis(acrylonitrile)-nickel. Most of the catalytically formed cyclododecatriene has the trans-trans-cis configuration, but, small amounts of the trans-cis-cis isomer have also been detected. When the reaction between (LIV) and butadiene was carried out at — 40°C. Wilke et al. were able to isolate an intermediate (LVI) the nature of which was of great importance in elucidating reaction mechanism. Complex (LVI) is actually a bis(7r-allyl)-nickel type of compound involving a twelve-carbon-atom chain, formed by condensation of three molecules of butadiene. Ally ... 

The conversion of the C12 chain in (LVI) to cyclododecatriene can also be achieved by treating (LVI) with electron donors such as carbon monoxide, phosphines, or even butadiene. With phosphines under mild conditions the ring closure to cyclododecatriene takes place without decomposition of the complex and cyclododecatriene-nickel-phosphine adducts are isolated (99). With carbon monoxide at — 60° C (LVI) affords a vinylcycloundecadienone (LVII) (99). 

The insertion of carbon monoxide has not yet been achieved. Bis(ir-allyl)-nickel reacts with butadiene to form cyclododecatriene. The allylic groups may also be displaced by cycloocta-l,5-diene or cyclooctatetraene. Wilke regards (LVIII) as formally a complex of Ni(II), assuming that during the catalysis there is a constant and reversible change in the formal oxidation... 

The second distinct observation involves hydrogenation of weakly bound olefin complexes in which hydrogenation is complete and the metal TT-complex is destroyed. For example 1,5,9-cyclododecatriene-centro-nickel(O) absorbs hydrogen very readily, producing cyclododecane and metallic nickel. The ease of hydrogenation has led to the assignment of a zero valent nickel loosely associated with three double bonds, equation (6-25). 

The concept of constrained geometry is also important and this is why 7i-complexes of metal and olefins can lead to structured molecules. For example a model of cyclododecatriene-nickel shows that the nickel atom is situated exactly in the center of the ring. This picture represents a lock and key fit very precisely another analogy with an enzyme-substrate complex. 

Treatment of nickel acetylacetonate with aluminium alkyls in the presence of cyclododecatrienes or butadiene, or of bis-)p-allyl nickel with butadiene, gives cyclododecatriene nickel, a volatile blood-red crystalline compound 10.6.This 16-electron nickel complex reacts catalytically and very rapidly with butadiene at 20° liberating isomers of cyclododecatriene. The major product is the trans-trans-cis isomer small amounts of the trans-cis-cis isomer are also formed. If the reaction with butadiene is carried out at -40° the bis-w-enyl complex, 10.7, is isolated in which the ligand is the same as that found in the complex formed from butadiene and ruthenium salts (p 180). The carbonylation (Figure 53) provides evidence for the... 

Treatment of nickel acetylacetonate with alkylaluminiums in the presence of cyclododecatrienes or butadiene, or treatment of bis- r-allyl nickel with butadiene, gives cyclododecatriene nickel, a volatile blood-red crystalline compound, 9.4 [71, 72, 73]. This 16-electron nickel complex reacts... 

---