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@PHDTHESIS{Schmitz:1000454,
author = {Schmitz, Alexander Jonas},
othercontributors = {Leitner, Walter and Klankermayer, Jürgen},
title = {{E}ntwicklung von {P}incer {M}etall-{NHC}-{K}omplexen für
die indirekte {CO}$_{2}$-{H}ydrierung zu {M}ethanol am
{B}eispiel von {H}arnstoffderivaten},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2025-00369},
pages = {1 Online-Ressource : Illustrationen},
year = {2024},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University 2025; Dissertation, RWTH Aachen University, 2024},
abstract = {The present thesis describes the development of homogeneous
metal-NHC catalysts with a pincer ligand framework for the
indirect hydrogenation of CO2-derivatives to methanol. For
the investigation of this reductive transformation, a
particular focus is put on the hydrogenation of urea
derivatives. The use of CO2 as a renewable C1-building block
is central to establishing a greener chemical industry. Of
particular importance is the hydrogenation of CO2 to
methanol, which is as a key chemical linking many future
chemical value chains. The various strategies and challenges
associated with the hydrogenation of CO2 are presented in
Chapter 1. In addition, an overview is given of the key
structural features and the current state of research on the
CO2 hydrogenation using ruthenium as the metal centre, which
has attracted much attention due to its outstanding
performance. In this context, Chapter 2 describes the
motivation for the development and investigation of
metal-NHC complexes for indirect CO2 hydrogenation via urea
derivatives. The design and the synthesis of a novel
Ru(II)-NHC complex based on a pincer ligand is described in
Chapter 3. In the following Chapter 4, the newly established
catalyst was successfully applied to the hydrogenation of
urea derivatives. After optimising the reaction conditions,
various aromatic and aliphatic urea derivatives are tested
in the catalytic hydrogenation. Subsequently, mechanistic
studies are carried out to elucidate the reactive
intermediates and the elementary steps in the catalytic
cycle. In particular, a Ru(II)-ureate complex is formed and
identified as the catalytic resting state. In addition, an
unusual ruthenium dimer is crystallographically
characterised, providing important insights into the
catalytic behaviour of the catalyst. These mechanistic
investigations allow the proposal of a catalytic cycle based
on a stepwise hydrogenation of urea via the MLC pathway. The
development of catalytic systems based on earth-abundant 3d
metals is of particular importance in creating a more
sustainable chemistry. Following the diagonal relationship
in the periodic table, the synthesis of a Mn(I) analogue of
the developed pincer NHC-Ru(II) complex is reported in
Chapter 5. Moreover, the synthetic route and structure
determination of two structurally related NHC-Mn(I)
complexes are presented. DFT calculations are performed to
verify the formation of diastereomers in the synthesis of
the CPhNP-Mn(I) complex. Finally, the catalytic performance
of the NHC-Mn(I) complexes is investigated in the
hydrogenation of diphenylurea, showing promising stability
and activity for the CNP-type catalyst system.},
cin = {154110 / 150000},
ddc = {540},
cid = {$I:(DE-82)154110_20140620$ / $I:(DE-82)150000_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2025-00369},
url = {https://publications.rwth-aachen.de/record/1000454},
}
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