Dissertation

|3.3 NN-NHC-Ligand bbip: Toward Second Generation Catalysts|
comparison to the intramolecular system Ru(bbip)Rh which produces 16 moles of hydrogen per
mole of catalyst in the same time.
To further investigate the true nature of the catalyst and to obtain insights into the effect of colloid
formation on the catalytic activity, dynamic light scattering (DLS) experiments were performed.
As depicted in figure 110, catalytic mixtures of Ru(bbip)Ag, Ru(bbip)Pd and Ru(bbip) +
[Pd(ACN) 2 Cl 2 ] which were similar (inert cuvette instead of GC-vials) to the previously used
hydrogen formation experiments were in situ examined during catalysis.
5000
4000
particle size / nm
3000
2000
1000
0
0.0 0.5 1.0 1.5 2.0
irradiation time / h
Figure 110: Particle sizes in the catalysis mixtures of Ru(bbip)Ag (–●–), Ru(bbip)Pd (–●–), and
Ru(bbip) + [Pd(ACN) 2 Cl 2 ] (–●–) during the first two hours of catalysis as determined by DLS.
The results prove the suitability of this method to detect and trace the formation of particles
in the catalysis samples. Very prominent is the fast formation of large colloidal silver particles
in the mixture of triethylamine, acetonitrile and water from Ru(bbip)Ag during irradiation.
It can be expected that processes, similar to the photographic process, with reduction of
silver(I) lead to particle formation. This observation corresponds to the electrochemical results of
Ru(bbip)Ag, where irreversible redox processes were detected. Interestingly, no decomposition
of the complex in the catalytic mixture was detected in the dark under otherwise unchanged
conditions. Furthermore, light stability experiments in pure acetonitrile-d 3 show no signs of
decomposition after irradiation of the NMR-sample for several hours (compare chapter 3.3.8
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