Dissertation

|3.3 NN-NHC-Ligand bbip: Toward Second Generation Catalysts|
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TON / mol(H 2 )/mol(cat.)
30
25
20
15
10
5
0
0 1 2 3 4 5
irradiation time / h
TON / mol(H 2 )/mol(cat.)
Figure 107: Time dependency of the catalytic activity in a 2 M solution of triethylamine in
acetonitrile with 5% water. Determined turnover numbers (TONs) and fitted plots of the hydrogen
generation of Ru(bbip)Pd (–●–), Ru(bbip)Rh (–●–), Ru(bbip)Ag (–●–), and reference Ru(bbip)
(–●–) (c complex = 250 µM).
hours at a constant turnover frequency (TOF) of 6 turnovers per hour. Important is the linearity
of the hydrogen production during that time. Furthermore, in contrast to other intramolecular
photoredoxcatalysts like [(tbbpy) 2 Ru(µ-tpphz)PdCl 2 ] 2+ , no induction period was observed since
hydrogen could be detected already after a few minutes of irradiation. Between five and ten hours
a plateau is slowly reached. This effect is commonly explained by the gas exchange through the
septum of the GC-vials (not designed for such catalysis experiments) or by side reactions in the
catalytic mixture, e.g. reactions which consume the produced hydrogen or alter the chromophorebridge-catalyst
structure.
Importantly, the catalytic activity of the Ru(bbip)Pd catalyst is concentration independent as
supported by independent studies with different concentrations (c = 10 µM, 25 µM, 100 µM and
250 µM, see figure 108) while and the intermolecular system Ru(bbip) + [Pd(ACN) 2 Cl 2 ] losses its
activity when low concentrations are applied.
The photocatalyst Ru(bbip)Rh (c = 250 µM) reaches a lower TON of 16 after 5 hours, whereas the
plateau is reached and no further increase in the TON can be detected after longer irradiation
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