The general objective of this thesis is the analysis of selective reactions for group VI
grafted metal complexes via methods and principles of SOMC. For this objective, three
approaches have been chosen.
The first chapter is an introduction to the topic of selectivity in catalysis, emphasizing
heterogeneous catalysis and more specifically the different approaches to support
catalysts on surfaces. The concept of catalysis by design is introduced as a new way to
use the surface as a ligand.
Chapter 2 presents the results of a library of well-defined catalysts of group VI with
identical catalytic functionality, but different ligand environment. The results reveal, that
metal-carbynes are able to switch their catalytic reactivity based on the substrate that
they are contacted with. The difference in reaction mechanisms and the differing
reactivities towards the substrates are presented. It can be concluded that the classical
ROMP is selectively achieved with cyclic alkene substrates leading to polymers whereas
cyclic alkanes yield exclusively higher and lower homologues of the substrate without
Chapter 3 presents the study of olefin metathesis of cis-2-pentene with metal-carbynes
of group VI, where the selectivity of the catalyst library towards yield of cis-/trans products
is analyzed. It is presented, that the ligand environment of the catalysts is showing an
influence in the selectivity. Rates of cis/trans isomerization of the products are high and
are approaching thermodynamic equilibrium at high conversion. Product isomerization,
thermodynamic equilibrium and reactivity differences between liquid phase and gas
phase products are analyzed.
Chapter 4 presents the full characterization of tungsten-hydrides by selective
transformation into tungsten-hydroxides. These newly discovered well-defined tungstenhydroxides are fully characterized by ICP, TEM, DRIFT, double quantum and triple
quantum solid-state NMR. The presented results allow to predict that tungsten-hydrides
on KCC-1700 are present as two distinct species. Catalysis results with cyclooctane show,
that due to burial of the complexes in the KCC-1700 surface the tungsten-hydrides are less
active towards cyclic alkane metathesis reactions with bulky cyclooctane than the metalcarbyne complexes.
Chapter 5 is giving a conclusion of results and an outlook for catalytic applications of the
generated tungsten-hydroxides of chapter 4.
|Date of Award||Nov 2020|
|Original language||English (US)|
- Physical Science and Engineering
|Supervisor||Jean-Marie Basset (Supervisor)|
- heterogeneous catalysis
- alkane metathesis
- metallo carbynes
- tungsten hydrides