Syntheses of Novel Side-Arm Functionalized N-Heterocyclic Silylene Transition Metal Complexes
by Alexander Noel Paesch
Date of Examination:2019-06-13
Date of issue:2019-08-30
Advisor:Prof. Dr. Dietmar Stalke
Referee:Prof. Dr. Dietmar Stalke
Referee:Prof. Dr. Franc Meyer
Persistent Address:
http://dx.doi.org/10.53846/goediss-7616
Files in this item
Name:Dissertation_Alexander_Noel_Paesch_no_CV_web.pdf
Size:18.1Mb
Format:PDF
The following license files are associated with this item:
Abstract
English
The main field of silylene chemistry is emerging towards the utilization as strong σ-donating ligands for transition metal complexes. The focus of this area of chemistry was set primarily on the recreation of previous successes of known ligand systems, comparing their reactivities. The work presented here contributes to the essential exploration of new ways of accessing N-heterocyclic silylenes providing new features. In the first of three main parts this thesis concentrates on the investigation and introduction of phosphorous-based side-arms adapting the conventional method of substituting chloro benzamidinato silylene 1. The possibility of modifying 1 in this way holds an enormous potential for ligand design and tuning, but has not yet been pushed to its limits. The focus was set on researching bidentate ligands with a combination of softer (P(III)) and harder (Si(II)) donor atoms, to engage possible hemilabile complexation or encounter later transition metal atoms. The second and main part also focuses on the introduction of side-arms, but under the aspect of developing novel synthetic routes to TM complexes. Considering the purpose of isolating, characterizing and utilizing NHSi transition metal complexes, the prior isolation of the free functionalized silylene ligand can mostly be dispensed. The basic idea is built on the concept of “occupying” the free silylene 1 with the desired transition metal and thus simultaneously protecting the highly sensitive lone-pair of following operation conditions. The chloro group would remain unaffected and accessible for subsequent functionalization reactions. Such reactivity has not been investigated yet, but would open wide awareness to new synthetic approaches. Furthermore, a second method should be developed within the framework of this thesis, in regard to recent publications that revealed a certain behavior of the chloro group of 1 towards zinc organyl precursors, which will be investigated in order to exploit this reactivity. The behavior behind this observation should be transferred to the selective application in easily accessable organo transition metal salts. The synthesis of more complex ligands bearing one or more highly sensitive coordination sites is often as elaborate as the additional synthesis of a suitable metal precursor to gain very specific complexes, by means of reaction steps, workups, purifications and yields. In the last part, the focus was set on examining if the side-arm functionalization shows an influence on its reactivity. Thereby, the NHSiCl TM complexes, as well as their functionalized congeners, should be investigated towards their catalytical behavior by subjecting them to renowned transformations, the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC).
Keywords: Synthesis; N-heterocyclic Silylene; NHSi; transition metal complex; side-arm; hemilabile; bidentate; CuAAC; catalysis; group 11; awesome
