Phenyllithium-diethyl ether tetrameric complex

An interesting mixed tetrameric complex containing three equivalents of phenyllithium and one equiv-alent of lithium bromide, i.e. [(PhLi)3-LiBr3Et20], depicted as (116), has been characterized." In this mixed aggregate the lithium atom diagonally opposite Ae bromide in the tetramer rem s unsolvated by an ether molecule. Recall that the cyclopropyllithium lithium bromide-diethyl ether complex (44) with... 

Phenyllithium is known to form, in equilibrium with the monomer, a dimer 25 (Scheme 1-21) held together by electron-deficient partial bonds. However, phenyllithium can also adopt the structure of a lithium lithiate ion pair 26 (Scheme 1-21). What makes the difference The solvent plays a capital role. As long as the solvation forces remain moderate as in diethyl ether, the doubly carbon-lithium-carbon bridged dimer 25 is energetically most favorable. In a 2 1 mixture of cylohexane and diethyl ether, phenyllithium even assembles a tetrameric cluster. " " in neat THF, the four-centered dimer 25 is found in equilibrium with the monomer. " However, in the presence of the powerful electron-donor hexamethylphosphoric triamide (HMPA), it is the ion pair 26 that coexists with the monomer. Analogous lithiate complexes have been identified with... 

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