Group 9 complexes of an N-heterocycle carbene bearing a pentafluorobenzyl substituent: attempted dehydrofluorinative coupling of cyclopentadienyl and N-heterocycle carbene ligands

Treatment of N-methylimidazole with pentafluorobenzyl bromide produces 1-pentafluorobenzyl-3-methylimidazolium bromide (1), which reacts with silver(I) oxide to give the N-heterocycle carbene (NHC) complex 1-pentafluorobenzyl-3-methylimidazolin-2-ylidene silver(I) bromide (2). Complex 2 acts as a carbene transfer reagent giving the complexes [(η⁵-C₅Me₅)MCl₂(NHC)] (3a, M = Rh; 3b M = Ir) on reaction with [(η⁵-C₅Me₅)MCl(μ-Cl)]₂. An attempt to use intramolecular dehydrofluorinative coupling methodology to link the carbene and the pentamethylcyclopentadienyl ligands of [(η⁵-C₅Me₅)RhCl(CN^tBu)(NHC)]BF₄ was unsuccessful.