Cyclooctatetraene with cyclopentadiene

It has recently been reported83 that di-n-cyclooctatetraene complexes of uranium, thorium, and plutonium can be prepared by the direct reaction of the finely divided metals with cyclooctatetraene. The finely divided metals were prepared by a procedure described by Seaborg and Katz.84 Several cycles of formation and descomposition of the hydride gave a finely divided reactive metal. However, treatment of the pyrophoric uranium with cyclopentadiene under the same conditions used to form uranocene failed to produce any detectable amounts of the known compounds U(CsH5)3 or U(C5H5)4. 

Attempts have been made to trap the free cyclobutadiene supposedly formed in the phosphine reaction with cyclopentadiene or methyl phenyl-propiolate 24,25). While the expected adducts (LXXV) and (LXXVI) were isolated, the yields, < 10%, were so small as to make it doubtful that any appreciable amount of free tetraphenylcyclobutadiene, a highly reactive species, was actually present under these reaction conditions in the presence of a large excess of the diene or dienophile. The main product in the second reaction was again the cyclooctatetraene (XLIII). 

Ru3(CO) 2 reacts with cyclooctadiene or cyclooctatetraene to afford the ring compounds coordinated by four electrons as shown in eqs. (16.14) and (16.15) [8,23]. However, in the reaction with cyclopentadiene, since the four-electron... 

Of the cyclic olefins, norbornadiene replaces two CO groups from one Co to yield a labile complex 159, 160, 235), cyclooctatetraene replaces the axial CO ligands from all three cobalt atoms 53) and is itself replaced by other Lewis bases 330), and cyclopentadiene forms the unusual complex [95] with Co3(CO)gCMe 159,160). A few catalytic reactions were observed with methinyltricobalt enneacarbonyls including the dimerization of norbornadiene 160, 235) and the polymerization of functional olefins 312) with different Co3(CO)9CX. 

The paper is divided into six parts, an abstract, and an appendix with mathematical details. Part 1 gives an introduction and outline of the problem, which shows that the physicist Erich Huckel had a pronounced knowledge about the chemical and physical properties of aromatic compounds. The chemical knowledge was certainly aquired from discussions with his brother Walter Huckel, who was a chemistry professor and textbook author [14]. Huckel discusses benzene, pyridine, pyrrol, furan, thiophene, isomeric forms of dihydrobenzene and chinone, cyclobutadiene, cyclooc-tatetraene, and cyclopentadiene. He points out that there is no satisfactory explanation for the observation why cyclobutadiene does not (at that time) exist, and why benzene and cyclooctatetraene are stable but chemically very different in their reactivity. Huckel emphasizes that the number 6 appears to play a particular role for aromatic compounds, which had been pointed out for the first time by Bamberger in 1890 [15]. 

Two distinct observations are made with respect to the hydrogenation of olefin 7i-complexes with catalysts such as raney nickel. When the olefin is firmly bound to a metal, complete catalytic hydrogenation is prohibited. Thus 7i-cyclopentadienylcobalt cyclooctatetraene (6-22), 7r-cyclopentadienyl tt-cyclopentadiene rhenium dicarbonyl (6-23), and Tr-cycloheptatriene iron tricarbonyl (6-24), each of which contains at least one uncomplexed double bond, readily undergo hydrogenation of the uncomplexed bonds only. The metal-olefin bond is preserved in each case. 

Cookson et al. first reported prior to 1965 that photochemical reaction of the Diels-Alder endo-adducts of cyclopentadiene or cyclohexa-1,3-diene with p-benzoquinone gave cage compounds by formation of a cyclobutane ring from the two double bonds. Irradiation of an ethyl acetate solution of the cyclopentadiene adduct 36 with a medium pressure Hg lamp for 6 h afforded cage 37 (90%). This photoreaction proceeded even in the soHd state, and the cage compound 37 was obtained in 80% yield after 80 h irradiation. Similarly, the 1 1 adduct 38 of cyclohexa-l,3-diene and p-benzoquinone was converted into cage 39 by irradiating the ethyl acetate solution for 10 h (80%) or the soHd state for 90 h (90%). This reaction was successfully appKed to the adduct 40 of cyclooctatetraene (COT) and p-benzoquinone (92%... 

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