Dissertation

|3.4 Outlook, Exploratory Investigations and Perspectives|
Figure 117: Solid state molecular structure of Ru(Br 2 bbip). Counter ions, hydrogen atoms and
coordinated solvents were omitted for clarity. Ellipsoids were drawn at the 50% probability level.
Compare table 16 an page 171 for selected bond lengths and angles.
3.4.3 NHC-Ligand edip: Further Development of Improved Catalysts
For a further stabilization of the NHC bound metal center and thus to avoid colloid formation
during photoreduction, it is important to expand the coordination sphere around the active metal.
With respect to the constitution of natural systems, such as the oxygen evolving complex or
the iron hydrogenases it may be helpful to construct multimetallic active sites. Furthermore, it
was shown by Auth et al. that an increased number of photocenters, as observed in natural
photosynthesis, may have a positive effect on the catalytic activity of the catalyst. [116, 117, 95, 19] In
a wider scope, polydentate ligands may lead to a self-assembly of polynuclear coordination arrays
with interesting application potential in catalysis, as shown by Sakai et al., and other fields such as
molecular information storage or molecular magnetism as demonstrated by Lehn et al.
[92, 197, 198]
In this context, caliper-like NHC ligands were prepared by Liu et al. to stabilize binuclear silver
complexes. [55] The transmetallation to the resulting palladium complexes was performed in the
work group of Rau (compare figure 28 (d) on page 39). Importantly, the latter was proven to
be an active catalyst for proton reduction in intermolecular photoredox catalyses in mixtures of
acetonitrile/triethylamine/water. [71]
Inspired by this work, the concept of a new bridging ligand was designed (see figure 118) which
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