Synthesis and structure of the tmeda adduct of a dibenzyl lithiate anion containing four-coordinate lithium

Mesitylene may be lithiated almost quantitatively by Lin-Bu in a large excess of tmeda, resulting in the formation of the solvent-separated ion pairs [Li(tmeda)2](+)[(tmeda)Li(CH2C6H3-3,5-Me-2)(2)](-) (1) (tmeda = N,N,N ' ,N ' -tetramethylethylenediamine), the anion of which is a lithiate containing lithium bound to two eta (1)-coordinated benzyl groups and one molecule of tmeda, resulting in the coordination number 4 at lithium in a distorted tetrahedral coordination geometry. Compound I is the first four-coordinate diorgano lithiate. Likewise, benzyl lithiates have no precedent in the rich structural chemistry of benzyllithium compounds.