Neutral Magnesium Half-Sandwiches

Affixing an R group to the Mg of our half-sandwiches results in the second class of species, e.g. CpMgR. It is quite clear that the reaction in equation 22 

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. 

We note that both of the reactions (equations 23 and 24) (without additional solvating ligands explicitly being shown) proceed facilely . 

However, lacking thermochemical data on the other two butadiene and anthracene-related organomagnesia does not even allow us to deduce a bound for the enthalpy of formation of (CH)8Mg90. 

---