Cyclooctatetraenes tetramerization

Cyclooctatetraene can be obtained on an industrial scale by metal carbonyl catalyzed thermal tetramerization of acetylene. If cyclooctatetraene is UV-irradiated at low temperature in the presence of acetone, it is reversibly rearranged to form semibullvalene (H.E. Zimmerman, 1968, 1970). 

Gyclooctatetraene (GOT). Tetramerization of acetylene to cyclooctatetraene [629-20-9], CgHg, although interesting, does not seem to have been used commercially. Nickel salts serve as catalysts. Other catalysts give ben2ene. The mechanism of this cyclotetramerhation has been studied (4). 

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

Both compounds were first synthesized in this way by Reppe Ni(II) salts were shown to be active in the formation of benzene,61 whereas cyclooctatetraene was isolated as the main product with zerovalent phosphinonickel complexes.62 No styrene was, however, obtained in the tetramerization, although it was the sought-after product by Reppe. 

In the tetrameric chloride crystal, the ring is puckered, with S symmetry, though with equal bond lengths round the ring (43). This may be contrasted with the most recent data for cyclooctatetraene, which has... 

All monomer syntheses begin with cyclooctane, which is obtained either by tetramerization of acetylene to cyclooctatetraene or by dimerization of butadiene to cyclooctadiene, with subsequent hydrogenation to cyclooctane. The cyclooctane is then converted into capryllactam either via the ketone and the oxime or through photoximation with NOCl (cf. nylon 6). Polymerization occurs as for nylon 6. 

Through an apparently less complicated process that nonetheless requires com-plexation with an organometallic catalyst, ethyne (acetylene, HC CH) itself undergoes trimerization in the presence of dicobalt octacarbonyl [Co2(CO)g] (Equation 6.69) to benzene and (Equation 6.70) tetramerization in the presence of nickel(II) cyanide [Ni(CN)2] to cyclooctatetraene. 

Cyclooctatetraenes (COTTs) have been the targets of intensive experimental and theoretical studies. Since the discovery of the Ni-catalyzed tetramerization of ethyne affording cyclooctatetraene by Reppe in 1948, transition-metal-mediated methodologies to this type of compounds still remain privileged [62]. To remedy the regioselectivity issue when simple alkynes are employed, Wender and Christy have developed [2-I-2-I-2-I-2] cycloadditions of 1,6- and 1,7-diynes under conditions that favor COTTs over competing [2-1-2-1-2] cycloadditions leading to benzene derivatives (Scheme 8.40) [63]. 

Nakamura Y, Aratani N, Shinokubo H, Takagi A, Kawai T, Matsumoto T, Yoon ZS, Kim DY, Ahn TK, Kim D, Muranaka A, Kobayashi N, Osuka A (2006) A directly fused tetrameric porphyrin sheet and its anomalous electronic properties that arise from the planar cyclooctatetraene core. J Am Chem Soc 128 4119 127... 

This polymerization has beei very successfully used to form several precursor polymers which will be discussed later. However ROMP has been applied to the direct synthesis of conjugated polymers as well, namely polyacetyloie. In this case, the appropriate monomer is a drde of 4 double bonds cyclooctatetraene (COT). This monomer, prepared by the tetramerization of acetylene with a nickel catalyst, has been polymerized, first using so-called "dcissical" but also Lewis-addle catalysts which... 

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