Structural influence of steric factors and donor functions on lithium silylamides in non-coordinating solvents.

We herein present the synthesis and crystallographic characterisation of lithium silylamides displaying different coordination numbers and aggregation states according to the number of N- and O-donor functions in the starting material, (aminomethyl) substituted silazane ligands. The dimeric dimethyl-(N-lithio-tert-butylamino)-piperidinomethyl)-silane and dimethyl-(N-lithio-iso-propylamino)-piperidinomethyl)-silane, with three-coordinate lithium centres, were prepared by deprotonation of the corresponding silazane with (n)BuLi. Using the tridentate silazane (1R,2R)-N(1)-[{(tert-butylamino)-dimethylsilyl}methyl]-N(1),N(2),N(2)-trimethylcyclohexane-1,2-diamine a mixed "dimer" of lithium silylamide and lithium silanolate with four-coordinate lithium centres was obtained. Additionally, a monomeric lithium silylamide was synthesised using the tridentate [bis(methoxyethyl)aminomethyl] side arm.