Small and Prototypic: Dimethyl Ether in Lithiumorganics─Insights from Experimental Charge Density Studies

Dimethyl ether (DME) is widely used in calculations as a model ligand due to its structural simplicity. In contrast, its application in structural chemistry is limited. Here, we present the first crystal structures of standard lithiumorganics with this simplest gaseous ether to provide an experimental basis for calculated geometries. The aggregation sizes are comparable to those with tetrahydrofuran, showing that DME can replace this ligand without changing the geometrics drastically. The solid-state structure of tert-BuLi·3DME is particularly interesting, representing the first lithiumorganic high-resolution structure with only etheric ligands. To put the compound into context, a high-resolution structure of monomeric LiI·3DME was obtained, and experimental charge density studies for both compounds were carried out, raising new insights into bond situations. The density at the Li-C bond contains more shared density than Li-I, which is much more on the closed shell interaction side. The shorter Li-O distances in LiI·3DME witness that the halide provides less density to the metal than the carbanion. This deficiency is counterbalanced by the more closely coordinated DME donors. These results establish DME as a unique rigid ligand, enabling access to high-quality crystal structures that provide experimental insights into the bonding properties of lithiumorganic compounds.