Planar Tetracoordinate Silicon in Organic Molecules As Carbenoid-Type Amphoteric Centers: A Computational Study

Designing and synthesizing a stable compound with a planar tetracoordinate silicon (ptSi) center is a challenging goal for chemists. Here, a series of potential aromatic ptSi compounds composed of four conjugated rings shared by a centrally embedded Si atom are theoretically designed and computationally verified. Both Born-Oppenheimer molecular dynamics (BOMD) simulations and potential energy surface scannings verify the high stability and likely existence of these compounds, particularly Si-16-5555 (SiN4C8H8) with 16 pi electrons, under standard ambient temperature and pressure. Notably, the Huckel aromaticity rule, which works well for single rings, is inconsistent with the high stability of Si-16-5555 where the 16 p electrons are spread over four five-membered rings fused together. Bonding analyses show that the strong electron donation from the peripheral 12-membered conjugated ring with 16 pi electrons to the vacant central atomic orbital Si 3p(z) leads to the stabilization for both the ptSi coordination and planar aromaticity. The partial occupation of Si 3p(z) results in the peculiar carbenoid-type behaviors for the amphoteric center. By modulating the electron density on the ring with substituent groups, we can regulate the nucleophilic and electrophilic properties of the central Si.

Automated summary

Designing and synthesizing stable compounds with planar tetracoordinate silicon (ptSi) centers is a challenging goal for chemists. A series of potential aromatic ptSi compounds, particularly Si-16-5555, have been theoretically designed and computationally verified for their high stability, with unique bonding and electronic properties. The research shows that the conventional aromaticity rule does not apply in this case, and the electron donation from peripheral conjugated rings plays a crucial role in stabilizing the compounds.