We are currently involved in two related projects: the study of gamma-silyl carbocations destabilized by alpha-trifluoromethyl groups, and the application of gamma-silyl bridging toward the synthesis of strained hydrocarbon systems.
Secondary carbocations containing a gamma-silyl substitutent are known to be stabilized by a bridging, or "percaudal" interaction in which the back-lobe of the silicon-carbon bond overlaps with the developing carbocation p-orbital. Subsequent elimination (one possible pathway) of the silyl substituent leads to formation of cyclopropanes. In a similar fashion, we have found that tertiary carbocations destabilized by a highly-electronegative alpha-trifluoromethyl group also exhibit strong percaudal participation, leading to formation of trifluoromethyl substituted cyclopropanes. In order to complete the mechanistic picture, we are currently synthesizing some deuterium-labeled analogs to study isotope effects. As part of the synthetic process, we are also investigating possible new methods for the oxidation of trifluoromethyl alcohols.
Our other project involves the use of a silyl-bridged system and subsequent silyl elimination from 3-trimethylsilylcyclobutyl systems to form bicyclbutane and/or trifluoromethylbicyclobutane. If successful, this novel approach may provide a model system for synthesis of more strained systems such as tetrahedrane. Strained hydrocarbon systems have potential applications as high-energy-density materials/fuels.