TMEDA organolithium reagents

Organolithium reagents (RLi) are tremendously important reagents in organic chemistry. In recent years, a great deal has been learned about their structure in both the solid state and in solution. X-ray analysis of complexes of n-butyllithium with A,A,A, A -tetramethylethylenediamine (TMEDA), THF, and 1,2-dimethoxyethane (DME) shows them to be dimers and tetramers [e.g., (BuLi DME)4]. X-ray analysis of isopropyllithium shows it to be a hexamer. 

Our interest in the synthetic utility of N-chelated organolithium compounds was prompted by this early work. Since detailed experimental procedures were not generally available at that time, we initiated a study of the effects of time, temperature, stoichiometry, etc., on the reactions of BuLi-TMEDA with benzene. We found that optimum metalation of benzene occurs when the preformed BuLi-TEMEDA complex, prepared from equimolar amounts of the organolithium reagent and diamine, is... 

The reactivity of the organolithium compounds is increased by adding molecules capable of solvating the lithium cations. Tetramethylenediamine (TMEDA) is commonly used for organolithium reagents. This tertiary diamine can chelate lithium. The resulting complexes generally are able to effect deprotonation at accelerated rates.In the case of phenyllithium, NMR studies show that the compound is tetrameric in 1 2 ether-cyclohexane, but dimeric in 1 9 TMEDA-cyclohexane. ... 

Organolithium reagents are oligomers (i.e., dimers, trimers, and higher species) in nondonor solvents such as alkanes LiMe is a tetramer with a cubane structure 14.1, for example. RLi forms solvates with THE Addition of the chelating ligand Me2NCH2CH2NMe2 (TMEDA) leads to formation of a monomer, and this increases the reactivity. n-BuLi can deprotonate toluene... 

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