Highly Electron-Deficient Carbon, Boron and Silicon Compounds

With support from the Chemical Synthesis Program of the Chemistry Division, Professor Guy Bertrand of the Department of Chemistry and Biochemistry at the University of California – San Diego, is studying highly electron-deficient carbon, boron and silicon compounds. Usually atoms such as carbon, boron, and silicon contain a full octet, i.e. are surrounded by eight electrons when they form compounds with other atoms. This project seeks to isolate species that only possess 4 or 5 surrounding electrons. The isolation such compounds has been impeded by the belief that they are inherently unstable. However, by attaching groups that are specially designed to stabilize electron deficiencies stable compounds with these very low electron counts will be prepared. The availability of these stable versions provides a better understanding of chemical reaction mechanisms and opens the way for new applications. As an example, carbon compounds with six-valence electrons have become powerful tools in chemistry and have found medicinal and material science applications. This project will prepare carbon, silicon and boron with as few as four valence electrons. Although the work is fundamental in nature, the resulting species will certainly find a plethora of applications and benefit society at large. The laboratory of the PI is a joint venture between UCSD and the French CNRS. It serves to promote the exchange of undergraduates and graduates between UCSD and European Universities. The recent isolation of a monsubstituted carbene, namely an aminocarbene (R2NCH), demonstrates that an amino substituent can tame the intrinsic instability of a six-electron species. Therefore, the Bertrand team believes that using this principle compounds featuring a main-group element with only five- and even four-valence electrons can be isolated. Monocoordinated carbon compounds, namely amino carbynes (R2NC:●) and amino carbocations (R2NC:+), as well as the isoelectronic borylene radical anions (R2NB:●-) and borylenes (R2NB:) will be prepared. Apart from monocoordinate systems, dicoordinate carbon radical cations (R2C+●) and carbodications (R2C++), which also feature only five and four valence-electrons around the carbon atom and are the one and two electron oxidized forms of a carbene, respectively, are also being targeted. Once these electron-deficient species are in hand, their synthetic utility will be explored. As an illustration, carbodications R2C++ could find applications as strong Lewis acids, including in frustrated Lewis pair chemistry. This project which is at the nexus of physical, organic, inorganic and organometallic chemistry is well suited to the education of chemists at all levels. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.