Silicium dioxide is one of the most abundant and well-studied compounds on earth. The chemistry of SiO₂ in its molecular form and other simple silicon oxides, however, is essentially unknown. This is due to their highly reactive Si=O bonds and their tendency towards oligomerization.

Gregory H. Robinson, University of Georgia, Athens, USA, and co-workers have succeeded in stabilizing Si₂O₃ and Si₂O₄ with bulky N-heterocyclic carbene ligands (NHCs). Starting from the stabilized disilicon coumpound NHC^Dipp–Si=Si–NHC^Dipp (Dipp = diisopropylphenyl), oxidization with N₂O resulted in NHC^Dipp–Si₂O₃–NHC^Dipp. Reaction of the same complex with O₂ gave NHC^Dipp–Si₂O₄–NHC^Dipp (pictured) as a product.

The researchers have characterized the compounds by ¹H and ²⁹Si NMR spectroscopy as well as X-ray crystallography. The bonding situation was investigated with quantum chemical calculations, which showed zwitterionic resonance structures as the major contributors and only a minor double bond character of the terminal Si–O bonds. Using bulky NHC ligands as steric “shields” thus allows the stabilization of elusive main-group oxides that would otherwise oligomerize.

• Stabilization of elusive silicon oxides,
  Yuzhong Wang, Mingwei Chen, Yaoming Xie, Pingrong Wei, Henry F. Schaefer, Paul von R. Schleyer, Gregory H. Robinson,
  Nat. Chem. 2015.
  DOI: 10.1038/nchem.2234