X PhD-Chem Day
Pisa, April 23, 2013
Synthesis of novel dicarbene iridium(III) complexes as catalysts for
water oxidation
Andrea Volpe, Cristina Tubaro*, Marino Basato
Dipartimento di Scienze Chimiche, Università degli Studi di Padova, via Marzolo 1, 35131, Padova
The increasing global energy consumption has stimulated the research of sources alternative to
fossil fuels.[1a] An attracting and environmental friendly opportunity is represented by the catalytic
splitting of water into the highly energetic H2 and O2 molecules.[1] In this contribution the attention
is focused on the oxidative half reaction, which is not only endoergonic but also rather slow and
mechanistically complex.[2] Indeed, the reaction requires the loss of 4 protons and 4 electrons in a
multistep process (2H2O  O2 + 4H+ + 4e-). As well known good catalytic systems are based on
IrO2 nanoparticles, but a fine modulation of their properties is difficult, so the use of molecular
iridium complexes is preferred taking advantage of the possibility of tuning their stereo-electronic
characteristics by a proper choice of the coordination set.[3, 4]
In our lab we have prepared a series of new iridium complexes with different N-heterocyclic
dicarbene ligands that can afford both mononuclear and dinuclear species, depending on the nature
of the linker between the carbene units. Some of the synthesized complexes have been tested as
catalysts for water oxidation in presence of cerium(IV) or periodate as sacrificial oxidant.
Finally preliminary results on the photoactivated cycle in the presence of [Ru(bpy)3]2+ (bpy = 2,2’bipyridine) as the photosensitizer and sodium persulfate (Na 2S2O8) as the sacrificial electron
acceptor will be reported.
References
[1] (a) N. S. Lewis, D. G. Nocera, Proc. Natl. Acad. Sci. U.S.A., 2006, 103, 15729; (b) E. A. Karlsson, B. L. Lee, T.
Åkermark, E. V. Johnston, M. D. Kärkäs, J. Sun, Ö. Hansson, J. E. Bäckvall, B. Åkermark, Angew. Chem. Int. Ed.,
2011, 50, 1; (c) N. Armaroli, V. Balzani, ChemSusChem, 2011, 4, 21.
[2] (a) P. G. Hoertz, T. E Mallouk, Inorg. Chem., 2005, 44, 6828; (b) K. J. Young, L. A. Martini, R. L. Milot, R. C.
Snoeberger III, V. S. Batista, C. A. Schmuttenmaer, R. H. Crabtree, G. W. Brudvig, Coord. Chem. Rev., 2012, 256,
2503.
[3] J. Kiwi, M. Grätzel, J. Am. Chem. Soc., 1979, 101, 7214.
[4] (a) N. D. McDaniel, F. J. Coughlin, L. L. Tinker, S. Bernhard, J. Am., Chem. Soc., 2008, 130, 210; (b) R.
Lalrempuia, N. D. McDaniel, H. Muller-Bunz, S. Bernhard, M. Albrecht, Angew. Chem. Int. Ed. 2010, 49, 9765; (c) J.
F. Hull, D. Balcells, J. D. Blakemore, C. D. Incarvito, O. Eisentstein, G. W. Brudvig, R. H. Crabtree, J. Am. Chem.
Soc., 2009, 131, 8730; (d) A. Bucci, A. Savini, L. Rocchigiani, C. Zuccaccia, S. Rizzato, A. Albinati, A. Llobet, A.
Macchioni, Organometallics, 2012, 31, 8071.
*Corresponding author: Cristina Tubaro Tel: +39 049 8275655; fax: +39 049 8275223;
e-mail address: [email protected]