Transition-Metal-Free Formation of C-E Bonds (E = C, N, O, S) and Formation of C-M Bonds (M = Mn, Mo) from N-Heterocyclic Carbene Mediated Fluoroalkene C-F Bond Activation.

Abstract

Herein, a recently reported polyfluoroalkenyl imidazolium salt is shown to react with nitrogen-, oxygen- and sulfur-based nucleophiles at the C β position in a stereoselective and regioselective fashion, without the use of a transition metal. In contrast, reactivity with 1-methylimidazole demonstrates net substitution at C α . This product reacts quantitatively with water, affording clean transformation of a difluoromethylene group to give an α,β-unsaturated trifluoromethyl ketone. Further reactivity studies demonstrate that the difluoromethyl fragment of an N-heterocyclic fluoroalkene is capable of direct C-C bond formation with NaCp through loss of sodium fluoride and double C-F bond activation (Cp = cyclopentadienide). TD-DFT calculations of this product indicate that both the HOMO and LUMO are of mixed π/π* character and are delocalized over the N-heterocyclic and Cp fragments, giving rise to a very intense absorption feature in the UV-vis spectrum. Additionally, two carbonylmetalate-substituted fluorovinyl imidazolium complexes featuring Mn and Mo were isolated and fully characterized.