Communication
the use of an excess amount of the expensive [Ir(ppy)2(bpy)]+ upon examining the HER at equivalent quantities of the Ir pho-
photosensitizer is not optimal.
tosensitizer and the Co catalyst. The bis-cyclometalating ligand
gives a HOMO with both metal and ligand nature that is rela-
tively high in energy, while maintaining a low energy LUMO
owing to the terpyridine ligand in the role of ancillary ligand of
the IrIII complex. This shift in ligand composition in comparison
to phenylbipyridines allows greater control of the direction of
the MLLCT transition towards the Co catalyst and also allows
the HER to occur at lower energy than classic IrIII compounds.
The green-light LED centered at 525 nm covers the tail of
the [Ir(ppy)2(bpy)]+ absorption spectrum and overlays the [Ir-
Pyr-Co]+ band with appreciable molar absorptivity (see Figure 4
and Table 2). A molar absorptivity lower in the range of green
light than in the range of blue light results in a concomitant
decrease in hydrogen production; however, the tridentate sys-
tem has more sustained hydrogen evolution: TON of 113 for
[Ir-Py-Co]+ and
a TON of 12 for the reference system
CCDC 1419882 (for [Ir-Py-Co]+) contains the supplementary crystal-
[Ir(ppy)2(bpy)]+/[Co(dmgH)2PyCl] (Figure 5). Concerning rate of
activity, the overall decrease is remarkably different, as the ref-
erence system drops by over 4000 mmolH molPS–1 min–1 and
2
[Ir-Py-Co]+ decreases by only 30 mmolH molPS–1 min–1 and re-
2
Acknowledgments
mains homogeneous. For the bidentate model system, how-
ever, the rate does not decay as rapidly as it does for blue light.
Under yellow irradiation centered at 595 nm, [Ir-Py-Co]+ starts
The authors gratefully acknowledge the Fonds National pour la
Recherche Scientifique (F.R.S.-FNRS), Belgium, the Fonds pour la
Formation à la Recherche dans l'Industrie et dans l'Agriculture
(F.R.I.A.), Belgium, the Région Wallonne, Belgium, the Université
Catholique de Louvain, Belgium, and the Prix Pierre et Colette
Bauchau, Belgium for financial support. G. S. H. thanks the Natu-
ral Sciences and Engineering Research Council (NSERC), Canada
and the Direction des Affaires Internationales de l'Université de
Montréal, Canada for financial support. Prof. K. Van Hecke is
thanked for allowing access to his diffractometer.
a low production of hydrogen (TOF = 4 mmolH molPS–1 min–1)
2
after 5 h, and no activity is detected for [Ir(ppy)2(bpy)]+
(Table S5). The [Ir-Py-Co]+ system has low but sustainable activ-
ity from the start of the photoreaction until the end, which
suggests that tridentate systems are much more stable with IrIII
than with RuII.[21] The low quantum yield of [Ir-Py]+ could be
related to the fact that this photoinduced electron-transfer rate
is slower than that of [Ir(ppy)2(bpy)]+ (the low homogeneous
activity of the Ir–Co assembly could also characterize directional
electron transfer through the pyridylterpyridine to cobalox-
ime[19]). The pendant pyridine ring of [Ir-Py]+ could act as an
electron relay from the PS to the catalyst, as it links both enti-
ties[9d] and is the coordination site for cobaloxime. Coordination
of cobaloxime to the PS appears to be a crucial factor for the
efficiency and stability of the system.[9]
Keywords: Supramolecular chemistry · Photochemistry ·
Dihydrogen · Cobalt · Iridium
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Figure 5. Hydrogen evolution of [Ir-Py-Co]+ (blue) and [Ir(ppy)2(bpy)]+ with
[Co(dmgH)2PyCl] (red). Solid line: TON, dashed line: TOF. Reaction conditions:
0.1 mM PS, 0.1 mM catalyst, 1 M triethanolamine, 0.1 M HBF4. Solvent: aceto-
nitrile, under an atmosphere of argon. Irradiation centered at 525 nm (Fig-
ure 3).
Conclusion
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In summary, the new [Ir-Py-Co]+ dyad presents much greater
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Eur. J. Inorg. Chem. 2016, 1779–1783
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