Gas-phase synthesis of the silaisocyanoethylene molecule (C2H3NSi)

J Org Chem. 2012 Oct 5;77(19):8574-80. doi: 10.1021/jo3015402. Epub 2012 Sep 25.


The gas-phase reaction between the silicon nitride radical (SiN) and the prototypical olefin--ethylene--is investigated experimentally and theoretically for the first time. Silicon nitride (SiN) and the cyano radical (CN) are isoelectronic; however, their chemical reactivities and structures are drastically different from each other. Through the use of the cross molecular beam technique, we were able to study the notoriously refractory silicon nitride radical in reaction with ethylene under single-collision conditions. We investigated the similarities and also the distinct differences with the cyano radical-ethylene system. We find that the silicon nitride radical bonds by the nitrogen atom to the double bond of ethylene; in comparison, the cyano radical adds via its carbon atom. The silicon nitride addition is barrierless, forming a long-lived SiNCH(2)CH(2) collision complex, which is also able to isomerize via a hydrogen shift to the SiNCHCH(3) intermediate. Both isomers can emit a hydrogen atom via tight transition states to form the silaisocyanoethylene (SiNC(2)H(3)) molecule in an overall exoergic reaction. This presents the very first experiment in which the silaisocyanoethylene molecule--a member of the silaisocyanide family--has been formed via a directed synthesis under gas-phase single-collision conditions. In comparison with the isoelectronic cyano-ethylene system, the cyanoethylene (C(2)H(3)CN) isomer is formed. Therefore, the replacement of a single carbon atom by an isovalent silicon atom, i.e. shifting from the cyano (CN) to the silicon nitride (SiN) radical, has a dramatic influence not only on the reactivity with ethylene (carbon atom versus nitrogen atom addition) but also on the final reaction products. In the reactions of ethylene with silicon nitride and the cyano radical, the silaisonitrile over the silanitrile and the nitrile over the isonitrile reaction products are favored, respectively. This reaction provides rare experimental data for investigating the chemistry of bimolecular reactions of silicon nitride diatomics in chemical vapor deposition techniques and interstellar environments.