Cyclododecatriene complexes

The 1,2-azaphosphole i7 (P)-coordinated complexes 83 and 84 follow from the corresponding ligand and [(i -allyl)NiCl]2 and [(1,5,9-cyclododecatriene)Ni], respectively (98ICA(270)273). 

Butadiene could be oligomerized to cyclic dienes and trienes using certain transition metal complexes. Commercially, a mixture of TiCU and Al2Cl3(C2H5)3 is used that gives predominantly cis, trans, trans-1,5,9-cyclododecatriene along with approximately 5% of the dimer 1,5-cyclooctadiene ... 

Conjugated dienes can be dimerized or trimerized at their 1,4 positions (formally, [4 4- 4] and [4 4-4 4-4] cycloadditions) by treatment with certain complexes or other transition metal compounds. " Thus butadiene gives 1,5-cyclooctadiene and 1,5,9-cyclododecatriene. " The relative amount of each product can be controlled by use of the proper catalyst. For example, Ni P(OC6H4—o-Ph)3 gives predominant dimerization, while Ni(cyclooctadiene)2 gives mostly trimerization. The products arise, not by direct 1,4 to 1,4 attack, but by stepwise mechanisms involving metal-alkene complexes. " ... 

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). 

A m-RuCl2(CO)2(PPh3)2 complex, which catalyzes hydrogenation of dienes and monoenes, becomes useful in the presence of added phosphine for selective hydrogenation of 1,5,9-cyclododecatriene to cyclododecene the catalyst is a HRuCl(CO)2(PPh3)2 hydride that operates via steps analogous to those of reactions (9)-(11) (144, 145). 

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 ... 

Type [55] complexes are obtained from cyclooctadienes (74), too, but also from cy-clododecatrienes (59, 117), hexadienes (765), and butadienes (755). Some of these reactions also lead to tetraruthenium olefm clusters. Of these, the complex [7 ] has been mentioned already, and is obtained from cyclooctadiene (74, 75, 283), whereas the complex [59] results from cyclododecatriene (56, 59). 

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 ... 

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). 

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. 

In the absence of added phosphine the main product is the cyclic trimer of butadiene—cyclododecatriene. The presence of three double bonds in this molecule means other geometric isomers apart from the one shown in Fig. 7.6 exist. Identification of the species 7.31 by NMR is evidence for the involvement of rf-allyl intermediates. The complex 7.31 reductively eliminates 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...

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... 

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