Influence of Amino Functions on the Coordination Ability of Silyl Ethers and Disiloxanes

Amino-functionalized silyl ethers and siloxanes are a synthetically highly valuable class of compounds. The Si–N bond was studied with regard to its possible electronic influence on Si–O bonds in silyl ethers and disiloxanes. A thermochemical investigation of the deaggregation of a tBuLi tetramer using a variably patterned ligand collection was carried out by means of density functional theory calculations. These results built the basis for an in-depth natural bond orbital analysis of the ligands and the respective [ligand·tBuLi] complexes. The molecular model system was chosen in such a way that structural influences were largely excluded and the focus could be placed on the difficult electronic structure. In the presence of an additional silicon–nitrogen bond, a slightly increased coordination ability of the Si–O–C/Si–O–Si unit was found for both silyl ethers and disiloxanes. It appears that the decrease of the hyperconjugative oxygen lone electron pair stabilization upon coordination to lithium is balanced by an increase of the nitrogen lone electron pair hyperconjugation, especially in the disiloxane complexes. In order to understand the thermochemical differences between silyl ether (Si–O–C) and ether (C–O–C) units when coordinating to the lithium center, the interplay of covalent and ionic contributions for the O–Li interactions must be taken into account, with the latter dominating in the silicon-based species.