Abstract
9
This work describes several projects aimed at a systematic
investigation of the reaction of b-substituted
porphyrins with lithiumorganic reagents. Starting-point of this work was the
observation from Senge and Kalisch, that 2,3,7,8,12,13,17,18-octaethylporphyrin
and its nickel(II)complex react easily with organolithium reagents.1
The excellent reactivity was confirmed in this investigation. According to the
projects described aims section (chapter 3), the following results were obtained:
- It was demonstrated that use of various organolithium reagents (mostly LinBu,
LiPh) presents simple access to prepare nona-, deca-, undeca-, and
dodecasubstituted porphyrins with almost any desired regiochemical pattern
and combination of meso alkyl and aryl residues. Several
dodecasubstituted nickel(II)complexes were synthesized from
2,3,7,8,12,13,17,18-octaethylporphyrin in five steps. This investigation
gives important hints for the planning of an rational strategy to produce
porphyrins with mixed substitution pattern for the future (chapter 4.4). The
determination of eleven X-ray structures of porphyrins with different
substituent pattern confirmed known tendencies in macrocycle deformation of
symmetric porphyrins. The presence of both alkyl and aryl residues in the a
given molecule induces a mixing of distortion modes. The alkyl group has a
larger contribution to the overall conformation than an aryl group and
induces ruf distortion. The X-ray structure of the porphyrin 71
showed a nonplanar porphyrin with enantiotopic faces. On the basis of the
LiR-chemistry it should be possible to synthesize enantiotopic porphyrins
with functionalized groups, which might open new avenues towards
enantioselective catalysts` or receptor molecules.
- Despite their low solubility tetrabenzoporphyrins showed reactivity with
alkyllithium reagents. It was possibe to synthesize soluble benzoporphyrins
in one step by insertion of two substituent into the meso-position of
the macrocycle. Lower yields were observed in comparison to the reaction of
porphorinoid systems with an 2,3,7,8,12,13,17,18-octaethyl sceleton8
with LiR .
- Use of LiR1 and R2I as reagents allowed the
successful introduction of two substituents in the meso position of
the nickel(II)complex of b-ethyl substituted
porphyrins. These experiments resulted in the formation of porphodimethenes,
which were stable against oxidants. A wide variety of porphodimethenes can
be synthesized by this new method. It was possible, to synthesize
functionalized deca, undeca- and dodecasubstituted dihydroporphyrins.
- The postulated reaction mechanism for the free base 18 and the
nickel(II)complex 54 was verified with mechanistic studies. A
combination of deuteration experiments, trapping of the intermediates with
alkyl iodides, electronic absorption spectroscopy and variation of the
pH-values showed different intermediates in the reaction of the free base
and the nickel(II)complex. After addition of LinBu to the free
base 18 a phlorin anion was found that is stable against water. Only
at lower pH-values a regioselective protonation to porphodimethenes was
observed. In the case of the nickel(II)complex 54 two different
intermediates were obtained after addition of LinBu, a
phlorin-like and a porphodimethene-like intermediate. Both intermediate were
stable against hydrolysis in basic media and were oxidized with DDQ to the
respective porphyrin.
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