1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

Discussion and Results 3
3.2.4 Chemical Reactivity of Mono-Exocyclic Cycloketo-Porphyrin 53
As it has been dealt with a novel class of substances, also their chemical properties needed
to be investigated. Majorly those investigations focused on two subjects, the abilities of the
system to act as ligand and the opportunities the exocyclic ketone entails.
3.2.4.1 Metal Complexes
Based on the knowledge that the ability to form metal complexes is a common general
feature of porphyrins, it was tried to synthesize different metal derivatives of 53 by
application of standard procedures. The results have throughout been excellent leading to
the conclusion that the annulated structure is beneficial for the metallation process. Trials
provided metal complexes of Cu(II), Ni(II), Fe(III), Mn(III/V), Sn(IV), Co(II/III), In(III) and Zn(II)
serving as proof of principle that many metals independent on their size or oxidation state
can be implemented. Aiming at the development of novel photosensitizing materials, only
the zinc(II) and indium(III) complexes were subjected to further investigations, as those
metal centers are known to enhance the corresponding characteristics. Additionally, the
nickel(II) and copper(II) complexes, being of interest from the synthetic point of view, were
included into those investigations.
While the latter, Cu(II)-53 and Ni(II)-53, were directly obtained from the cyclization
procedure as mentioned before, Zn(II)-53 was synthesized utilizing the acetate method from
free base 53. Thereby the reaction of the free base in CH2Cl2 with zinc(II)acetate,
Zn(OAc)2·2H2O, dissolved in methanol, led to quantitative conversion within one hour. 93,96 To
obtain In(III)-53, free base 53 was reacted in benzonitrile with indium(III)chloride, InCl3, and
sodium acetate as base. 70b,113 The reaction furnished the desired target in 83 % yield with an
additional chloro ligand as counterion at the trivalent indium center as MALDI-TOF-MS
proved (m/z = 1041 [Chloro-In(III)-53] + (100 %), m/z = 1006 [In(III)-53] + (83 %)).
Those complexes have been characterized by NMR as accurately as possible whereas the
obtained data for Cu(II)-53 is not very conclusive. Due to paramagnetism a significant
broadening of signals is being observed in the quite narrow area between 9 and 1 ppm
containing the resonances for the arylic and the aliphatic protons like it is summed up in the
experimental section. For the β-pyrrolic protons, no signals are observable at all. This is not
surprising as it is known that even for highly symmetric Cu(II)-porphyrins these resonances
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