Cyclooctatrienyl

Homoaromaticity is a term used to describe systems in which a stabilized cyclic conjugated system is formed by bypassing one saturated atom. The resulting stabilization would, in general, be expected to be reduced because of poorer overlap of the orbitals. The properties of several such cationic species, however, suggest that substantial stabilization does exist. The cyclooctatrienyl cation is an example ... 

Cyclooctatrienyl Cyclopentadienyl Camphorsulfonic acid Cetyltrimethylammonium bromide... 

S,3R-(+)-4-dimethylamino-1,2-diphenyl-3-methylbutan-2-ol 1,5-Cyclooctadienyl 1,3 5-cyclooctatrienyl Cyclopentadienyl Camphorsulfonic acid cetyltrimethylammonium bromide... 

This reaction with cyclic olefins has produced some interesting carbonium species a topical example is the C8H9 ligand. This has been complexed to iron as bicyclic cyclooctatrienyl (64, 144, 221), and to molybdenum as a monocyclic homocarbonium ion (247). The latter is an example of a non-classical carbonium ion. 

Compared to the cyclooctatetraenyl dianion 19, other cyclic anions (besides cyclopentadienyl anions discussed in Sect. 1.5) have received considerably less attention. Of those that have been studied, not all of them display electron photoejection as a reaction pathway. For example, the 8,8-dimethyl-2,4,6-cyclooctatrienyl anion 22 undergoes cyclization to give 8,8-dimethylbicy-clo[5.1.0]octa-3,4-dienyl anion 23 on photolysis as the exclusive photochemical pathway [42] (Eq. 6). Photolysis of the cyclononatetraenyl anion 24 results in protonation of the more basic excited state anion, to give transient cis, cis, cis, cis-1,3,5,7-cyclononatetraene 25 (Eq. 7), which subsequently undergoes intramole-... 

Spectroscopic investigation (227) of the cyclooctatetraene complex (CgHg)PdCl2 indicates that all double bonds in the molecule are coordinated, but the structure of the complex has not been determined. When suspended in methanol, this complex is rapidly solvolyzed to produce (1, - dichlorobis(2 - methoxy - 3,5,7 - cyclooctatrienyl)dipalladium(II) (501). Similar complexes are formed by the reaction of 1,3-cyclohexa-diene, 1,3-cycloheptadiene, or 1,3- or 1,5-cyclooctadiene with Na2PdCl4 in methanol at room temperature. The last species reacts with HCl to give (l,5-cyclooctadiene)dichloropalladium(II) (501). Pyrolysis of the complex [(CgHi20CHa)PdCl]2 obtained from 1,5-cyclooctadiene yields 1-methoxy- and 2-methoxy-l,3-cyclooctadiene (535). 

Many studies used radiation chemistry to produce the radical and radical cations and anions of various dienes in order to measure their properties. Extensive work was devoted to the radical cation of norbomadiene in order to solve the question whether it is identical with the cation radical of quadricyclane . Desrosiers and Trifunac produced radical cations of 1,4-cyclohexadiene by pulse radiolysis in several solvents and measured by time-resolved fluorescence-detected magnetic resonance the ESR spectra of the cation radical. The cation radical of 1,4-cyclohexadiene was produced by charge transfer from saturated hydrocarbon cations formed by radiolysis of the solvent. In a similar system, the radical cations of 1,3- and 1,4-cyclohexadiene were studied in a zeolite matrix and their isomerization reactions were studied. Dienyl radicals similar to many other kinds of radicals were formed by radiolysis inside an admantane matrix. Korth and coworkers used this method to create cyclooctatrienyl radicals by radiolysis of bicyclo[5.1.0]octa-2,5-diene in admantane-Di6 matrix, or of bromocyclooctatriene in the same matrix. Williams and coworkers irradiated 1,5-hexadiene in CFCI3 matrix to obtain the radical cation which was found to undergo cyclization to the cyclohexene radical cation through the intermediate cyclohexane-1,4-diyl radical cation. 

The homotropylium cation, easily available to protonation of cycloocta-tetraene (121), has attracted considerable attention, particularly due to its non-classical homoaromatic structure (1). Two pathways can be discerned for the mutual interconversion of endo- into exo-80-8-d (122) (i) a conformational ring inversion passing through a planar classical cyclooctatrienyl cation, (ii) a walk rearrangement of the bicyclo[5.1.0] octadienyl cation formed as an intermediate, proceeding with retention at the migrating carbon atom C-8 (sr process) as postulated for an orbital symmetry controlled process (4). 

In the absence of a 2-electron donor, such as the double bond in 64 or the L in 58, bis-ir-aWyl nickel complexes are found with the 7r-allyl groups in nearly parallel planes and trans to each other (tail-to-tail), as shown by the X-ray structures of (i7 -2MeC3H4)2Ni (66) and (i7 -cyclooctatrienyl)2Ni/ In toluene-rfg solution (i7 -C3H6)2Ni and (r/ -... 

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