Nickel complexes cyclo-octadiene

Among many examples of -orbital interaction, only the following two are selected to illustrate the feature of HO—LU conjugation. One is the cyclooctadiene-transition metal complex ">. The figure indicates the symmetry-favourable mode of interaction in a nickel complex. The electron configuration of nickel is (3d)8 (4s)2. The HO and LU of nickel can be provided from the partly occupied 3d shell from which symmetry-allowed occupied and unoccupied d orbitals for interaction with cyclo-octadiene orbitals are picked up. 

The electrochemical technique has been relatively rarely applied to obtain the metal 7i-complexes [202,506,507], Thus, the electrosyntheses of complexes of copper with cyclo-octadiene and nickel with cyclo-octatetraene were reported [202,506,507]. The electrochemical reactions (3.242) are of especial interest, since they allow us to produce fe-cyclopentadienyl complexes [563-565] ... 

Either triphenylarsonium benzoylylide or dibenzoylylide form complexes with bis(l,5-cyclo-octadiene)nickel these oligomerise ethylene under mild conditions . The dibenzoyl derivative is the more effective catalyst of the two, this being ascribed to the greater stabilization provided by the second benzoyl group the monobenzoyl derivative provides largely linear alkenes, but the dibenzoyl derivative leads to decreased linearity in the products. 

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... 

Ullmann reaction Semmelhack (4, 33) has shown that bis( 1,5-cyclo-octadiene)nickel(O) and tetrakis(triphenylphospine)nickel(0) are useful reagents for coupling of aryl halides (Ullmann reaction). However, these zerovalent nickel complexes are not easy to prepare and are extremely sensitive to moisture. Kende reasoned that the coordinatively unsaturated Ni(TPP)3 is actually the species involved and indeed found that aryl halides couple to biaryls in the presence of 1 eq. of this complex. Aryl halides with two orr/io-substituents do not couple. Otherwise, yields of biaryls are in the range of 60-80%. 

The reaction of bis(cyclo-octa-l,3-diene)nickel with hexafluorobut-2-yne gives (cyclo-octadiene)nickel[(hexakistrifluoromethyl)benzene], (114) or (115), which decomposes slowly at room temperature. Other ligands can displace the cyclo-octadiene, and alternative routes to some of the compounds are also reported, including the novel displacement of ethylene from (Ph3P)2Ni(C2H4) by preformed hexakis(trifluoromethyl)benzene. The compounds are formulated either as formally five-co-ordinate nickel complexes, with the planar arene occupying three co-ordination positions and free... 

Palladium complexes catalyse similar reactions, usually under milder conditions than those required using nickel. Azelaic acid (nonanedioic acid), which is an intermediate in the synthesis of the speciality nylon 6,9, is obtained from butadiene via 1, 5-cyclo-octadiene. 

Aliphatic nitriles react slowly with phenols and phenyl ethers in the presence of trifluoromethanesulphonic acid to give ketones after hydrolysis, in a variation of the Houben-Hoesch reaction. The crystalline complex of copper(i) triflate and benzene induces the acylation of aromatic substrates with selenol esters, affording a transition-metal mediated version of the Friedel-Crafts reaction. Aromatic carboxylic acids can be converted into symmetrical diaryl ketones in good yield by treatment of their 5-(2-pyridyl)thioesters with bis-(l,5-cyclo-octadiene)nickel [equation (15)]. In contrast to other methods for preparing symmetrical aromatic ketones, this method allows their preparation from a single starting material. 

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