‘(η6-arene)Ru(bis-NHC)’ complexes for the reduction of CO2 to formate with hydrogen and by transfer hydrogenation with iPrOH

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Abstract
A series of bis-NHC-complexes of Ru and Ir have been tested in the reduction of carbon dioxide to formate. The use of one of the ‘(η6-arene)Ru(bis-NHC)’ complexes (labeled as 1 in the text) in the reduction of carbon dioxide with hydrogen affords a maximum TON value of 23000 at 200 °C. The same complexes were used in the reduction of carbon dioxide with iPrOH by the transfer hydrogenation methodology. For this reaction, a maximum TON value of 874 was achieved, the highest reported to date for this type of process. The activity of the catalyst is highly dependent on its stability because the complex has to stand the severe reaction conditions used in the process (200 °C).