Oligomerization of acetylene

Cuprous salts catalyze the oligomerization of acetylene to vinylacetylene and divinylacetylene (38). The former compound is the raw material for the production of chloroprene monomer and polymers derived from it. Nickel catalysts with the appropriate ligands smoothly convert acetylene to benzene (39) or 1,3,5,7-cyclooctatetraene (40—42). Polymer formation accompanies these transition-metal catalyzed syntheses. 

Figure A Cyclic oligomerizations of acetylene tetramerization producing cyclooctatetraene (cot) and trimerization producing benzene.

Group 10 transition metal catalysts including Ni and Pd are known as a new class of catalysts for the polymerization of substituted acetylenes, but the reports treating these catalysts are still not many. Some of the reports in an early stage displayed that the group 10 catalysts rather induce cyclic and linear oligomerizations of acetylene monomers. Thus, only fragmental information is available in some of the papers. 

Some preliminary work on the oligomerization of acetylenes, particularly ethylpropiolate and phenylacetylene, using supported nickel(O) catalysts has been reported (4, 15, 30). The initial products appear to be benzene derivatives (4, 30), although one group (30) reports that reuse of the catalyst yielded some cyclooctatetraene derivatives on the second... 

L. Mond and his co-workers discovered it in 1888. The platinum methyls, prepared in 1907 by W. J. Pope, were amongst the first-known transition metal alkyls, and the discovery by W. Reppe in 1940 that Ni complexes catalyse the cyclic oligomerization of acetylenes produced a surge of interest which was reinforced by the discovery in I960 of the jr-allylic complexes of which those of Pd arc by far the most numerous. 

The experimental observations are summarized in Scheme 19 the Fe -catalyzed oligomerization of acetylene becomes rapid once three C2H2 units have assembled around the metal ion but slows down upon addition of a fourth molecule, showing that further polymerization requires a substantial barrier. ... 

Cyclopentadienylbis(triphenylphosphine)cobalt catalyzes the oligomerization of acetylenes and cooligomerization of acetylenes and nitriles or acetylenes and isothiocyanates, RNCS " [scheme (9.165)]. 

Triphenylchromium(III) causes trimerization of acetylenes leading to the formation of arene complexes (cf. reactions of oligomerization of acetylenes. Chapter 6) see equation (10.18). 

Bis(1,5-CyclOOCtadiene)nickel(0). This complex can be used for the oligomerization of acetylene and the dimerization of dienes such as butadiene. It is prepared by the reaction of nickel(II) (2,4-pentanedionate) and triethylalu-minum with cyclooctadiene (7). 

SCHEME 21.3 The cyclotrimerization of acetylene to form benzene (a), and the oligomerization of acetylene... 

Reviews in this area are concerned with the oligomerization of acetylenes induced by... 

Reyiews.—Recent reviews on areas of acetylenic chemistry include synthetic routes to average-ring-size cycloalkynes, a study of the bonding in metal-acetylene complexes, transition-metal complexes of acetylene, intramolecular cyclization reactions with acetylenic bond participation, oligomerization of acetylenes induced by metals of the nickel triad, an article on the handling of acetylenic compounds, and a book on preparative acetylenic chemistry. ... 

Several examples of poly- and oligomerization of acetylenes are also quite typical. Water-soluble rhodium complexes with hydrophilic phosphine ligands catalyze the polymerization of arylacetylenes into stereoregular cis-oriented poly(arylacetylenes), which can further be selectively depolymerized on heating to provide a convenient method for the preparation of triaryl-benzenes [194]. Different types of product formed by regioselective di- and trimerization can be obtained by the reaction of such catalysts with other kinds of terminal acetylenes [195]. 

P. M. Maitlis, The Palladium(ii)-Induced Oligomerization of Acetylenes An Organometallic Detective Story , Accounts Chem. Res., 1976, 9, 93. 

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