Cyclooctatetraene, COT

CyclooctatetraenylCompounds. Sandwich-type complexes of cyclooctatetraene (COT), CgH g, are well known. The chemistry of thorium—COT complexes is similar to that of its Cp analogues in steric number and electronic configurations. Thorocene [12702-09-9], COT2Th, (16), the simplest of the COT derivatives, has been prepared by the interaction of ThCl [10026-08-1] and two equivalents of K CgHg. Thorocene derivatives with alkyl-, sdyl-, and aryl-substituted COT ligands have also been described. These compounds are thermally stable, air-sensitive, and appear to have substantial ionic character. 

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

Connelly et al. (1979) investigated the reactions of arenediazonium salts with cyclooctatetraene (cot) and some of its transition metal compounds. Free cyclooc-... 

Cyclooctatetraene (COT) —> Semibullvalene (SB) Photorearrangement. Irradiation of COT yields semibullvalene [97], in spite of the fact that this photochemical reaction is forbidden by orbital conservation mles. The Longuet-Higgins loop for this system actually predicts that this should happen, although the reaction is phase preserving. (Fig. 42). This is another example of type C loop (Fig. 11). Only six of the eight electrons re-pair as COT transforms to SB. The reaction is made possible by the fact that COT valence isomerization, a phase-inverting reaction (four electron-pair Hiickel system), takes place simultaneously. One expects to produce in the reaction a COT isomer, that can be detected solely by proper substitution. 

Our success in super-stabilization of cation 6 led us to the preparation of a higher homologue, that is, cyclooctatetraene (COT), fully annelated with BCO units 9 (9). As compared with a large number of studies on its radical anion or dianions, the studies on the cationic species of COT have been quite limited. There have been only one study by Olah and Paquette on the substituted COT dication (70), which is a typical 6n Hiickel aromatic system, and few sporadic studies on radical cations, which involve indirect spectral observations, such as electronic spectra in Freon matrix at low temperature (77,72) and constant-flow ESR study (13). 

The most widely studied examples are cyclooctatetraene (COT, 1) and its derivatives. In such conventional aprotic solvents as DMF, dimethyl sulfoxid (DMSO), or acetonitrile containing tetraalkylammonium salts, two distinct one-electron reduction waves are observed at approximately —1.64 V and —1.80 V vs. saturated calomel electrode (SCE), with separations... 

Uranocene itself was prepared by allowing cyclooctatetraene (COT) to react with potassium in dry, oxygen-free tetrahydrofuran (THF) at —30° followed by the addition of a THF solution of anhydrous uranium tetrachloride ... 

In accord with the Hiickel rule of 4/t + 2 electrons, both cyciobutadiene and cyclooctatetraene (cot) are nonaromatic. Cyclooctatetraene contains alternating bond lengths and has a tub-shaped conformation ... 

Partially substituted derivatives of polyacetylene are synthesized via the ring-opening metathesis polymerization (ROMP) of cyclooctatetraene (COT) and its derivatives. Certain poly-COT derivatives afford soluble, highly conjugated poly acetylenes. These materials exhibit large third-order optical nonlinearities and low scattering losses. 

Benzene and cyclooctatetraene (COT) derivatives are formed by [2+2+2] and [2+2+2+2] cycloadditions of alkynes. At first the metallacyclopropene 107 and metallacyclopentadiene 108 are formed. Benzene and COT (106) are formed by reductive elimination of the metallacycloheptatriene 109 and the metallacyclononate-traene 110. Formation of benzene by the [2+2+2] cycloaddition of acetylene is catalysed by several transition metals. Synthesis of benzene derivatives from... 

The reduction of Zr(OR)4 compounds with Et2AlH in the presence of cyclooctatetraene (COT) produces the dihydride (COT)ZrH2. This reacts with protonic hydrogens, liberating hydrogen but since the dihydrides in general act as efficient hydrogenating catalysts for alkenes, the final hydrocarbon product formed is essentially a mixture of cyclo-octatriene and cyclooctadiene (110), e.g.,... 

You will probably be surprised to find cyclooctatetraene (COT for short), unlike benzene, is not planar. Also none of the double bonds are conjugated—there are indeed alternate double and single bonds in the structure but conj ugation is possible only if the p orbitals of the double bonds can overlap here they do not. Since there is no conjugation, there are two C-C bond lengths in cyclooctatetraene—146.2 and 133.4 pm—which are typical for single and double C-C bonds. If possible, make a model of cyclooctatetraene for yourself—you will find the compound naturally adopts the shape below. This shape is often called a tub . 

Cyclooctatetraene (COT). Tetrameriz atio 11 of acetylene to cydooctatetraene [629-20-9], C.H, although interesting, does not seem to have been used commercially. Nickel salts serve as catalysts. Other catalysts give benzene. The mechanism of tliis cyclotetramerization has been studied (4). 

The first tris(arene)niobinm complex, [Nb(l-4-J7 -anthracene)3], prepared by the Na or K anthracene rednction of NbCL (THF)2, undergoes facile anthracene displacement in the presence of CO to afford [K(18-crown-6)(THF)2][Nb(CO)6]. Rednction of TaCls by sodinm naphthalene provides [Na(THF)][Ta(j7 -naphthalene)3], the first homoleptic naphthalene complex of a third row transition metal. This complex reacts with CO and anthracene to give [Ta(CO)6] and [Ta(l-4-jj -anthracene)3], respectively. The latter prodnct reacts with cyclooctatetraene (COT) to give [Ta(COT)3]... 

One possible approach to the preparation of an all-hydrocarbon tripledecker compound, with the necessary 34-electron configuration, is to attempt to oxidize or reduce a near-miss complex (42), that is, one containing the correct number of ligands and metals but with an excess or deficiency of electrons. Two such attempts, involving complexes with bridging cyclooctatetraene (cot) ligands, have been reported. 

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