Preparation and Functionalization of a Range of Main-Group Trifluoropropynyl Organometallic Compounds:  The Application of Metalloid-Directed Carbolithiation to the Selective Synthesis of Novel Fluorocarbon Fragments

The reaction of 1,1,1,3,3-pentafluoropropane (CF3CH2CF2H, HFC-245fa) with 3 equiv of n-butyllithium at −10 °C leads to the generation of trifluoropropynyllithium in excellent yields. This reagent reacts readily with a range of group 14 electrophiles R4 - n EX n (R = Ph, Et; E = C, Si, Ge, Sn, Pb; X = Cl, Br) to yield the organometalloid trifluoropropynyl compounds R4 - n E(C⋮CCF3) n . Three of these compounds, Ph3EC⋮CCF3 (E = C, Si, Ge), have been crystallographically characterized, representing the first such study of these materials. The silane Ph3SiC⋮CCF3 has been derivatized by reaction with LiAlH4 and a range of organolithium reagents (RLi, R = n-Bu, Ph, t-Bu) to afford a new series of β-CF3-substituted vinylsilanes of the type Ph3SiCHC(CF3)R, with predominantly E geometry at the double bond. In the cases R = n-Bu, t-Bu, and Ph, these materials have been crystallographically characterized. Additionally, a remarkably facile cyclization pathway for Ph3SiC⋮CCF3, initiated by t-BuLi, that yields the respective gem-difluorocyclopropene has been explored and is described in detail, along with its extension to a number of other systems.