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.