Dissertation

|3.1 Brominated Phenanthrolines - A Gate to new Bridging Ligands|
Figure 40: Typical stacking pattern of the planar phenBr 2 molecules in the crystal lattice due to
π-π interaction, as observed in other crystal structures of substituted phenanthrolines.
Because of the high tolerance of the methyl substituents toward the harsh conditions 2,9-dimethyl-
1,10-phenanthroline was chosen as a substrate for the next test reaction. The bromination was
performed under the identical conditions (method L1), using a surplus (1.05 equivalents) of
bromine to achieve substitution of both, 5- and 6-position. Interestingly, a complete consumption
of bromine was observed according to the lightening of the formerly brown solution (see figure 41).
N
Br 2
N
(H 2 SO 4 SO 3 )
N
Br
Br 2
N
Br
Br 2
(H 2 SO 4 SO 3 )
N
(H 2 SO .
4 SO 3 )
N
Br
.
N
Br
.
N
Br
Figure 41: Successive bromination of 2,9-dimethyl-1,10-phenanthroline leading to triple
substitution.
Br
The formation of the 5,6-dibromo-2,9-dimthyl-1,10-phenanthroline could be confirmed by NMRand
DEI-MS-experiments. Characteristic was the isotopic pattern of the molecular ion (M + ,
m/z = 364) as well as the patterns of the expected fragments where one or two bromine atoms
were lost ([M-Br] + , m/z = 285 and [M-2Br] + , m/z = 206). In addition, a fraction of 10% of triply
brominated phenanthroline (3,5,6-position) was found in the product mixture, which equals the
surplus of used bromine ([M+Br] + , m/z = 444). Due to the high solubility of the methyl substituted
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