η6-Hexahelicene Complexes of Iridium and Ruthenium: Running along the Helix

Abstract

The first η6-complexes of iridium and ruthenium coordinated to helicenes have been obtained. Hexahelicene (1), 2,15-dimethylhexahelicene (2), and 2,15-dibromohexahelicene (3) react with [Cp*IrCl2]2 and AgBF4 in CD3NO2 to afford quantitatively the complexes [Cp*Ir(η6-1)][BF4]2 (4A), [Cp*Ir(η6-2)][BF4]2 (5A), and [Cp*Ir(η6-3)][BF4]2 (6A), respectively. In all cases, the final thermodynamic products are similar, and they exhibit coordination between the 12 e– metal fragment [IrCp*]2+ and the terminal ring of the helicene. Monitoring the reaction by NMR shows formation of intermediates, some of which have been fully characterized in solution. These intermediates exhibit the metal fragment coordinated to the internal rings. We have also synthesized the bimetallic complex [(Cp*Ir)2(μ2-η6:η6-2)][BF4]4 (7), achieving coordination between two units [IrCp*]2+ and the helicene 2. Following an analogous methodology, we have prepared the complex [(η6-cymene)Ru(η6-2)][BF4]2 (8), which has been studied by X-ray diffraction, confirming the preferential binding to the terminal aromatic ring.