Metathesis of functionalized alkanes: understanding the unsolved problem
KAUST DepartmentPhysical Sciences and Engineering (PSE) Division
Permanent link to this recordhttp://hdl.handle.net/10754/659546
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AbstractThe aim of this dissertation is to discover the metathesis of functionalized alkane. The first chapter describes an overview of the catalysis field, the role of surface organometallic chemistry (SOMC) and the history of metathesis. The second chapter studies the decomposition of the alkane metathesis catalyst precursor based on WMe6 grafted on partially dehydroxylated at 700 °C silica (SiO2-700) [≡Si-O-WMe5] and its activity in the metathesis of non-coordinating substrates. We used thermal programmed desorption (TPD), in situ infrared-mass spectrometry (IRMS) and chemical techniques with nuclear magnetic resonance. We found evidence of decomposition of the catalyst by coordinating substrates (ester and alcohol) and its inactivity in the metathesis of siloxanes and silanes. [≡Si-O-WMe5] catalyzes the disproportionation of n-butyl-ferrocene to ferrocene and dibutylferrocene. The third chapter is dedicated to the strategy of protection of the catalyst active site by modification of the catalyst support. We modified conventional silica which was partially dehydroxylated at 500 °C, and KCC-1 supports by octyltriethoxysilane as well as 1,1,2,2- tetrahydro-perfluorooctyl-triethoxysilane and grafted the alkane metathesis catalyst precursor – W(CH3)6. The obtained materials have been thoroughly characterized and studied in catalysis showing the activity towards metathesis of olefins and alkanes, but were inactive in the metathesis of functionalized alkanes. The fourth chapter provides the strategy with which to design and metathesize a compatible functionalized alkane on well-defined alkane metathesis catalyst. We investigated the weak coordinating pyrrole-based family of substrates. While utilizing [≡Si-O-WMe5] with 1-(alkyl)-2,5- dimethyl-1H-pyrroles, traces of metathesis and isomerization products were observed. With these results, we synthesized a rigid aromatic molecule – 9-hexyl-9H-carbazole and reached 5 % conversion to lower and higher homologs. That result proved to be the first-ever known example of metathesis of a functionalized alkane. The fifth chapter details the strategy of utilizing the bimetallic catalysts based on supported late (Ir and Ru) and early (W and Ti) transition metal complexes, as well as a combination of late and early (Ru and Ti). All the systems were thoroughly characterized by FTIR and SS-NMR techniques and showed remarkable activity in the metathesis of alkanes. The sixth chapter provides conclusions and future outlook.