Nickel, chloro-, dimer

A transient orange complex is formed in this reaction, which is very probably chloro-/i3-allylnickel(l 1) dimer, a complex that can be obtained from nickel carbonyl and allyl chloride in an inert solvent (8). The probable mechanism of the carbonylation then becomes clear with the additional facts that bromo-fi3-allylnickel(Il) dimer reacts with carbon monoxide to give unstable bromodicarbonyl(3-butenoyl)nickel(II), which then reacts further with CO to form nickel carbonyl and 3-butenoyl bromide (6). Six separate steps are believed to be involved ... 

Nonregioselective dimerization is widely used on an industrial scale for propene, n-butenes and ethylene (Institut Fran9ais du Petrole s Dimersol process). The catalyst results from the interaction of a nickel organic salt, soluble in a paraffinic hydrocarbon solvent, and an ethylaluminum chloro compound the active species is formed in situ inside the dimerization reactor. 

Nickel-catalyzed stereospecific cyclocarbonylation of cWo-cyclopentadiene dimer 3 with ( )-l -chloro-2-butene, carbon monoxide and tetracarbonylnickel in acetone/water at room temperature gives a-methyl-3-oxotetracyclo[5.5.1.02,6.08,12]tridec-9-ene-4-aceticacid (4)in 10% yield51. An X-ray investigation of the acid reveals a selective cis-exo attack at the strained double bond, while the other double bond does not react. The exo dimer of cyclopentadiene gives a different product, thus there is no isomerization, in contrast to reactions under acidic conditions. 

A typical reaction involving nickel(O) treats an allylic halide such as 3-chloro-2-methyl-l-propene with Ni(CO)4 to form 439,288 a nickel dimer analogous to the palladium chloride dimer discussed in the previous section. This complex reacts with an alkene to form a new complex (440), and subsequent reaction with a variety of electrophilic reagents removes nickel. In this example, the chlorine was converted to an acetate ligand (in 441) and reacted with methanolic carbon monoxide to give the ester (442).288... 

An advance by Mackenzie has made nickel-ji-aUyl complexes accessible from enals and enones.P In a reaction that is mechanistically analogous to Method 1 in Section 1.1.2.1, enals, when treated with bis(q" -cycloocta-l,5-diene)nickel(0) (2) in the presence of chlorosilanes, afford chloro-bridged dimeric q -aUylnickel complexes such as 25 (Scheme 14). Enones are less reactive in the process and require p5n idine to facilitate the oxidative addition. Rather than using bis(ti -cycloocta-l,5-diene)nickel(0) (2), a more convenient and less expensive alternative involves the in situ reduction of dichlorotetra-lds(p3n idine)nickel(II) (26) with sodium metal in the presence of cyclooctadiene to give enone-derived q -allylnickel complexes (e.g., 27). 

The synthesis of 1,5-dienes via the reaction of allyl halides and nickel carbonyl is now an indispensable process in synthetic organic chemistry. To our knowledge, it originates from the observation by Webb and Borcherdt (1951) that the reaction of l-chloro-2-butene or 3-chloro-l-butene with nickel carbonyl produced the dimeric 1,5-dienes in high yield. Later Corey and his... 

Supramolecular systems assembled by peripheral and axial coordination were also thoroughly described. For example, heteroarrays held by axial coordination, particularly of zinc, nickel, ruthenium, tin, silicon, etc. porphyrins and phthalo-cyanines to peripheral pyridyl and 4,4-bipyridyl groups were described. Another interesting class of compounds are porphyrin dimers prepared by coordinative assembly of cw- icso-(4-pyridyl)porphyrins with PdCla forming two [PtCl2(pyP)2] complexes, and more complex tesselated structures by substitution of the platinum complex chloro ligands by 2,3-diamine(azaporphyrins), as depicted in Fig. 12. 

The formal cyclooligomerization of vinylidene units via copper or nickel car-benoids represents another route to [4]radialenes. To this end, a l,l-dibromo(or chloro)-alkene can be converted into a bis(l-halogenovinyl)cuprate at low temperatures, which, on warming, furnishes the [4]radialene, often accompanied by the corresponding dimerization product, the [3]cumulene. This method is so far the only route to octaphenyl[4]radialene (see Scheme 4.10, Section 4.2.1) and other octaaryl[4]radialenes [10, 37]. With l,l-dibromo-2-methylprop-l-ene (32) as the starting material, a mixture of [4]radialene 71 and [Sjradialene 84 as the major products is formed [76] (Scheme 4.17). While this method is not the preferred route to the former radialene, it represents the only known way for the preparation of 84. Treatment of dibromoalkene 32 with a Ni(0) complex [37] or activated nickel [10] does not improve the yield of radialene 71. 

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