Deaggregation of Trimethylsilylmethyllithium

Polyamine donor bases such as N,N,N′,N′‐tetramethylethylenediamine (TMEDA), (–)‐sparteine and N,N,N′,N″,N″‐pentamethyldiethylentriamine (PMDETA) have been employed to deaggregate parent trimethylsilylmethyllithium (1). The crystal structures of the dimers [(TMEDA)·LiCH2SiMe3]2 (2) and [{(–)‐sparteine}·LiCH2SiMe3]2 (3) were determined and reveal a four‐membered ring as the central structural motif. The two lithium atoms are each coordinated by the chelating ligands and the carbanions. The Li–C contacts show alternating bond lengths. The monomer [(PMDETA)·LiCH2SiMe3] (4) has the shortest Li–C contact of the aggregates discussed, and the Me3Si group points toward the central nitrogen atom of the PMDETA ligand, even if this alignment seems unfavourable for steric reasons. The bond lengths and angles of compounds 2–4 are discussed in relation to the orientation of the lone pair at the carbanion. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)