Dissertation

|3.1 Brominated Phenanthrolines - A Gate to new Bridging Ligands|
with inequivalently halogenated tpphz derivatives that halogenation causes lower coordination
affinity at the brominated phenanthroline sphere due to the electron withdrawing effect of these
groups. This results in a selective ruthenium coordination into the unsubstituted N,N’ pocket of
tpphz.
[125, 126]
Furthermore, it is known from experiments by Rau et al. that 3,5,6,8-tetrabromophenanthroline
(phenBr 4 ) has a low coordination tendency toward ruthenium. [127] The attempts to prepare the
series [Ru(tbbpy) 3-n (phenBr 4 ) n
] 2+ (n = 1,2,3) succeeded only for n = 1 while the intermediates and
products toward the complexes with n = 2, 3 could not be prepared (even with longer reaction
times) or isolated, so that their characterization remains incomplete.
In the first attempt, simple model complexes were prepared which consist of a number of the
well known, solubility providing 4,4’-tert-butyl-2,2’-bipyridine (tbbpy) ligands at the ruthenium
center and a brominated ligand for metalorganic coupling reactions (see figure 44).
2+
N
N
N
Ru
N
Cl
Cl
+
N
N
Br
R
MW, 2h, reflux
(EtOH/H 2 O)
N
N
N
Ru
N
N
N
Br
R
R = H, Br
Figure 44: Synthesis of the ruthenium complexes with one phenBr-type ligand.
The synthesis of heteroleptic ruthenium polypyridine complexes of the type [Ru(̂LL) 2 (̂LL ′ )] 2+
is typically achieved from the cisoidal dichloro complex [Ru(̂LL) 2 Cl 2 ] and can be performed
according to the procedure of the work group of Rau et al. (method C1). Thereby a special
microwave reaction was used which allows for high yields and short reaction times. [120]
First, the starting materials [Ru(tbbpy) 2
Cl 2 ] and tbbpy were prepared according to the mentioned
procedures. Then, following the protocol of method C1, one equivalent of brominated
phenanthroline derivative was used in a microwave reaction together with [Ru(tbbpy) 2
Cl 2 ] to
prepare the desired complexes. The end of the reaction was indicated by a color change from
dark purple to bright red after refluxing the mixture for two hours in ethanol/water (4:1). Directly
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