Cyclopentadiene complexes cyclooctatetraene

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. 

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. 

A wide variety of other conjugated diolefins have been shown to form (C4)M-type bonding systems. These include cyclopentadiene, cyclopenta-dienone, cyclohexadiene, cycloheptatrienone, and cyclooctatetraene. The bands attributed to the free olefin, appearing at 1575-1600 cm Mn the free olefins, display a typical bathochromic shift (to 1500-1460 cm" ) in their complexes. If one double bond of the diolefin is complexed while the second remains free, often two well-separated absorptions are observed, one being in the region of an uncomplex olefinic linkage and the other at a lower frequency (Table 4-5). 

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. 

An interesting extension of the chemistry in this field is the preparation of mixed cyclopentadiene-cyclooctatetraene complexes (Jamerson et al., 1974) according to the reactions... 

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