N-Heterocyclic Olefin Stabilized Borenium Cations

The reaction of the N-heterocyclic dicarbene (NHDC) [:C{[N(2,6-Pri2C6H3)]2CHCLi(THF)}]nwith iodomethane, in a hexane/THF mixture, affords the ylidic N-heterocyclic olefin NHCCH2(1; NHC = :C{N(2,6-Pri2C6H3)CH}2) in high yield. The reaction of 1with BBr3in hexane gives the neutral compound NHC–CH2:BBr3(2), which in THF unexpectedly converts to the borenium salt [NHC–CH2:B{O(CH2)4Br}2]+[Br]−(3) through ring opening of THF.