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Silicon dioxide as a molecular reagent

Researchers isolate monomeric SiO2 in a complex for the first time, finally creating a way to incorporate the unit in organic synthesis

by Stephen K. Ritter
March 20, 2017 | A version of this story appeared in Volume 95, Issue 12

Carbon dioxide is a ubiquitous stable gaseous molecule with O=C=O bonding. Yet in one of the quirks of the periodic table, silicon dioxide—the next heaviest group 14 dioxide—is remarkably unstable as a monomeric species. There’s plenty of SiO2 around, but it forms network structures, for example in sand, held together by Si–O single bonds. Chemists have looked for the means to create molecules containing individual O=Si=O units and have come close with SiO and SiO, but until now the seemingly simple species has remained elusive.Antoine Baceiredo and Tsuyoshi Kato of the University of Toulouse and their colleagues finally solved this challenge by finding the right combination of stabilizing ligands to get the job done (Angew. Chem. Int. Ed. 2017, DOI: 10.1002/anie.201611851). The researchers previously created several main-group complexes containing Si=O, O–Si=O, or O=Si-OH units supported by electron-donating and/or electron-accepting ligands. Ultimately they found that pairing an amine-substituted pyridine donor ligand and an iminophosphorane-based donor-acceptor ligand creates a stable environment for SiO2. The new complex is soluble in organic solvents and is a stable solid at room temperature. But most interesting, the researchers say, is that the complex can be used as an SiO2-transfer reagent. In an initial test, they show that the complex reacts with phenylsilane to produce a trisiloxane. The team is continuing to explore the reaction chemistry of the new complex, including its ability to produce chiral SiO2-containing molecules.


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