Cyclooctatetraene, dianion preparation

The 1.4-dihydro-l,4-diazocines prepared from iyn-benzene diimines (Section 1.4.1.2.) can be transformed to other derivatives by exchange of the substituents at nitrogen. For this purpose, the dipotassium salt of 1,4-diazocine is generated and then reacted with appropriate electrophiles. For example, reduction of the bistosyl derivative 3 gives a relatively stable dianion, a lOrr-electron system analogous to cyclooctatetraene dianion, which on protonation clearly gives the parent l,4-dihydro-l,4-diazocine (4, E = H) as the only product. 

By use of a similar method other more stable 1-substituted phosphiranes are prepared, 1-phenylphosphirane (123) being the most stable. When the cyclooctatetraene dianion is treated with dichlorophenylphosphine the bicyclic 1-phenylphosphirane derivative (124) is formed. At 70 °C in CHC13 it rearranges into the bicyclic phosphabicyclo[4.2.1]heptane derivative (125). Oxidation and photochemical reaction give the tricyclic phospholene 1-oxide derivative (126 equation (76)) (66JA3832). 

Another example concerns the initial electronic reduction of a-nitrostilbene (Todres, Dyusengaliev, Ustynyuck 1982 Todres, Dyusengaliev, Sevast yanov 1985 Todres Tsvetkova 1987 Charoenkwan and others, in preparation). The reduction develops as in process (a) in Scheme 2-7 if the mercury cathode as well as the cyclooctatetraene dianion are electron sources, and as in process (b) if the same stilbene enters the charge-transfer complexes with bis(pyridine)-tungsten tetra(carbonyl) or uranocene. For (b), the charge-transfer bands in the electronic spectra are fixed. So the mentioned data reveal a great difference in electrochemical and chemical reduction processes (a) and (b). 

The cyclooctatetraene dianion has a planar, regular octagonal structure with C — C bond lengths of 1.40 A close to the 1.397 A bond lengths in benzene. Cyclooctatetraene itself has eight pi electrons, so the dianion has ten (41V+2), with N = 2. The cyclooctatetraene dianion is easily prepared because it is aromatic. 

Benzannelated cyclooctatetraene (COT) has attracted much interest due to the variability of isomers of the dibenzannelated COT and the possibility to prepare doubly and quadruply charged systems. Dibenzo[a,d]cyclooctatetraene dianion (392 ) was prepared in 1965 127). The H NMR spectrum of 392- was studied and compared with its isomer i.e. dibenzo[a,e]cyclooctatetraene dianion (402 ). The two dianions were prepared by potassium metal reduction of 39 and 40, respectively 128,129). These... 

In a series of publications, Stevenson et al. have demonstrated that the enthalpies of generation of polyacene dianions can be obtained by calorimetric measurements. Compared to their calculated instability in the gas-phase 70), THF solutions of polycyclic dianions are thermodynamically and kinetically stable as evidenced by their spontaneous formation and persistence. The solvation energy of the dianions plus that of two cations must overcome the repulsive interaction of the charges. This aspect has been demonstrated by Stevenson in his studies on the cyclooctatetraene dianion 70). The dianion sodium salts were prepared in THF in thin-walled glass bulbs and the bulbs were crushed under water in a calorimeter system. The heat of aquation of the solvent is taken into account and thus, the net change in the heat content of the calorimeter vs. the millimoles of dianion salt is obtained. The plots are linear and the slopes represent the enthalpies of the following reaction (Eq. 20) ... 

Few 1 -benzothiophene-S-oxides 218 were obtained in moderate yields by treatment of 1-arylacetylenes 219 with sulfur dioxide and benzene in the presence of antimony pentafluoride250 (equation 127). A series of cyclic sulphoxides have been prepared by hydrolysis of the corresponding alkoxy sulphonium salts 220251-254 (equation 128). Syn-sulphoxide 221 was obtained in a low yield (15-20%) in the reaction of the dianion of cyclooctatetraene 222 with thionyl chloride255 (equation 129). 

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 cyclooctatetraenyl dianion 19 (COT-2) is an aromatic 10a electron system and hence can be readily prepared from cyclooctatetraene by reduction (alkali metals or electrochemically). An early report [36] of the photochemistry of COT-2 in the presence of weak acids such as amines and terminal alkynes showed that it is protonated in the excited state (to give the monoanion) COT-2 is more basic in the excited state than in the ground state. However, in the absence of such weak acids, photolysis of COT-2 results in electron photoejection [37-39]. The electron photoejection process and subsequent chemistry has been studied in... 

In order to study a bis[8]annulene compound with a divalent central metal atom we have synthesized and characterized the divalent ytterbium complex K2[Yb(CgHg)2]F K2[Yb(CgHg)2]r and its calcium analogue, K2[Ca(CgHg)2].51 These compounds were prepared by a reaction which utilizes the solubility of ytterbium and calcium metals in liquid ammonia. Reaction of cyclooctatetraene, potassium and either ytterbium or calcium, in liquid ammonia solution, gives the desired potassium salt of the complex dianion. 

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