Reactivity of Ruthenium(II) Complexes Bearing Bis-NHC Ligands

Bis-imidazolium salts bearing N-2-fluorobenzyl substituents and methylene, ethylene, or propylene linkers ([H2-4]Br2–[H2-6]Br2) and the bis-imidazolium salt [H2-8]Br2 featuring an ethylene linker and N-3-fluorophenyl substituents have been prepared. Salts [H2-5]Br2 and [H2-6]Br2 react with [RuCl2(CO)2]n to give the bis-NHC chelate complexes [9] and [10]. Chloride substitution in [10] for the 2-nitrophenyl isocyanide ligand 11 yielded the complex [12]PF6. The nitro group of the isocyanide in [12]PF6 could not be reduced. Salts [H2-4]Br2 and [H2-5]Br2 yield with [RuCp*(MeCN)3]PF6 the chelate complexes [13]PF6 and [14]PF6, respectively. The propylene-bridged bis-imidazolium salt [H2-6]Br2 reacts with [RuCp*(MeCN)3]PF6 to give, via an oxidative addition of a C–H bond of the central methylene group of the linker, the seven-coordinate RuIV complex [15]PF6 bearing a tridentate CNHCCalkylCNHC ligand and a hydrido ligand. Introduction of a nitrophenyl isocyanide ligand to [14]PF6 and reduction of the nitro group to the primary amine was also possible. Finally, [H2-8]Br2 reacts with [RuCp*(MeCN)3]PF6 to give, after intramolecular oxidative addition of a Caryl–H bond followed by reductive elimination of an imidazolium group, the complex [20]PF6 bearing a unique tridentate CarylCNHCC═Cimidazolium chelate ligand.