Cyclooctatetraene, dianion spectrum

The species (CH)8Mg, or we should say its THF 2.5-solvate, is readily formed from cyclooctatetraene and Mg. The NMR spectrum shows eight equivalent ring atoms and so suggests either the cyclooctatetraene dianion and Mg salt or a putative (and highly fluxional) solvated magnesacyclopentene (or more properly magnesabicyclonon-atriene). However, there is no structural data for the rf open sandwich species and the enthalpy of formation of this simple and sensible half-sandwich, or tight ion pair, cannot even be estimated. 

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 analogy to the cyclooctatetraene dianion, 71 also forms a very stable sandwich complex 75 upon reaction with UC14 in THF (Scheme 18) [69]. The H NMR spectrum of this complex 75 revealed a very characteristic singlet at 6 = -21 ppm ( ) which is in good agreement with the chemical shift of urano-cene,the bis(cyclooctatetraenediyl)uranium complex [70]. 

The NMR spectrum indicates a planar aromatic structure. It has been demonstrated that the dianion is more stable than the radical anion formed by one-electron reduction, since the radical anion disproportionates to cyclooctatetraene and the dianion ... 

Addition of two electrons to cyclooctatetraene yields the dianion 45, which shows a single peak in the proton magnetic resonance spectrum.21 The conclusion... 

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