Synthesis of binuclear iridium(III) and rhodium(III) complexes bearing methylnaphthalene-linked N-heterocyclic carbenes, and application to intramolecular hydroamination

New methylnaphthalene-linked imidazolium salts 1 were synthesized through the reaction of 1,8-dibromomethylnaphthalene and N-alkylimidazole. On treatment of imidazolium salt 1 with silver oxide followed by [Cp∗MCl2]2 (M = Ir, Rh), binuclear iridium and rhodium complexes 2 were formed. Reaction of these complexes 2 with AgPF6 afforded Cl-bridged cationic binuclear iridium and rhodium complexes 3. X-ray crystallographic analysis of 3 revealed that the two imidazole rings of the carbene ligand are in a parallel geometry. The cationic binuclear iridium complexes 3-Ir could be applied to the intramolecular hydroamination reaction of 2-ethynylaniline to give the corresponding indole compound.