Over the past decades, since the discovery of a single–site silica-supported catalyst for the alkane metathesis reaction by our group, we have been extensively working on the development of supported catalytic systems for the improved alkane metathesis reaction. During these developments, we understand the reaction mechanism and reached a new perspective for the synthesis of various supported bimetallic systems via the surface organometallic chemistry (SOMC) approach. Recently, with this bi-metallic system, we got a very high TON (10000) in propane metathesis reaction. As these catalysts are very efficient for linear alkanes we thought to apply it for cyclo-alkanes specifically, for cyclo-octane metathesis expecting better activity. Besides, the value of the ring alkanes are higher than the linear alkanes. The current work demonstrates a combination of [(ΞSi−O−)W(Me)5] and [(ΞSi− O−)Ti(Np)3 pre-catalyst with several supports (SiO2-700, SBA-15 and MCM-41) for metathesis of cyclooctane. The catalysts have been synthesized and fully characterized by elemental analysis (EA), FT-IR and NMR spectroscopies. After fully characterization the bi-metallic catalyst was tested for metathesis of cyclooctane with highest ever TON 2500 as compared to that of mono-metallic catalyst where we got 430 TON. Which again corroborates our prediction that bimetallic catalysts are better catalysts than monometallic catalysts.

Over the past decades, since the discovery of a single–site silica-supported catalyst for the alkane metathesis reaction by our group, we have been extensively working on the development of supported catalytic systems for the improved alkane metathesis reaction. During these developments, we understand the reaction mechanism and reached a new perspective for the synthesis of various supported bimetallic systems via the surface organometallic chemistry (SOMC) approach. Recently, with this bi-metallic system, we got a very high TON (10000) in propane metathesis reaction. As these catalysts are very efficient for linear alkanes we thought to apply it for cyclo-alkanes specifically, for cyclo-octane metathesis expecting better activity. Besides, the value of the ring alkanes are higher than the linear alkanes. The current work demonstrates a combination of [(ΞSi−O−)W(Me)5] and [(ΞSi− O−)Ti(Np)3 pre-catalyst with several supports (SiO2-700, SBA-15 and MCM-41) for metathesis of cyclooctane. The catalysts have been synthesized and fully characterized by elemental analysis (EA), FT-IR and NMR spectroscopies. After fully characterization the bi-metallic catalyst was tested for metathesis of cyclooctane with highest ever TON 2500 as compared to that of mono-metallic catalyst where we got 430 TON. Which again corroborates our prediction that bimetallic catalysts are better catalysts than monometallic catalysts.

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 polymeric products. 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.