Dissertation

|3.3 NN-NHC-Ligand bbip: Toward Second Generation Catalysts|
50
40
TON(H 2 ) after 5 h
30
20
10
0
1.0x10-5 2.5x10-5 5.0x10-5 1.0x10-4
2.5 10
c / mol/l
x -4
Figure 108: Catalysis concentration dependency of the intramolecularly working system
Ru(bbip)Pd. Denoted error bars represent the 3σ region of the GC accuracy.
times. The concentration dependency of Ru(bbip)Rh was measured, but due to the low activity
and the resulting very small concentrations of hydrogen gas in the headspace, the detection limit
of the GC method was reached for lower catalyst concentrations (detection limit is 0.05% of H 2 in
the GC sample, compare error bars in figure 108). Hence, it was not possible to separate the signal
from the noise, so that no clear statement about a possible catalyst concentration dependency of
the hydrogen production could be made.
Surprisingly, even the silver complex Ru(bbip)Ag showed some catalytic activity with 4 turnovers
within five hours (compare figure 107). Again, no concentration dependency could be determined
because of technical limitations. Finally, the control experiments, using the mononuclear complex
Ru(bbip) show, as expected, no hydrogen production.
The observed constant turnover frequency, the missing induction phase and the concentration
independency support the proposed intramolecular mechanism of the hydrogen formation, using
Ru(bbip)Pd. To affirm this presumption, further investigations were performed.
Using Ru(bbip) as chromophore and [Pd(ACN) 2 Cl 2 ] as pre-catalyst in a P ∼ B / C-system,
intermolecular control experiments were performed in the next step (see figure 109). All other
parameters (light source, solvent mixture, catalyst concentration) were left unchanged.
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