TY  - GEN
N2  - This thesis deals with the synthesis and analysis of bispidine-iron(II)-complexes which act as model systems for nonheme iron enzymes. These enzymes participate in a wide range of natural oxidation reactions.
The first part of the thesis describes the synthesis of bispidine ligands with para-substituted pyridine donors as well as their iron complexes. For this purpose the literature known ligands L and LO were used and altered at their pyridine donors. The influence of these substituents on the reactivity of the corresponding iron complexes was analyzed in CH-activation reactions, sulfoxidations and in the oxidation of water.
The second part gives detailed information about the redox behavior of bispidine-iron-complexes in water and acetonitrile. Moreover, in case of bispidine-iron-complexes with pentadentate ligand systems, the influence of the coligand in sixth position was carefully investigated. In water, it was shown that the complexes of the pentadentate ligands LO, LU and their substituted analogues exist in an equilibrium of aqua- and hydroxido compounds. It was further demonstrated, that in acetonitrile Cl- shifts the FeII/III redox potential due to coordination to more negative values, whereas in water the only species detected are the aqua- and hydroxido species without Cl- having any influence on the redox potential. In addition, it was revealed that the FeIII/IV Redox potential of FeIV=O compounds is not accessible by the method of cyclic voltammetry. 
In the third part, the newly synthesized as well as the already known complexes were reacted with iodosylbenzene to form reactive FeIV=O species, which then were exposed to organic substrates. In these reactions, rate constants for CH-activation reactions and sulfoxidation were determined. Since trends in FeIII/IV redox potentials are expected to be closely related to the corresponding trends in FeII/III redox potentials, FeII/III potentials were correlated with rate constants. These correlations do not reveal a clear trend, which would allow a prediction of the reactivity of FeIV=O species in oxidation reactions, based on the FeII/III redox potentials.
The forth part of the thesis deals with the oxidation of CH-bonds with bispidine iron(II) complexes and dioxygen as the only oxidant. The reaction shows typical features of dioxygen activation but a thorough analysis indicates that this reactivity is not based on oxygen activation. Experiments with radical starters and radical scavengers, followed by a detailed spectroscopic analysis substantiate the assumption that the observed autocatalytic reaction is started by an autoxidation of the substrate. These findings lead to a proposed mechanism for the oxidation of organic substrates with the participation of iron(II) and dioxygen, which is based on autoxidative radical chemistry.
The fifth and last part of this thesis treats with the oxidative cleavage of water into dioxygen and protons. For this part the iron complexes with tetradentate bispidine ligands were used exclusively. Only iron complexes with tetradentate bispidine ligand systems show reactivity in the dioxygen generation when exposed to the oxidants cerium ammonium nitrate and sodium periodate. The redox potentials found in part two of this thesis were taken into consideration to conclude an influence of the potential on water oxidation. Here, it was found, that a high FeII/III potential is not beneficial for high yields of dioxygen.

A1  - Waleska, Arkadius
TI  - Untersuchungen zur Wasseroxidationskatalyse und zu Sauerstoffaktivierungs- und Oxidationsprozessen mit Bispidin-Eisenkomplexen
ID  - heidok15461
AV  - public
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/15461/
KW  - Sauerstoffaktivierung
KW  -  nichthäm
KW  -  Eisen-oxo
KW  -  Wasseroxidation
Y1  - 2013///
ER  -