Nickel Fluorocarbene Metathesis with Fluoroalkenes

Abstract

Alkene metathesis with directly fluorinated alkenes is challenging, limiting its application in the burgeoning field of fluoro-organic chemistry. A new nickel tris(phosphite) fluoro(trifluoromethyl)carbene complex ([P₃ Ni]=CFCF₃ ) reacts with CF₂ =CF₂ (TFE) or CF₂ =CH₂ (VDF) to yield both metallacyclobutane and perfluorocarbene metathesis products, [P₃ Ni]=CF₂ and CR₂ =CFCF₃ (R=F, H). The reaction of [P₃ Ni]=CFCF₃ with trifluoroethylene also yields metathesis products, [P₃ Ni]=CF₂ and cis/trans-CFCF₃ =CFH. However, unlike reactions with TFE and VDF, this reaction forms metallacyclopropanes and fluoronickel alkenyl species, resulting presumably from instability of the expected metallacyclobutanes. DFT calculations and experimental evidence established that the observed metallacyclobutanes are not intermediates in the formation of the observed metathesis products, thus highlighting a novel variant of the Chauvin mechanism enabled by the disparate four-coordinate transition states.

Keywords: Chauvin mechanism; alkene metathesis; fluoroalkenes; metallacyclobutanes; nickel carbenes.