Lithium-containing crown ether complexes

Discrete diarylcuprate anions have been observed in crystals in which the lithium cation is complexed by crown ethers.5 Both tetrahedral Ph4Cu4 and [Ph2Cu] units have been observed in complex cuprates containing (CH3)2S as a ligand. [Ph3Cu]2- units have also been observed as parts of larger aggregates.6... 

CpLi exists in ethers as a contact ion pair, in which the lithium ion is located above the cyclopentadienyl ring. The crystal stmcture of CpLi(12-crown-4) reveals analogous stmctural features. This complex has a sandwich-type stmctnre in which the lithium ion is coordinated to the fonr oxygen atoms of the crown ether on one side and to the Cp ring on the other. Several X-ray stmctnres of alkah metal cyclopentadienyl compounds containing silyl snbstitntion of the Cp ligand have been reported. The stmctnres of fluorenyl alkali metal complexes (Li-Cs) stabilized by diglyme have also been reported. The crown-ether-stabUized compounds of cyclopentadienyl, indenyl, and flnorenyl with the heavier metals, Rb and Cs, have also been reported. A common stmctural feature is the if coordination of... 

Both the carbanion and carbocations are stable provided they contain [An+ 2) K electrons. For example, cyclopentadienyl anion, cyclopropenium cation, and tropyhum cation exhibit unusual stability. Stable carbanions do, however, exist. In 1984 Ohnstead presented the lithium crown ether salt of the diphenylmethyl carbanion from diphenylmethane, butyllithium, and 12-crown-4 at low temperatures. Addition of n-butyUithium to triphenyhnethane in THF at low temperatures followed by 12-crown-4 resulted in a red solution and the salt complex precipitated at —20°C. The central C-C bond lengths are 145 pm with the phenyl ring propelled at an average angle of 31.2° (Scheme 3.11). 

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