Base-stabilized acyclic amino(ylidyl)silylenes: electron-rich donors for the stabilization of silicon-element multiple bonds

Abstract

Increasing the donor strength of Lewis bases is a viable strategy to stabilize reactive electron-deficient species. Herein, we utilize the strong electron-releasing power of ylide substituents to gain access to electron-rich silylenes. Based on the Roesky's amidinato chlorosilylene scaffold, we succeeded in isolating two amino(ylidyl)silylenes with a tosyl and cyano group in the ylide backbone, respectively. The tosyl system revealed to be amongst the most electron-rich silylenes known to date as measured by its Tolman electronic parameter. DFT studies showed that the ylide acts as a σ and π-donor, transferring electron-density into the empty p-orbital of the silicon center, thus resulting in its electron-richness and stability. The strong donor capacity of the silylene was used to stabilize further reactive silicon species: while treatment with carbon disulfide led to the formation of silylene-CS₂ complexes, the reaction with N₂O or CO₂ was found to depend on the electronic and steric properties of the ylide substituent. Whereas the tosyl system yielded a room-temperature stable silanone, the cyano-substituted silylene formed a carbonate complex with CO₂ and a dimeric silanone with N₂O. Additionally, both silylenes facilitated the isolation of silicon compounds with extended π-conjugated units, highlighting the potential of ylide substituents to stabilize unusual bonding situations.