Recently, we have investigated the interconversion between CO2/H2 and formic acid by hydrogenation of CO2 and dehydrogenation of formic acid using metal catalysts with 2,2'-bipyridine (bpy) derivative ligands in water without organic additives.1,2,3 Herein, we report the highly efficient dehydrogenation of formic acid in water with simple azole containing complexes.4The newly designed iridium complexes with azole ligands exhibit higher catalytic activities than the unsubstituted bpy analogues [Cp*Ir(bpy)X]n+ in the dehydrogenation of formic acid in aqueous solutions. In particular, the iridium complex with tetramethyl biimidazole ligand achieved a TOF value as high as 34,000 h-1 (80 �C) which is higher than TOF values of any other mononuclear complexes yet reported. Nevertheless, the azole complexes is more robust in concentrated aqueous solutions of formic acid. The remarkable activity and stability are strongly affected by the imidazole structure and electron donating methyl groups.(1) Hull, J. F.; Himeda, Y.; Wang, W.-H.; Hashiguchi, B.; Periana, R.; Szalda, D. J.; Muckerman, J. T.; Fujita, E. Nat. Chem. 2012 , 4, 383.(2) Himeda, Y. Green Chem. 2009 , 11, 2018.(3) Himeda, Y.; Miyazawa, S.; Hirose, T. ChemSusChem 2011 , 4, 487.(4) Manaka, Y.; Wang, W.-H.; Suna, Y.; Kambayashi, H.; Fujita, E.; Muckerman, J. T.; Himeda, Y. Catalysis Science & Technology 2013 . 10.1039/C3CY00830D.

Hydrogen evolution by dehydrogenation of formic acid using iridium catalysts with azole ligands

247th National Meeting (2014)

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