General Access to Acenaphthene-FusedN-Heterocyclic Carbene Ligands

We communicate a general method for the syntheses of acenaphthene-fused imidazolinium salts that are direct precursors to augmented N-heterocyclic carbenes with a fixed cis geometry. Reduction of bis(imino)acenaphthene ligands with a LiAlH4/AlCl3 reagent mix initially produced the corresponding 1,2-diamines which, upon ring-closing reaction with triethyl orthoformate in acidic solution, gave the requisite ionic intermediates. Formation of the carbenes was then shown by preparation of selected [Cu(NHC)] complexes that were obtained via treatment of the respective imidazolinium salt with base in the presence of a Cu(I) source.