Chiral Transition-Metal Complexes of Phenanthro-Annulated N-Heterocyclic Carbenes - Synthesis and Reactivity

A straightforward route to chiral AgI and RuII complexes with phenanthrene-fused N-heterocyclic carbene (NHC) ligands is described. The chiral imidazole derivative 1 was prepared in high yield by a simple one-pot reaction starting from commercially available 9,10-phenanthrenequinone. Imidazolium salts 2 and 3 were obtained by alkylation of 1 with alkyl bromides and subsequent anion exchange with Amberlyst A21 resin. Deprotonation with KOtBu led to the corresponding free carbenes 4 and 5, which were isolated without dimerization. Stirring carbene 4 in acetonitrile resulted in CH insertion. AgI complexes were obtained by treatment of the imidazolium salts with Ag2O and showed an interesting low-temperature behavior in the 1H NMR spectrum. Transmetalation with a Ru precursor led to the corresponding RuII complexes.