Silicon and Oxygen’s Bond of Affection: An Acyclic Three-Coordinate Silanone and Its Transformation to an Iminosiloxysilylene

A long-term dream comes true: An
acyclic, neutrally charged silanone
at last! Here, we report on the first examples of isolable acyclic,
neutral, three-coordinate silanones 2 with indefinite
stability as solids and lifetimes in solution of up to 2 days. The
electronic properties of the SiO bond were investigated via
DFT calculations and revealed the π-donating N-heterocyclic imino (NHI) and σ-donating silyl groups as key
factors for their enhanced stability. Besides initial reactivity studies
of 2 toward CO2 and methanol, different isomerization
pathways depending on the silyl substitution pattern were found. For 2a (R = TMS), a 1,3-silyl shift gave an intermediary disilene,
which was trapped as unique NHC-disilene adduct 6. For
the more stable silanone 2b (R = t-Bu),
a selective transformation to the first reported room temperature
stable, acyclic, two-coordinate N,O-silylene 7 exhibiting a fascinating siloxy ligand was
observed. Both compounds were fully characterized experimentally and
their bonding features were analyzed by theoretical calculations.