Synthesis of half-sandwich ruthenium(II) and iridium(III) complexes containing imidazole-based phosphinite ligands and their use in catalytic transfer hydrogenation of acetophenone with isopropanol

Two ionic liquids (3-(3-chloro-2-hydroxypropyl)-1-vinyl-1H-imidazol-3-ium chloride and 3-(3-chloro-2-hydroxypropyl)-1-butyl-1H-imidazol-3-ium chloride) were prepared from commercially available, inexpensive 1-vinyl imidazole or 1-butyl imidazole, respectively, in ethanol at room temperature. Then, these ionic liquids were treated with PPh2Cl to obtain ionic liquid-based phosphinite ligands and the reaction of these phosphinites with [Ru(& eta;6-benzene)(& mu;-Cl)Cl]2, [Ru(& eta;6 p-cymene)(& mu;-Cl)Cl]2, or [Ir(& eta;5-C5Me5)(& mu;-Cl)Cl]2 gave the corresponding ruthenium and iridium complexes. Structures of the synthesized compounds were clarified by multinuclear NMR and IR spectroscopy as well as microanalysis. Furthermore, the complexes were applied as catalysts in the transfer hydrogenation of acetophenone derivatives to afford the corresponding alcohols with high conversions. Notably, [Ru(Ph2PO-C8H11N2Cl2)(& eta;6-benzene)Cl2] acts as a good catalyst, giving the corresponding alcohols in 97-98% yields in 15 min at 82 degrees C (TOF & LE; 400 h-1) for the transfer hydrogenation reaction in comparison to analogous complexes. The catalysts are also useful for a variety of related ketone substrates with various elec-tronic and steric regulating groups.